Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session H1: Poster Session II (14:00 - 17:00)
Room: Exhibit Hall F
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H1.00001: GENERAL |
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H1.00002: Fairy-Tale Physics Farewell to Reality Bankrupting Physics: Baggott-Unzicker-Jones Critiques Shame Physics' Shameless Media-Hype P.R. Spin-Doctoring Touting Sci-Fi Veracity-Abandonment ``Show-Biz'' Spectacle: Caveat Emptor!!! Edward Siegel Baggott[Farewell to Reality: How Fairy-Tale Physics Betrayed Search For Scientific Truth]-Unzicker [Bankrupting Physics: How Top Scientists Are Gambling Away Credibility] shame physics shameless rock-star media-hype P.R. spin-doctoring veracity-abandoning touting sci-fi show-biz aided by online proliferation of uncritical pop-sci science-writers verbal diarrhea, all spectacle vs little truth, lacking Kant-Popper skepticism/ falsification, lemming-like stampedes to truth abandonment, qualified by vague adverbs: might, could, should, may,\textellipsis vs factual is! Physics, motivated by financial greed, swept up in its very own hype, touts whatever next big thing/cutting-edge bombast ad infinitum/ad nauseum, turning it into mere trendy carney sideshow, full of fury(FOF) but signifying absolutely nothing! Witness: GIGO claims string-theory holographic-universe causes cuprates optical conductivity; failed Anderson RVB cuprates theory vs. Keimer discovery all cuprates ``paramagnons'' bosons aka Overhauser SDWs; Overbye NYT holographic-universe jargonial-obfuscation comments including one from APS journals editor-in-chief re. its unintelligibility, FOF but signifying absolutely nothing INTELLIGIBLE!; Bak/BNL SOC tad late rediscovery of F$=$ma mere renaming of Siegel acoustic-emission!; 2007 physics Nobel-prize Fert-Gruenberg rediscovery of Siegel[JMMM 7,312(78); https://www.flickr.com/search/?q$=$ GIANT-MAGNETORESISTANCE] GMR. Each trendy latest big thing modulo lack of prior attribution aka out and out bombastic chicanery! Siegel caveat emptor ``Buzzwordism, Bandwagonism, Sloganeering for Fun Profit Survival Ego'' sociological-dysfunctionality thrives! [Preview Abstract] |
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H1.00003: Density Functional and Effective Hamiltonian Calculations of the Spin-Orbit Coupling in WS$_2$ Monolayers Mohammad Mahdi Valizadeh, Shanavas Veedu, Sashi Satpathy The monolayer metal dichalcogenides such as MoS$_2$ and WS$_2$ are currently an emerging class of 2D materials owing to their possible applications in 2D electronics including spintronics. The spin-orbit interaction coupled with broken structural inversion symmetry or external electric field, can give rise to interesting effects such as Rashba spin splitting. With the help of density functional theory based electronic structure calculations and tight binding Hamiltonian based models, we study the effect of an external electric field in monolayers of high-Z dichalcogenide WS$_2$. Density functional calculations predict strong spin-orbit coupling with a large Zeeman like splitting at the K-point in the H-structure, even in the absence of any external field. We also find Rashba splitting of bands at $\Gamma$ point close to the Fermi level which can be tuned using the applied electric field. Based on the DFT calculations, we derive an effective Hamiltonian for this system which offers a simple model to understand the interplay of spin-orbit and electric fields in this system. [Preview Abstract] |
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H1.00004: Measuring Speeds with Microwave Interferometry Logan Hillberry The speed of an approximately frictionless cart is simultaneously measured in two ways. A 10.5 GHz microwave source is used in the familiar Michelson interferometry setup with one of the arms being the mobile cart and the other being a stationary microwave receiver. As the cart travels, the changing interference pattern is captured on an oscilloscope which, when combined with the source frequency, can be used to determine the cart's speed. The second speed measurement is achieved by sending a laser beam across the cart's path into a photo detector which is connected a second channel on the oscilloscope. The cart breaks the beam and travels a distance equal to its length before allowing the beam to reach the photo detector again. Using the oscilloscope's timing measurement and the known cart length, one can readily calculate the cart's speed. Comparison of the two methods conveys agreement within error, confirming the path length difference model used to calculate the speed of the cart in the microwave interferometry method. [Preview Abstract] |
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H1.00005: Ageism Discrimination Crowdlynching Shames Physics Pretentions of Intellectual Honesty and Ethics: Extension Throughout Universities Shaming Education By Bankrupting Overdebted Student Defrauding: Caveat Emptor!!! J. Isalie, Druid Codben, Gruald Seidwinder, Ereich Heiller, Muddlekent Young, Hugene Stuntley, L.E.E Siegel, Charlatan deLiesie Ageism discrimination sociological-dysfunctionality crowdlynching shames physics pretentions of intellectual honesty and ethics! Extension to other departments:philo.,psych.,geo.,maths shames claims of honest education:BU,HU,NEU,UW,SDSU,ICTP/SISSA. Defrauding overdebted students, would be ``sciences'' become alas mere s\'{e}ances! Witness:70 year old Edward Siegel,PhD(70) firsts:multiband Hubbard-model decades pre-``Emery''; with Rosen/Feynman[IBM Conf.Comp./Math.(86)] trendy/ hyped ``Q-computing'' in ANN AI, google search-engine Page-Brin adaption; pre-trendy nanophysics [PSS(a) 11, 45(72);Scripta Met.13,913(79)];decade-earlier GMR discoverer[JMMM 7,312(78)] pre ``Fert''-``Gruenberg''; decade-earlier acoustic-emission F$=$ma rediscovery in Bak/BNL-hyped SOC; FUZZYICS Aristotle SoO rediscovery eliminating jargonial-obfuscation plaguing physics via implementation of Cohen-Stewart[Collapse of Chaos:Discovering Simplicity in ``Complex'' World] called for compl-icity/ simple-xity both simultaneously automatically;big-`data'disambiguation via HoT;AMS Joint Mtg.(02) proofs:FLT;P$\ne $NP;BSD conj.,Riemann-hypothesis as BEC; Benford's-law inversion discovering digits $=$ bosons; (87) Majorana-fermion {\&} HDM discoverer in complex-quantum-statistics in fractal-dimensions; ``it's a jack-in-the-box'' universe cosmology. [Preview Abstract] |
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H1.00006: PHYSICS EDUCATION |
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H1.00007: Half Lives for ``Irradiated'' Nonscience Majors Kathleen Geise, Peter Hallam, Rebecca Rattray, Robert Stencel, Tristan Wolfe We launched new hands-on radiation labs to supplement lecture material for undergraduate, non-science majors at the University of Denver to reinforce learning objectives during winter quarter 2014 and in order to help educate the public about nuclear energy decisions. Our learning objectives included: 1. differentiate between particle radiation and electro-magnetic radiation, 2. understand that particle radiation comes in alpha, beta and gamma types, 3. atomic and nuclear structure, 4. decay and half-life, 5. understand safe vs. unsafe doses and issues surrounding nuclear waste disposal. We used prelab surveys, prelab assessments, laboratory write-ups and quizzes to measure success with the learning objectives. [Preview Abstract] |
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H1.00008: Physics education of Japanese national colleges of technology in local community of Hokkaido Akihiro Kushino, Hidenori Matsui The national colleges of technology in Japan, called KOSEN, were established about 50 years ago aiming to educate 15 to 20 years old students to become engineers who were necessary in period of high economic growth of Japan. In present, environment surrounding us has changed. Examples are low birth rate in Japan and the great earthquake in Tohoku area. There are 4 KOSENs in Hokkaido and we jointly make many efforts to contribute to local community in science. We present our efforts in physics education. [Preview Abstract] |
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H1.00009: Multi-Rocket Thought Experiment Florentin Smarandache We consider $n $\underline {\textit{\textgreater }}\textit{ 2} identical rockets: $R_{1}, R_{2}$\textit{, \textellipsis , R}$_{n}$. Each of them moving at constant different velocities respectively $v_{1}, v_{2}$\textit{, \textellipsis , v}$_{n}$ on parallel directions in the same sense. In each rocket there is a light clock, the observer on earth also has a light clock. All $n +$\textit{ 1} light clocks are identical and synchronized. The proper time $\Delta t'$ in each rocket is the same. \begin{enumerate} \item If we consider the observer on earth and the first rocket $R_{1}$, then the non-proper time \quad $\Delta t$ of the observer on earth is dilated with the factor $D(v_{1}):$ \end{enumerate} or \quad $\Delta t = \quad \Delta t'D(v_{1}) $ \begin{enumerate} \item But if we consider the observer on earth and the second rocket $R_{2},$ then the non-proper time \quad $\Delta t$ of the observer on earth is dilated with a different factor $D(v_{2}):$ \end{enumerate} or $\Delta t = \quad \Delta t'D(v_{2}) $ And so on. Therefore simultaneously \quad $\Delta t$ is dilated with different factors $D(v_{1}), D(v_{2}$\textit{), \textellipsis , D(v}$_{n}),$ which is a multiple contradiction. [Preview Abstract] |
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H1.00010: ABSTRACT WITHDRAWN |
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H1.00011: ABSTRACT WITHDRAWN |
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H1.00012: Improving Students' Understanding of Lock-In Amplifiers Seth DeVore, Alexandre Gauthier, Jeremy Levy, Singh Chandralekha A lock-in amplifier is a versatile instrument frequently used in physics research. However, many students struggle with the basic operating principles of a lock-in amplifier which can lead to a variety of difficulties. To improve students' understanding, we have been developing and evaluating a research-based tutorial which makes use of a computer simulation of a lock-in amplifier. The tutorial is based on a field-tested approach in which students realize their difficulties after predicting the outcome of simulated experiments involving a lock-in amplifier and check their predictions using the simulated lock-in amplifier. Then, the tutorial guides and helps students develop a coherent understanding of the basics of a lock-in amplifier. The tutorial development involved interviews with physics faculty members and graduate students and iteration of many versions of the tutorial with professors and graduate students. The student difficulties and the development and assessment of the research-based tutorial are discussed. [Preview Abstract] |
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H1.00013: How to Combine Engines to Achieve High Speed, Hypersonic Speed, Speed of Light and Even Higher -Applications Celestin Mwizerwa, Celestine Nishimwe When Einstein left us, he left us a really big problem to solve, does anything can travel faster than the speed of light? There hasn't been any way to try this in the past, because there were any technology which could accelerate objects at this speed. What researchers tried to do, was to accelerate particles. But there must be a way to play with speeds so that, as we do math, we may practically multiply the speed by any number we want, we also may practically divide the speed by any number we want. In this paper I will try to show how. Also, In our real life, there might be a need of such high speeds, so that a lot of problems may be solved, as for example the airplane technology, electric power, space travel, car transmission, industrial high temperature and so on \textellipsis I do not say for sure that, the object will move faster than the speed of light, but, people who have ability may try to accelerate it at this speed and even faster to see what will happen as now it is very easy to realize. There are two ways; you go to space to do it or, you create a vacuum and move it inside. [Preview Abstract] |
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H1.00014: Development of Tunneling Spectroscopy Apparatus for Kelvin and Sub-Kelvin Measurements of Superconducting Energy Gaps by Multi-disciplinary students at a Liberal Arts University Matt Eckhardt Tunneling spectroscopy is an important technique used to measure the superconducting energy gap, a feature that is at the heart of the nature of superconductivity in various materials. In this presentation, we report the progress and results in developing high-resolution tunneling spectroscopy experimental platforms in a helium three cryostat, a 3 Kelvin cryocooler and a helium dip-tester. The experimental team working in a liberal arts university is a multi-disciplinary group consisting of one physics major, chemisty majors and a biology major. Students including non-physics majors learned and implemented current-voltage measurement techniques, vacuum system engineering, built electronic boxes and amplifier circuits from scratch, built custom multi-conductor cables for thermometry and current-voltage measurements, and performed conductance measurements. We report preliminary results. [Preview Abstract] |
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H1.00015: UNDERGRADUATE POSTERS |
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H1.00016: Two-Rockets Thought Experiment Florentin Smarandache Let $n $\underline {\textit{\textgreater }}\textit{ 2} be identical rockets: $R_{1}, R_{2}$\textit{, \textellipsis , R}$_{n}$. Each of them moving at constant different velocities respectively v$_{\mathrm{1}}$, v$_{\mathrm{2}}$, \textellipsis , v$_{\mathrm{n\thinspace }}$on parallel directions in the same sense. In each rocket there is a light clock, the observer on earth also has a light clock. All $n +$\textit{ 1} light clocks are identical and synchronized. The proper time \quad $\Delta t'$ in each rocket is the same. Let's focus on two arbitrary rockets $R_{i\thinspace }$and $R_{j} $from the previous $n$ rockets. Let's suppose, without loss of generality, that their speeds verify $v_{i}$\textit{ \textless v}$_{j}$. (1) In the reference frame of the astronaut in$ R_{i}$ it is like rocket$ R_{i}$is stationary and $R_{j} $moves with the speed $v_{j}-v_{i}$ . Therefore the non-proper time interval as measured by the astronaut in$ R_{i}$ with respect to the event in$ R_{j}$ is dilated with the factor$ D(v_{j}-v_{i})$ , i.e. $\Delta t_{i.j} = \Delta t'D(v_{j}-v_{i}),$and rocket $R_{j} $ is contracted with the factor $C(v_{j}-v_{i})$ $,$ i.e. $L_{j} = L_{j}^{'\thinspace }C(v_{j}-v_{i})$ $. $(2) \quad But in the reference frame of the astronaut in $R_{j} $it is like rocket $R_{j} $is stationary and$ R_{i}$ moves with the speed $v_{j}-v_{i}$ in opposite direction. Therefore, similarly, the non-proper time interval as measured by the astronaut in$ R_{j}$ with respect to the event in$ R_{i}$ is dilated with the same factor$ D(v_{j}-v_{i})$ , i.e. $\Delta t_{j.i} = \Delta t'D(v_{j}-v_{i})$ $,$ and rocket$ R_{i\thinspace }$is contracted with the factor $C(v_{j}-v_{i})$ $,$ i.e. $L_{i} = L_{i}^{'\thinspace }C(v_{j}-v_{i})$ $. $But it is a contradiction to have time dilations in both rockets. (3) Varying \textit{i, j in \textbraceleft 1, 2, \textellipsis , n\textbraceright } in this Thought Experiment we get again other multiple contradictions about time dilations. Similarly about length contractions, because we get for a rocket $R_{j}$, \textit{n-2} different length contraction factors: $C(v_{j}-v_{1})$ $, C(v_{j}-v_{2})$ \textit{, \textellipsis , C(v}$_{j}-v_{j-1})$ $, \quad C(v_{j}-v_{j+1})$ $,$ \textellipsis , $C(v_{j}-v_{n}) $ simultaneously! Which is abnormal. [Preview Abstract] |
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H1.00017: Study of Au/Cr multilayer thin-film surface morphology, structure and constituents on borosilicate glass, and quartz surfaces John Lavoie, Eric Kemble, Indrajith Senevirathne Au/Cr/substrate multilayer thin films have a wide area of applications in both industry and proof of concept investigations in device engineering. Borosilicate glass and quartz are used for substrate materials. Typically, Cr deposition on substrates give rise to Stanski-Krastonov (SK) like growth while Frank-van der Merwe (FM) like growth is desired in many engineering applications. A thermal evaporator is used to deposit Cr with a thickness of $\sim$ 100nm on the previously mentioned substrates. The additional Au layer is then deposited via magnetron sputter deposition at 100mtorr at low deposition rates ($\sim$ 1ML/min) onto the Cr thin film. These systems were then annealed using different temperatures for various durations. After annealing these systems were characterized via Atomic Force Microscopy (AFM) probes for surface topography and structure. Further, the ambient contamination and elemental distribution/diffusion at annealing was investigated via Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). [Preview Abstract] |
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H1.00018: Mu2e Extinction Monitor Testing at Fermilab Steven Boi, Ashlyn Shellito Extended versions of the Standard Model predict a small rate of neutrinoless muon-to-electron conversions. If verified, charged lepton flavor violation (CLFV) would point to new physics beyond the Standard Model. With a sensitivity of four orders of magnitude better than previous experiments, the Mu2e experiment at Fermilab will search for a specific muon-to-electron CLFV process in the presence of a nucleus. The Mu2e detector is comprised of many components including a particle tracker, calorimeter, stopping target monitor, cosmic ray veto, and proton beam extinction monitors. Researchers at Northern Illinois University constructed extinction monitoring prototypes used to detect and record residual out-of-time protons which could otherwise cause false muon-to-electron conversion signals. Initial tests of these prototypes were performed both at NIU using radioactive sources and at Fermilab's Test Beam Facility using a 120 GeV proton beam. Results from the extinction monitor prototype testing will be presented. [Preview Abstract] |
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H1.00019: Considering Hydrophobicity via Contact Angle Stability of Organic Thiols Measured with a Homemade Goniometer Mark Seraly, Brooke Ollander, Ariel Statman, Adele Poynor When water meets an extended hydrophobic surface, an ultra-thin, low-density depletion layer is expected at the interface. Exactly how the depletion layer changes with change in hydrophobicity is still an open question. An accurate measure of contact angle is essential in determining how water meets a hydrophobic surface. Utilizing a homemade goniometer with ImageJ software we investigate the stability of self-assembled organic thiol monolayers, 1-octadecanethiol (ODT) and 11-mercaptoundecanoic acid (MUA). We report the changes in contact angle due to exposure to air, water, and ethanol. Other factors that affect contact angles were also considered in our investigation. [Preview Abstract] |
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H1.00020: Comparative photoluminescence study of crystalline and nanostructured scintillators George McKinney, Warren McDonald, Marian Tzolov Scintillators are widely used for conversion of high energy radiation/particles to visible light which can be either directly observed or further converted to electrical signal in photomultipliers or solid state detectors. We compare the light emission properties of traditional crystalline scintillators with nanostructured films created in our laboratory with the potential for use as scintillators. We have studied zinc oxide (ZnO) nanowires, zinc tungstate (ZnWO$_{4}$) thin films, commercially available crystals of ZnO, ZnWO$_{4}$ and commercial scintillators of yttrium aluminum garnet (YAG) and yttrium aluminum perovskite (YAP). We will present the photoluminescence emission spectra, the intensity dependence of the emission, and the photoluminescence excitation spectra. We have found that the emission spectrum of zinc oxide nanowires becomes very intense at high excitation intensities and becomes comparable with the emission from the commercial scintillators. The excitation spectra indicate the presence of subgap electronic states in the nanostructured samples and in the commercial scintillators. This study contributes to our effort of creating electron detectors for scanning electron microscopy using nanostructured scintillators. [Preview Abstract] |
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H1.00021: Study of Temperature Sensitive Polymeric Microgels with Light Scattering and Spectrophometry Janna Mino, Justin Flaherty, Kiril Streletzky Hydroxypropylcellulose (HPC) polymer can be cross-linked to form microgel nanoparticles that undergo a temperature dependent volume phase transition. We studied the structure and dynamics of HPC microgels and HPC polymer that microgels were made from using Dynamic (DLS) and Static Light Scattering (SLS) and Spectrophotometry. Our results determined the transition behavior of the microgels and polymer as temperatures were varied from T$_{\mathrm{room}}$ to above the transition temperature T$_{\mathrm{C}}=$41C. The HPC microgels showed a reversible deswelling by a factor of 4-8 volume as temperature was brought above T$_{\mathrm{C}}$. The deswelling is caused by HPC chains becoming more hydrophobic at the T$_{\mathrm{C}}$ and aggregating together to diminish water contact. SLS measurements yielded the relative molecular weight M$_{\mathrm{W}}$ of microgels and M$_{\mathrm{W}}$ of polymer. We also found the change of microgels' M$_{\mathrm{W}}$ and R$_{\mathrm{g}}$/R$_{\mathrm{h}}$ with increase of solution temperature (T): M$_{\mathrm{W}}$ decreased steadily from 20C to 40C (possibly due to microgels losing water) and then increased with T rising to 50C (possibly due to loose polymer chains fusing into microgels). The R$_{\mathrm{g}}$/R$_{\mathrm{h}}$ ratio ranged from 0.4 to 0.7, consistent with a soft sphere and hard sphere models. The transition in polymer was found to be sharper than in microgels and the M$_{\mathrm{W}}$ of the polymer clusters above the transition was found to be 30 times larger then M$_{\mathrm{W}}$ of microgels. The light scattering study of microgels was complemented by Atomic Force Microscopy. [Preview Abstract] |
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H1.00022: Cathodoluminescence studies of commercial and nano-structured scintillators Warren McDoanld, George McKinney, Marian Tzolov Scintillators have applications in fundamental research and in consumer products, e.g. detectors, scanners, and televisions. This research focused on analyzing the cathodoluminescence of different single-crystal scintillators with an originally developed method for evaluation of their performance, which allows for a direct comparison of different scintillators. We have studied yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP) scintillators, zinc oxide single crystal, zinc tungstate single crystal, zinc oxide nanowires, and zinc tungstate film. The commercial scintillators are covered with conductive film which prevents low energy electrons from effectively interacting with the scintillator. We have varied the voltage accelerating the electrons with the intention of finding the threshold below which this effect will impact the performance of the scintillators. The same procedure was followed for the nanowires and zinc tungstate film which have enough conductivity and don't require a top conducting film. The threshold was established to be around 3 kV for the YAG and there is no threshold for the films, which perform much better at these low voltages. This property of the films has the potential for application in desktop scanning electron microscopes, where the accelerating voltage is low. The voltage dependence of the cathodoluminescence intensity follows an exponential trend and we present a model explaining it. [Preview Abstract] |
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H1.00023: Non-linear Multidimensional Optimization for use in Wire Scanner Fitting Alyssa Henderson, Balsa Terzic, Alicia Hofler To ensure experiment efficiency and quality from the Continuous Electron Beam Accelerator at Jefferson Lab, beam energy, size, and position must be measured. Wire scanners are devices inserted into the beamline to produce measurements which are used to obtain beam properties. Extracting physical information from the wire scanner measurements begins by fitting Gaussian curves to the data. This study focuses on optimizing and automating this curve-fitting procedure. We use a hybrid approach combining the efficiency of Newton Conjugate Gradient (NCG) method with the global convergence of three nature-inspired (NI) optimization approaches: genetic algorithm, differential evolution, and particle-swarm. In this Python-implemented approach, augmenting the locally-convergent NCG with one of the globally-convergent methods ensures the quality, robustness, and automation of curve-fitting. After comparing the methods, we establish that given an initial data-derived guess, each finds a solution with the same chi-square- a measurement of the agreement of the fit to the data. NCG is the fastest method, so it is the first to attempt data-fitting. The curve-fitting procedure escalates to one of the globally-convergent NI methods only if NCG fails, thereby ensuring a successful fit. This method allows for the most optimal signal fit and can be easily applied to similar problems. [Preview Abstract] |
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H1.00024: Superatomic Molecular Orbitals of C60: First-Principles calculation Jason Bonacum, Guo-Ping Zhang, Kyle Drake The molecular structure of buckminsterfullerene or C60 allows for highly delocalized orbitals, but they are not like a planewave, which is completely delocated. Instead they form super atomic molecular orbitals (SAMO). These SAMO are like regular atomic orbitals, but the molecule now acts as a single atom. This implies that SAMO should follow trends similar to that of regular atomic orbitals. Using density functional theory in a real grid mesh, we computed these SAMO of C60. We found that the trend in the orbitals corresponding to these eigenstates can then be compared to the valence electron orbital trends on the periodic table. This information is useful for determining the properties of C60 that are a result the SAMO, and these properties are important in the applying C60 as building blocks in the field of nanoscience. [Preview Abstract] |
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H1.00025: An investigation of Au/Ti multilayer thin-films: surface morphology, structure and interfacial/surface migration of constituents under applied thermal stress Indrajith Senevirathne, Eric Kemble, John Lavoie Multilayer thin films are ubiquitous in industry. Au/Ti/substrate is unique due to possible biological applications in proof of concept devices. Material used for substrates include borosilicate glass, and quartz. Typical Ti depositions on substrates give rise to Stanski-Krastonov (SK) like growth while Frank-van der Merwe (FM) like growth is preferred. Ti films with thickness of $\sim$ 100nm were deposited onto varying substrates using a thermal evaporator. The additional Au layer is then deposited via magnetron sputter deposition at 100mtorr at low deposition rates ($\sim$ 1ML/min) onto the Ti thin film. These systems were annealed at varying temperatures and at different durations. Systems were investigated via AFM (Atomic Force Microscopy) probes to examine the surface morphology, and structure. Further, the ambient contamination and elemental distribution/diffusion at annealing was investigated via Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). [Preview Abstract] |
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H1.00026: Graphene Calisthenics: Modeling the Polymer-induced Graphene Stretching for Next Generation Electronics Mandy Huo, Kacey Meaker, Su-Ann Chong, Michael Crommie Graphene is one atomic layer of graphite. It is stronger than steel yet very elastic. Although graphene is a semiconductor with no band gap, we can introduce a gap using various methods in order to make it useful in next-generation electronics. One way to do this is to strain graphene. While we can easily strain graphene uniaxially, this type of strain does not produce appreciable band gaps until relatively high strain percentages close to the fracture point of graphene. However, with a special strain geometry we can produce band gaps well before reaching the breaking point of graphene. This has been done experimentally, but not in a controlled manner. From previous research, strain percentages around 10 percent produce appreciable band gaps. Increasing the strain will increase the size of these gaps, but graphene breaks at around 20 percent strain. We propose to control the amount by which we strain graphene by placing it on a special polymer which expands when light is shone on it. In this project we use COMSOL, a finite element analysis software, to estimate the strain resulting in graphene due to stretching it with a given polymer geometry to find the shapes which will produce the specified strain. [Preview Abstract] |
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H1.00027: Neutron flux characterization of californium-252 Neutron Research Facility at the University of Texas - Pan American by nuclear analytical technique Kareem Wahid, Patrick Sanchez, Mohammad Hannan In the field of nuclear science, neutron flux is an intrinsic property of nuclear reaction facilities that is the basis for experimental irradiation calculations and analysis. In the Rio Grande Valley (Texas), the UTPA Neutron Research Facility (NRF) is currently the only neutron facility available for experimental research purposes. The facility is comprised of a 20-microgram californium-252 neutron source surrounded by a shielding cascade containing different irradiation cavities. Thermal and fast neutron flux values for the UTPA NRF have yet to be fully investigated and may be of particular interest to biomedical studies in low neutron dose applications. Though a variety of techniques exist for the characterization of neutron flux, neutron activation analysis (NAA) of metal and nonmetal foils is a commonly utilized experimental method because of its detection sensitivity and availability. The aim of our current investigation is to employ foil activation in the determination of neutron flux values for the UTPA NSRF for further research purposes. Neutron spectrum unfolding of the acquired experimental data via specialized software and subsequent comparison for consistency with computational models lends confidence to the results. [Preview Abstract] |
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H1.00028: Determining the Effect of Aluminum Oxide Nanoparticles on the Aggregation of Amyloid-Beta in Transgenic \textit{Caenorhabditis elegans} Suhag Patel, John Matticks, Carina Howell The cause of Alzheimer's disease has been linked partially to genetic factors but the predicted environmental components have yet to be determined. In Alzheimer's, accumulation of amyloid-beta protein in the brain forms plaques resulting in neurodegeneration and loss of mental functions. It has been postulated that aluminum influences the aggregation of amyloid-beta. To test this hypothesis, transgenic \textit{Caenorhabditis elegans}, CL2120, was used as a model organism to observe neurodegeneration in nematodes exposed to aluminum oxide nanoparticles. Behavioral testing, fluorescent staining, and fluorescence microscopy were used to test the effects of aggregation of amyloid-beta in the nervous systems of effected nematodes exposed to aluminum oxide nanoparticles. Energy-dispersive x-ray spectroscopy was used to quantify the total concentration of aluminum oxide that the worms were exposed to during the experiment. Exposure of transgenic and wild type worms to a concentration of 4 mg mL$^{-1}$ aluminum oxide showed a decrease in the sinusoidal motion, as well as an infirmity of transgenic worms when compared to control worms. These results support the hypothesis that aluminum may play a role in neurodegeneration in \textit{C. elegans}, and may influence and increase the progression of Alzheimer's disease. [Preview Abstract] |
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H1.00029: Building Measurement Apparatus: A Case Study Matthew Mahaffey, Ron Sinton The experimental process of designing, constructing, and implementing a measurement apparatus is discussed. A Sinton Instruments FMT-350 solar module tester is the chosen example to illustrate the successful implementation of scientific apparatus to mimic phenomena of interest. We examine the process of attempting to simulate the AM 1.5 G solar spectrum with xenon flash bulbs and optical filters. Due to the operating conditions of the components chosen to mimic the characteristics of this phenomenon, it is crucial to understand the ways in which the apparatus deviates from the desired result. At lower intensities and delayed measurement windows over time the spectral emission demonstrates red shifting due to the ratio of black body radiation to the spectral emission bands from the xenon flash. By monitoring these shifts, we develop an understanding of a correction factor that can be applied to acquired data appropriately. Additionally, we discuss the allowable tolerances as outlined by independent certification boards and how they relate to these types of devices. [Preview Abstract] |
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H1.00030: Specific Heat of Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{4}$Sb$_{12}$ Near 300K Taylor McCullough-Hunter, Thomas Nichols, Hank Anderson, Pei-Chun Ho, M. Brian Maple, Tatsuya Yanagisawa The filled skutterudite compound, PrOs$_{4}$Sb$_{12}$, displays unconventional superconductivity at a relatively low critical temperature T$_{\mathrm{c}}=$1.85K. To gain better insight into this phenomenon, we study the effect of ferromagnetism on the unconventional superconductivity by using Neodymium- doped samples Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{4}$Sb$_{12}$. We measured the heat capacities of the sample with x$=$1, 0.75, 0.5, and 0.25 using relaxation calorimetry of finite heat pulse width in a cryocooler system from 11K to 300K. The electronic specific heat coefficient $\gamma $, from the analysis of specific heat, of end member compound x$=$1 concentration is found to be approximately 60 mJ/K$^{2}$-mol; this is smaller than previously estimated specific heat of approximately 520 mJ/K$^{2}$-mol, but it is still relatively large when compared to simple metals. Also at high temperature (above 11K), there are no deviations in the specific heat data between sample with x$=$1 and x$=$0.5 concentration. This poster will describe the technique used in obtaining the data and report the result analysis of specific heat measurements from sample with x$=$1, 0.75, 0.5, and 0.25 concentrations. [Preview Abstract] |
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H1.00031: Thermopower Puck for Measurement of Thermodynamic Properties Andres Vargas, Ryan Fukuda, Nicholas Soliz, Pei-Chun Ho A thermopower puck was created in order to measure the thermoelectric power and thermal conductance of strongly correlated electron materials from 10K to 300K. The puck consists of a 2k$\Omega $ resistivity heater and 2 thermometers. The heater is connected to the top of the sample and applies heat until thermal equilibrium is reached. This creates a temperature gradient across the sample and is read by the 2 thermometers, one reading the hotter temperature and the other reading the colder temperature. The wire that is used as the thermal anchor for the high temperature thermometer, which is electrically isolated from thermometer, is also used as one of the leads to measure the thermal voltage produced across the sample. To calibrate the measurement probe, the thermoelectric power and thermal conductance of a nickel sample, which was purchased from Quantum Design, was measured. The data obtained qualitatively agrees with the literature data provided to us by Quantum Design. For future work, we will be using the measurement probe to investigate the thermodynamic properties of intermetallic compounds. [Preview Abstract] |
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H1.00032: Pregrowth and Biofilm formation of Bacillus subtilis on Glass Studied via AFM, SEM and Optical Microsopy Sydney Stutzman, Michelle Otte, Joseph Calabrese, Reshani Senevirathne, Indrajith Senevirathne Lock Haven University of Pennsylvania - Research into surface adhesion properties and the selectivity of bacteria towards glass will provide a better understanding of biofilm formation and how this formation will in turn effect hospital and laboratory settings. Investigation was focused on quantifying the selectivity of non-pathogenic B. subtilis - on soda lime glass substrates. Standardized Corning$^{\textregistered}$ 2947-75X25 microscope glass slides were used as the surface for bacterial attachment and facilitation of preliminary growth and formation of biofilms. Observations will be discussed both quantitatively and qualitatively. Structure morphology was investigated via Atomic Force Microscopy, Scanning Electron Microscopy and complemented with Optical Microscopy. [Preview Abstract] |
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H1.00033: ABSTRACT WITHDRAWN |
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H1.00034: Estimation of the Thickness of the Interface in Polyoctenamer-Nanodiamond Composites by Thermogravimetric Analysis Arnold Fonseca, Alejandro Castillo, Angel Maldonado, Julian Velazquez, Edgar Rodriguez In polymer-based nanocomposites, the macromolecular chains surrounding the nanoparticles interact with them, defining a thin layer of material known as interface. The interface exhibits modified physical properties compared to the polymeric matrix; shifts of the glass, melting, and crystallization temperatures have been reported elsewhere [1, 2]. The polymeric matrix of these nanocomposites is polyoctenamer (PO). PO has a glass transition temperature of -65 oC, melting temperature of 55 oC, and an average degree of crystallinity of about 30 {\%}. Nanocomposites of PO-ND containing various concentrations of ND have been obtained by melt mixing at 30 oC, using a counter-rotating two-screw mixer (POLYLAB). Samples containing 0, 0.05, 0.10, 0.25, 0.50, 1.00, 2.50, 5.00, 7.50, and 10 {\%} wt. ND dispersed within PO have been obtained. The thermal stability of the as obtained nanocomposites has been investigated by thermogravimetric analysis, using a Q 50 from TA Instruments. The measurements have been performed in nitrogen atmosphere at various heating rates (5, 10, 20, 30, and 40 oC/min). Additional measurements by Raman, Differential Scanning Calorimetry, and Wide Angle X Ray are supporting thermal analysis data. [Preview Abstract] |
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H1.00035: Self-Healing of biocompatible polymeric nanocomposities Omar Espino, Dorina Chipara Polymers are vulnerable to damage in form of cracks deep within the structure, where detection is difficult and repair is near to impossible. These cracks lead to mechanical degradation of the polymer. A method has been created to solve this problem named polymeric self healing. Self healing capabilities implies the dispersion within the polymeric matrix of microcapsules filled with a monomer and of catalyst. Poly urea-formaldehyde microcapsules used in this method are filled with dicyclopentadiene that is liberated after being ruptured by the crack propagation in the material. Polymerization is assisted by a catalyst FGGC that ignites the self healing process. Nanocomposites, such as titanium oxide, will be used as an integration of these polymers that will be tested by rupturing mechanically slowly. In order to prove the self healing process, Raman~spectroscopy, FTIR, and SEM are used. [Preview Abstract] |
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H1.00036: Monte Carlo simulation study of self-assembly of nanoparticles on Cayley trees Conan Zhao, Eric Schwen, Andrew Seredinski, Vincent Kim, Brian Simpson, William Banks, Jonathan Cook, Dan Mazilu, Irina Mazilu We present analytical and computational results for a cooperative sequential model with evaporation on general Cayley trees. In particular, we focus on the time dependence of the particle density for a wide range of parameters, such as attachment and detachment rates, tree coordination number, initial and boundary conditions. The model proposed can be used for the modeling of drug encapsulation of nanoparticles using synthetic polymers known as dendrimers, and well as ionic self-assembly of nanoparticles to create optical coatings. Computational results for silica optical coatings using the Ionic Self-Assembled Monolayer (ISAM) technique were compared with experimental results. [Preview Abstract] |
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H1.00037: Nonaqueous Synthesis of Gadolinium and Neodymium Nanoparticles R. Fukuda, M. Castro, P.-C. Ho, S. Attar, M. Golden, D. Margosan Nanoparticles are of great interest due to their magnetic properties, such as superparamagnetism, that are not exhibited by their bulk counterparts. Gd and Nd are being tested by applying the reverse micelle method. The reverse micelle method consists of using a surfactant with a large nonpolar solvent to polar solvent ratio to form spherical cages that control the size of the products. Many studies involving the reverse micelle method employ water as the polar solvent. Since Gd and Nd are highly reactive to water, methanol is used as a replacement with hexane or heptane as the nonpolar solvent. Gadolinium chloride or neodymium nitrate are reduced using sodium borohydride after the reverse micelles encapsulate the rare earth compound. Scanning electron microscopy (SEM) and light microscopy show small, spherical clusters with diameters in the micron range. Higher magnification of the SEM melted the clusters, even after cooling the sample to 87 K. The sample was coated with Pt to prevent melting. Energy dispersive x-ray measurements were conducted to find the chemical composition of the clusters, but the sample signals were too small to make a conclusion. Future growths will use the surfactant DDAB instead of AOT since DDAB is more stable when examined with SEM. [Preview Abstract] |
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H1.00038: ABSTRACT WITHDRAWN |
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H1.00039: Electric field dependent dielectric response of alumina/silicone oil colloids Louis Magallon, Stephen Tsui We investigate the dielectric response of a mixture of alumina nanopowder and silicone oil. Frequency and electric field dependent measurements of another insulating colloid, i.e., urea-coated Ba$_{\mathrm{0.8}}$Rb$_{\mathrm{0.4}}$TiO(C$_{\mathrm{2}}$O$_{\mathrm{4}})_{\mathrm{2}}$ nanoparticles immersed in silicone oil, revealed universal dielectric response (UDR) characteristics and, with the application of high voltage, a negative capacitance. Alumina in silicone oil represents a simpler system in which to perform similar dielectric investigation. This colloid is sandwiched in a parallel plate capacitor cell, and the complex impedance is measured via lock-in amplifier at various frequencies and applied dc biases. Furthermore, we will compare and discuss the dielectric behaviors of different sized suspended alumina particles. [Preview Abstract] |
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H1.00040: Defect Detection in Superconducting Radiofrequency Cavity Surface Using C$++$ and OpenCV Samantha Oswald Thomas Jefferson National Accelerator Facility (TJNAF) uses superconducting radiofrequency (SRF) cavities to accelerate an electron beam. If theses cavities have a small particle or defect, it can degrade the performance of the cavity. The problem at hand is inspecting the cavity for defects, little bubbles of niobium on the surface of the cavity. Thousands of pictures have to be taken of a single cavity and then looked through to see how many defects were found. A C$++$ program with Open Source Computer Vision (OpenCV) was constructed to reduce the number of hours searching through the images and finds all the defects. Using this code, the SRF group is now able to use the code to identify defects in on-going tests of SRF cavities. Real time detection is the next step so that instead of taking pictures when looking at the cavity, the camera will detect all the defects. [Preview Abstract] |
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H1.00041: A Solid Polarized Target for CLAS12 at Jefferson Lab Mathieu Ehrhart To be able to study the spin-dependence of the nucleon structure with electron scattering experiments, targets providing spin-polarized nuclei are needed. We report on the development of a new solid polarized target for the CLAS12 detector, presently being installed in Jefferson Lab's Hall B. The technique of dynamic nuclear polarization (DNP) requires very low temperatures around 1 Kelvin and a high magnetic field of around 5 Tesla. The very large natural polarization of free electrons inside the target material under these conditions is transferred to the nuclei via microwave radiation (electron Larmor frequency). The polarization of the protons and deuterons is measured with the nuclear magnetic resonance (NMR) technique. [Preview Abstract] |
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H1.00042: Characterization of universal dielectric response and negative capacitance in compressed nanopowders Madison Perry, Stephen Tsui Universal dielectric response (UDR) has been reported in disordered systems exhibiting percolative electrical conduction. Measurements of the complex impedance of a compressed pellet made up of alumina nanopowder reveal a low frequency dispersion of the off-phase component consistent with UDR. However, upon the application of applied dc bias beyond a certain voltage threshold, the dielectric behavior deviates from UDR and exhibits negative capacitance, which manifests as a pseudo-inductive phase angle in the complex impedance. This phenomenon has also been previously reported in other compressed nanopowder systems. We hereby examine the electrical impedances of various pellets made of different sized alumina nanopowders in an effort to correlate their applied bias-dependent dielectric behaviors with particle size. [Preview Abstract] |
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H1.00043: Real-Time Observation of Cell and Carbon Nanotube Interactions Michelle Chen, Melanie Broman, Claire Mathews, Eric McPherson Carbon nanotubes have been widely researched for disease diagnosis and drug delivery applications. However, its impact on biological systems is yet to be sufficiently understood. We studied optical imaging of Chinese hamster ovarian (CHO) cells exposed to various carbon nanotubes concentrations at various time points. The cell stress due to carbon nanotubes exposure is accessed via morphological changes of the CHO cells. Data showed that cell death increases with increasing carbon nanotube concentration and time exposure. To continuously view such changes of any one individual cell, we constructed an optically transparent miniaturized incubator that fits on a microscope stage. This specific incubator is able to maintain desirable temperature, humidity, and CO2 concentration to allow proper cell growth. Such incubator can be used to track real-time interactions of any cells and nanomaterials for future data collection. [Preview Abstract] |
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H1.00044: Home-built Surface Plasmon Resonance Apparatus for Studying Interactions Between Water and a Hydrophobic Surface Dylan McNany, Erin Brown, Shannon Petersen, Adele Poynor Water acts in many anomalous ways, especially when near a hydrophobic surface. Surface plasmon resonance (SPR), a quantum optical method is used to study these unusual effects. Through the use of SPR, studies of the depletion layer (a very thin low-density layer, only a few nanometers thick) can be conducted. Employing a home-built SPR device, along with a monolayer coated gold slide, studies are conducted using a variety of differing dielectrics (water, air, methanol). Modifications of the SPR apparatus allow us to find the assumed thickness of the depleted region. [Preview Abstract] |
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H1.00045: Simulations of MHD Dynamo With and Without the Reversal Surface D. Martin, D. Craig, J.A. Reusch Fluctuations in the Reversed Field Pinch (RFP) are dominated by Fourier mode numbers m=0 and m=1. The velocity and magnetic fluctuations drive a dynamo which redistributes current in the plasma. In experiments, m=0 modes and dynamo due to m=1 modes are highly dependent on the existence of the reversal surface in the plasma. We investigate the effects of reversal surface on magnetic and velocity fluctuations using a magnetohydrodynamic simulation to model the plasma with and without a reversal surface. We find that while m=0 modes are suppressed through the removal of the reversal surface, magnetic m=1 amplitudes are not affected. Velocity fluctuations for both modes decrease with the reversal surface removed. Work funded by USDOE. [Preview Abstract] |
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H1.00046: Random sequential adsorption of monomers with evaporation: exact results and application to ionic self-assembly Andrew Seredinski, Eric Schwen, Brain Simpson, Vincent Kim, Carlos da Fonseca, H.T. Williams, Irina Mazilu, Dan Mazilu We present an exact solution for the time-dependent particle density for a general random sequential adsorption model with evaporation. We relate this model to the experimental technique of ionic self-assembly of nanoparticles. We discuss the usefulness and the limitations of our model by comparing it to both Monte Carlo simulations and experimental results. [Preview Abstract] |
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H1.00047: Two-dimensional cooperative sequential adsorption with evaporation for ionic self-assembly of nanoparticles Eric Schwen, Vincent Kim, Brian Simpson, Jonathan Cook, Irina Mazilu, Dan Mazilu We present an analytical model for the process of ionic self-assembly of nanoparticles. This process is used for the creation of antireflective coatings and the analytical model for the particle density can be applied to predict the index of refraction. We created a cooperative sequential adsorption with evaporation model on a two-dimensional lattice in which particles are both deposited and evaporated from the surface and adsorption rates depend on the occupation of neighboring sites. By assuming translational invariance, we were able to solve for a self-consistent equation for the steady state coverage of the surface. Monte Carlo simulations show an excellent match between the analytical model and mean field solution. We related our model to the experimental results for varied colloidal suspension concentrations to determine the relationship between the parameters of our model and particle concentration. [Preview Abstract] |
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H1.00048: Modification of a Scanning Tunneling Microscope for Measurement of Ballistic Electron Emission Microscopy Satcher Hsieh, Jeongmin Hong, Jeffrey Bokor Magnetic memory and logic devices show great promise for integration with, and even replacement of, conventional complementary metal-oxide-semiconductor (CMOS) architectures. In order to characterize materials and deposition techniques for these devices, ballistic electron emission microscopy (BEEM) is used. BEEM is a spatially resolved metrological tool most commonly used for subsurface interface structures at the nanometer scale. We modify a scanning tunneling microscope (STM) to perform BEEM measurement via design and fabrication of a novel sample stage. Furthermore, we design and fabricate an external magnetic field source that encapsulates the sample stage, setting the foundation for future measurement of ballistic electron magnetic microscopy (BEMM). Instrumentation of the device and characterization of a sample with an ohmic interface, Ni-Si, are implemented and discussed. [Preview Abstract] |
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H1.00049: Characterizing superconducting thin films using AC Magnetic Susceptibility C.H. Mahoney, J. Porzio, M.C. Sullivan We present our work on using ac magnetic susceptibility to determine the critical temperature of superconducting thin films. In ac magnetic susceptibility, the thin film is placed between two coils. One coil carries an ac signal, creating a varying external magnetic field. We measure the voltage induced in the pick-up coil on the opposite side of the sample and measure how the sample magnetization changes as the temperature changes. We will present our work to use ac susceptibility to determine critical temperature and superconducting volume fraction. Using our own analysis program, we are able to accurately locate the critical temperatures of the samples and determine the transition width. For the superconducting volume fraction, we etch samples in order to control the thicknesses of the sample and measure how much of the material grown on the surface is superconducting. [Preview Abstract] |
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H1.00050: Low-energy electron diffraction study of Si(111)-($\surd $3x$\surd $3)R30$^{\circ}$ -B K.E. Marino, Y.T. Huang, R.D. Diehl, Weison Tu, Daniel Mulugeta, P.C. Snijders, H.H. Weitering Metal-semiconductor interfaces are important for the function and manufacture of advanced electronics, such as those used in computers, tablets and phones.~ They also exhibit many interesting physical phenomena that are interesting from a fundamental point of view, including exotic phases and phase transitions.\footnote{Gonz\'{a}lez, Guo, Ortega, Flores, Weitering. Phys. Rev. Lett. \textbf{102}, 115501 (2009)} This study involves the analysis and modeling of the surface structure of a thin film of boron on the Si(111) surface.~ The addition of metal atoms to the surface of Si(111) simplifies its structure by removing a ``rippling'' that is present on the clean surface.~ The low-energy electron diffraction (LEED) data were measured at a surface temperature of 80 K at ORNL. The LEED analysis utilized the SATLEED analysis programs. The results are similar to those obtained in an earlier LEED study for this interface, but the precision is higher due to the larger dataset employed.\footnote{P. Baumgartel \textit{et al.} Phys Rev B. \textbf{59} (1999)}$^,$\footnote{H. Huang, S. Y. Tong, W. S. Yang, H. D. Shih, F. Jona. Phys Rev B. \textbf{41 }(1990)} The results of this study will be compared to other studies of this and similar systems. We acknowledge the Eberly College of Science for funding this project. [Preview Abstract] |
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H1.00051: Development of Numerical Methods to Simulate Electron Diffraction in Real Time Stephen Blama, Jia-An Yan Using Gaussian wave packet propagation, we present a numerical study of the ultrafast electron diffraction in real space and in real time. The time-dependent Schrodinger equation is solved using both Crank-Nicolson and Taylor expansion methods. Detailed results of the wave packet scattered by different one-dimensional and two-dimensional potential profiles will be presented. [Preview Abstract] |
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H1.00052: Temperature dependence of conductivity measurement for conducting polymer Leandro Gutierrez, Jesus Duran, Anne Isah, Patrick Albers, Michael McDougall, Weining Wang Conducting polymer-based solar cells are the newest generation solar cells. While research on this area has been progressing, the efficiency is still low because certain important parameters of the solar cell are still not well understood. It is of interest to study the temperature dependence of the solar cell parameters, such as conductivity of the polymer, open circuit voltage, and reverse saturation current to gain a better understanding on the solar cells. In this work, we report our temperature dependence of conductivity measurement using our in-house temperature-varying apparatus. In this project, we designed and built a temperature varying apparatus using a thermoelectric cooler module which gives enough temperature range as we need and costs much less than a cryostat. The set-up of the apparatus will be discussed. Temperature dependence of conductivity measurements for PEDOT:PSS films with different room-temperature conductivity will be compared and discussed. [Preview Abstract] |
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H1.00053: Imaging and Laser Spectroscopy Investigation of Insect Wings Tegan Shiver, Carlos Lawhead, Josiah Anderson, Nathan Cooper, Laszlo Ujj Measuring the surface morphology and chemical composition of insect wings is important to understand the extreme mechanical properties and the biophysical functionalities of the wings. We have measured the image of the membrane of the cicada (genus \textit{Tibicen}) wing with the help of Scanning Electron Microscopy (SEM). The results confirm the existing periodic structure of the wing measured previously [1]. The SEM imaging can be used to measure the surface morphology of any insect species wings. The physical surface structure of the cicada wing is an example of a new class of biomaterials that can kill bacteria on contact [2]. In order to identify the chemical composition of the wing, we have measured the vibrational spectra of the wing's membrane (Raman and CARS). The measured spectra are consistent with the original assumption that the wing membrane is composed of protein, wax, and chitin [2]. The results of these studies can be used to make artificial materials in the future.\\[4pt] [1] Mark J. Tobin, et al. ``High-spatial-resolution mapping of superhydrophobic cicada wing surface chemistry using infrared microspectroscopy and infrared imaging at two synchrotron beamlines'' Journal of Synchrotron Radiation vol. 20 pp. 482-489 2013\\[0pt] [2] Sergey Pogodin, et al. ``Biophysical Model of Bacterial Cell Interactions with Nanopatterned Cicada Wing Surfaces'' Biophysical Journal vol. 104 pp. 835-840 2013 [Preview Abstract] |
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H1.00054: Progress towards a dense atomic beam Martin Disla, Brian Kaufman, Matthew Wright We are constructing a dense atomic beam source of Rb atoms that operates from 300 K to 600 K. We have designed the apparatus to access the high density region in the beam immediately after exiting the oven. Initial heating tests in vacuum confirmed that we will able to access the desired temperature range. We will add atomic Rb to the oven and measure its density as a function of temperature using spectroscopy. [Preview Abstract] |
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H1.00055: The Young Solar Analogs Project Ryan Lambert, Richard Gray The ultimate goal of the Young Solar Analogs Project is to give insight into the conditions in the early solar system when life was first forming on the earth and to assess the challenges the young, active sun presented to that early life. To achieve this, we have been monitoring since 2007 the stellar activity of 31 young solar-type stars with ages between 0.3 and 1.5 Gyrs. Many of these stars exhibit star spot cycles like the sun, but in a few cases we are seeing evidence for a previously unknown type of star spot cycle. Some vary chaotically. We have detected the presence of differential rotation in several stars. We have also detected a number of powerful flares both photometrically and spectroscopically. Optical irradiance changes in these stars can be as high as 10{\%} in a single year; such solar variability would have led to catastropic climate change on the early earth. [Preview Abstract] |
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H1.00056: Unconventional nuclear magnetic resonance techniques using nanostructured diamond surfaces Victor Acosta, Andrey Jarmola, Dmitry Budker, Charles Santori, Zhihong Huang, Raymond Beausoleil Nuclear magnetic resonance (NMR) technologies rely on obtaining high nuclear magnetization, motivating low operating temperatures and high magnetic fields. Dynamic nuclear polarization (DNP) techniques traditionally require another superconducting magnet and THz optics. We seek to use chip-scale devices to polarize nuclei in liquids at room temperature. The technique relies on optical pumping of nitrogen-vacancy (NV) centers and subsequent transfer of polarization to nuclei via hyperfine interaction, spin diffusion, and heteronuclear polarization transfer. We expect efficient polarization transfer will be realized by maximizing the diamond surface area. We have fabricated densely-packed (50$\%$ packing fraction), high-aspect-ratio (10+) nanopillars over mm$^2$ regions of the diamond surface. Pillars designed to have a few-hundred-nanometer diameter act as optical antennas, reducing saturation intensity. We also report progress in using nanopillar arrays as sensitive optical detectors of nano-scale NMR by measuring NV center Zeeman shifts produced by nearby external nuclei. The enhanced surface area increases the effective density of NV centers which couple to external nuclei. Combining these techniques may enable, e.g., identification of trace analytes and molecular imaging. [Preview Abstract] |
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H1.00057: Progress toward injection locking a 795 nm diode laser to a microwave modulated sideband John Dellatto, Martin Disla, Brian Kaufman, Kevin Teng, Anthony Limani, Matthew Wright Light from an external-cavity diode laser is locked to an external frequency reference, is passed through an electro-optic phase modulator, and is used to injection-lock a free running diode laser. The resulting power of the injection-locked laser is 200mW. We have generated sidebands from 3GHz to 7GHz and will discuss how the amplitude of the sidebands depends on the power of the microwave signal. We will also discuss our progress toward injection-locking to one of the sidebands. [Preview Abstract] |
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H1.00058: Characterization and calibration of a combined laser Raman, fluorescence and coherent Raman spectrometer Carlos Lawhead, Nathan Cooper, Josiah Anderson, Tegan Shiver, Laszlo Ujj Electronic and vibrational spectroscopy is extremely important tools used in material characterization; therefore a table-top laser spectrometer system was built in the spectroscopy lab at the UWF physics department. The system is based upon an injection seeded nanosecond Nd:YAG Laser. The second and the third harmonics of the fundamental 1064 nm radiation are used to generate Raman and fluorescence spectra measured with MS260i imaging spectrograph occupied with a CCD detector and cooled to -85 $^{\circ}$C, in order to minimize the dark background noise. The wavelength calibration was performed with the emission spectra of standard gas-discharge lamps [1]. Spectral sensitivity calibration is needed before any spectra are recorded, because of the table-top nature of the instrument. A variety of intensity standards were investigated to find standards suitable for our table top setup that do not change the geometry of the system. High quality measurement of Raman standards where analyzed to test spectral corrections. Background fluorescence removal methods were used to improve Raman signal intensity reading on highly fluorescent molecules. This instrument will be used to measure vibrational and electronic spectra of biological molecules. \\[4pt] [1] Carrabba, M. ``Wavenumber Standards for Raman Spectrometry'' \textbf{Handbook of Vibrational Spectroscopy}. John Wiley {\&} Ltd. 2002. [Preview Abstract] |
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H1.00059: Laser Station Design for the Global Light System for the Planned JEM-EUSO Extreme Universe Observatory Christine Geier, Martin Burg, Colton Bigler, Lawrence Wiencke The JEM-EUSO Global Light System (GLS) will provide ground-based calibration and monitoring for the JEM-EUSO detector planned for the International Space Station (ISS). JEM-EUSO will use the atmosphere as a giant calorimeter to measure Ultra High Energy Cosmic Rays (UHECRs). The GLS will include twelve ground stations. All twelve will have calibration xenon flash bulbs and six will have steered lasers. The GLS laser stations will generate optical signatures by creating light tracks across the JEM-EUSO field of view. The lasers and xenon flashers will be used to benchmark the JEM-EUSO instrument during its mission since energy, duration and orientation of those sources can be controlled. In this presentation, we will describe a project to design and build a working prototype of a GLS laser station. In order to meet the specifications set forth in the design requirements, our design incorporates remote operation capability, solar power, and a controlled internal climate. These components are in addition to the laser and calibration system and steering mechanism. All components will be combined in a robust, durable design that can be deployed and operated in remote locations across the globe. [Preview Abstract] |
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H1.00060: Toxicological Effects of Fullerenes on \textit{Caenorhabditis elegans} Justin Schomaker, Renee Snook, Carina Howell The nematode species \textit{Caenorhabditis elegans} is a useful genetic model organism due to its simplicity and the substantial molecular, genetic, and developmental knowledge about the species. In this study, this species was used to test the toxicological effects of C60 fullerene nanoparticles. In previous studies using rats, a solution of C60 fullerenes in olive oil proved to extend the life of the subjects. The purpose of this experiment was to subject \textit{C. elegans} to varying concentrations of C60 fullerenes and observe their toxicological effects. Initial findings indicate a link between fullerene exposure and enlargement of the vulva as well as the formation of a small nodule at the base of the tail in some individuals. While the fullerenes are not lethally toxic in C. elegans, results will be presented that pertain to changes in life span and progeny of the nematodes exposed to varying concentrations of fullerenes as well as the mechanisms of toxicity. High magnification imaging via SEM and/or AFM will be used to characterize the fullerene nanoparticles. Testing the toxicity of fullerenes in a wide variety of organisms will lead to a more complete understanding of the effects of fullerenes on living organisms to ultimately understand their effects in humans. [Preview Abstract] |
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H1.00061: Direct CVD Growth of Monolayer Graphene on Exfoliated BN on SiO$_{2}$ Han Sae Jung, Hsin-Zon Tsai, Erik Piatti, Kacey Meaker, Jairo Velasco, Alex Zettl, Michael Crommie Graphene on BN exhibits exceptionally high charge carrier mobility, which makes it promising for future device applications. However, current CVD methods of growing graphene on a catalytic metal surface require a chemical transfer process onto BN substrate, which introduces polymers and etchants that can contaminate the surface of pristine graphene. Here, we present a method for directly growing graphene on BN, a non-catalytic surface. This method not only eliminates the undesirable transfer process, but also successfully grows clean graphene with well-defined edges. We performed Raman spectroscopy and atomic force microscopy, which showed a high coverage of monolayer graphene with low D peak and single hexagonal graphene domains of sub-micron size. [Preview Abstract] |
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H1.00062: Characterization of Mixed Polypeptide Colloidal Particles by Light Scattering Hannah E. Shuman, Grace K. Gaeckle, John Gavin, Nolan B. Holland, Kiril A. Streletzky Temperature-dependent polymer surfactants have been developed by connecting three elastin-like polypeptide (ELP) chains to a charged protein domain (foldon), forming a three-armed star polymer. At low temperatures the polymer is soluble, while at higher temperatures it forms micelles. The behavior of mixtures of the three-armed star ELP (E20-Foldon) and H40-Linear ELP chains was analyzed under different salt and protein concentrations and various foldon to linear ELP ratio using Depolarized Dynamic Light Scattering. It was expected that under certain conditions the pure E20-Foldon would form spherical micelles, which upon adding the linear ELP would change in size and possibly shape. The pure E20-Foldon indeed formed largely spherical micelles with R$_{\mathrm{h}}$ of 10-20nm in solutions with 15-100mM salt and protein concentration between 10$\mu $M and 100$\mu $M. For the mixtures of 50$\mu $M E20-Foldon and varying concentrations of H40-Linear in 25mM of salt, it was discovered that low and high H40-Linear concentration (4$\mu $M and 50$\mu $M) had only one transition. For the mixtures with of 10 and 25$\mu $M of H40-Linear the two distinct transition temperatures were observed by spectrophotometry. The first transition corresponded to significantly elongated diffusive particles of apparent R$_{\mathrm{h}}$ of 30-50nm, while the second transition corresponded to slightly anisotropic diffusive particles with apparent R$_{\mathrm{h}}$ of about 20nm. At all H40-Linear concentrations studied, diffusive particles were seen above the second transition. Their radius and ability to depolarize light increased with the increase of H40-Linear concentration. [Preview Abstract] |
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H1.00063: Polarization Sensitive Coherent Raman Measurements of DCVJ Josiah Anderson, Nathan Cooper, Carlos Lawhead, Tegan Shiver, Laszlo Ujj Coherent Raman spectroscopy which recently developed into coherent Raman microscopy has been used to produce label free imaging of thin layers of material and find the spatial distributions of certain chemicals within samples, e.g. cancer cells.(1) Not all aspects of coherent scattering have been used for imaging. Among those for example are special polarization sensitive measurements. Therefore we have investigated the properties of polarization sensitive CARS spectra of a highly fluorescent molecule, DCVJ.(2) Spectra has been recorded by using parallel polarized and perpendicular polarized excitations. A special polarization arrangement was developed to suppress the non-resonant background scattering from the sample. These results can be used to improve the imaging properties of a coherent Raman microscope in the future. This is the first time coherent Raman polarization sensitive measurements have been used to characterize the vibrational modes of DCVJ. 1: K. I. Gutkowski, et al., ``Fluorescence of dicyanovinyl julolidine in a room temperature ionic liquid '' \textbf{Chemical Physics Letters 426 (2006) 329 -- 333} 2: Fouad El-Diasty, ``Coherent anti-Stokes Raman scattering: Spectroscopy and microscopy'' \textbf{Vibrational Spectroscopy 55 (2011) 1-37} [Preview Abstract] |
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H1.00064: Mitochondrial Insult in a Parkinson's like symptoms model Julio Carrizales, Manuel Cantu, Daniel Plas Healthy cells require healthy mitochondria. If these organelles are damaged, many health consequences follow. For example, Parkinson's Disease (PD) is a major neurodegenerative disorder of unknown cause, but much evidence points to the mitochondrion as a key player in the onset of this disease. PD has been studied in animal models challenged with toxins that target the mitochondria. In our work, we have used the pesticide, Rotenone, a known inhibitor of protein Complex I in the mitochondrial electron transport chain. When this toxin is applied to the freshwater mollusk, Lymnaea stagnalis, or pond snail, severe motor deficits ensue. In this project, we are studying the direct effects of this toxin on mitochondrial structure and physiology. We expected that the morphology of the organelle may be altered. In addition, it is likely that the mitochondrial membrane potential necessary for normal function may decrease as the electron transport loses the ability to move protons from the matrix to the intermembrane space. we also are going to use Electrophysiology to compare and Identify the difference of the electrical signaling among healthy and unhealthy neurons. [Preview Abstract] |
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H1.00065: Silicon Nitride Diffraction Gratings On Platinum TEM Apertures Alexander Schachtner, Jordan Pierce, Tyler Harvey, Jordan Chess, Tyler Yahn, Benjamin McMorran We use focused ion beam (FIB) nanofabrication to manufacture forked diffraction gratings capable of producing electron beams with helical wavefronts and orbital angular momentum (OAM). A vast number of unique beam modes carrying OAM can be produced through manipulation of grating fork number or position. Generally these gratings are milled such that they produce a phase shift in the beam and are used with high energy electrons (300keV) in a TEM to investigate the quantum or magnetic properties of the electron or image magnetic materials. Our latest work outlines an attempt to adhere these diffraction gratings, milled on silicon nitride membranes via FIB, to platinum SEM and TEM apertures in an effort to facilitate novel materials imaging capabilities as well as establish a long-term installation method. Methods for membrane-aperture adhesion are presented, as well as the diffraction grating production that takes place post-adhesion. [Preview Abstract] |
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H1.00066: A Matter of Energy Efficiency: From Modeling Falling Raindrops to Controlling Rocket Thrust Eric Harding A power-law accretion model is used to investigate the energy dynamics of a falling raindrop in a Newtonian gravitational field where air resistance is included in the analysis. This model is seen to be related to the rate of ejection of exhaust gases for the rocket problem. Energy analysis of the falling raindrop will be presented for the motion of very small droplets, those of diameter less than 0.003 inches, which are falling at relatively slow speeds, of less than 0.188 m/s. The deviation from self-similar accretion, and other relevant model parameters will be re-interpreted as related to control parameters in the rocket problem. Efficiency of natural energy transfer for the falling raindrop will be compared with the power transfer model for the rocket. [Preview Abstract] |
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H1.00067: ABSTRACT WITHDRAWN |
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H1.00068: Role of Contacts in Capacitance Measurements of Solar Cells Justin Davis, James Harger, Addison Wisthoff, Jennifer Heath The electronic properties of low cost, thin-film solar cells are complicated by the non-ideal nature of the semiconductor layers. Typically, the fundamental electronic properties of such materials are evaluated using current-voltage and capacitance-voltage measurements. However, in these devices, it is common for the back contact to be non-ohmic. We are exploring the impact of such a back contact on the outcome of standard capacitance-based characterization techniques. We compare computer models of capacitance response with measurements of simple model electronic circuits, and of solar cell devices. [Preview Abstract] |
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H1.00069: The Effect of Nonlinearity on Topological States in Quasiperiodic Lattices Phong Vo, Yoav Lahini The discovery of topological insulators has sparked considerable interest in the study of topological phases of matter. Recently, it has been shown that certain quasiperiodic systems are also topologically nontrivial. As topological states arise from a linear, non-interacting theory of solids, it is of interest to understand the effect of interactions on topological properties. In an extensive numerical study, we introduce nonlinearity into a 1-D quasiperiodic model to observe its effect on energy localization at the boundary due to topological edge states. We compare two different quasiperiodic modulations: one where the on-site potential is modulated at an incommensurate frequency (the diagonal Aubry-Andre model), and a second in which the hopping terms are modulated (off-diagonal model). We find that in the diagonal model, increasing the magnitude of nonlinearity delocalizes energy from the boundary. The strength of nonlinearity needed for delocalization depends on the eigenvalue of the linear edge state, the width of the gap in which it resides, and the sign of nonlinearity. In contrast, in the off-diagonal model, the effects of positive and negative nonlinearity are identical when only the edge lattice site is excited due to symmetry in the eigenvalue spectrum. [Preview Abstract] |
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H1.00070: CVD Grown Graphene for Gas Detectors Andrew Tan, Christina Bibler, Michael Crosser The so-called scotch-tape method is a commonly used process to isolate graphene from bulk graphite. However, the flakes of graphene that are produced are small and must be found individually. We present results from our home-built chemical vapor deposition chamber that allow us to produce large surface graphene sheets via the pyrolytic decomposition of methane. We also present ongoing work to produce devices from this graphene for the purpose of making gas sensors. [Preview Abstract] |
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H1.00071: Polarization Sensitive Measurements of Molecular Reorientation in a Glass Capacitor Cell Nathan Cooper, Carlos Lawhead, Josiah Anderson, Tegan Shiver, Chandra Prayaga, Laszlo Ujj It is well known that molecules having a permanent dipole moment tend to orient in the direction of the electric field at room temperature. The reorientation can be probed with the help of linear spectroscopy methods such as fluorescence anisotropy measurements. We have used nonlinear polarization sensitive Raman scattering spectroscopy [1] to quantify the orientation effect of the dipoles. Vibrational spectra of the molecules has been recorded as a function of the external electric field. The polarization changes observed during the measurement are directly linked to the molecular reorientation rearrangement. Spectra has been recorded with a laser spectrometer comprised of a Nd:YAG laser and an optical parametric oscillator and an imaging spectrometer with a CCD detector. In order to make this measurement we have constructed a glass capacitor cell coated in TiO and applied a significant electric field (0-3 kV/mm) to the sample. Our measurements showed that the orientation effect is most significant for liquid crystals as observed previously with non-polarization sensitive CARS spectroscopy [2]. Reference: 1. El-Diasty, F. `Coherent anti-Stokes Raman scattering: Spectroscopy and microscopy'' Vibrational Spectroscopy 55 (2011) 1-37. 2. Kachynski, A., et al. ``Realignment-enhanced coherent anti-Stokes Raman scattering (CARS) and three-dimensional imaging in anisotropic fluids'' Opt. Express (2008). [Preview Abstract] |
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H1.00072: ABSTRACT WITHDRAWN |
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H1.00073: Do lattice protein simulations exhibit self-organized criticality? Addison Wisthoff, Joelle Murray Proteins are known to fold into tertiary structures that determine their functionality in living organisms. The goal of my research is to better understand the protein folding process through a lattice Monte-Carlo simulation. Specifically, amino acids in the chain at each time step are allowed to fold to certain locations according to two main criteria: folds must maintain bond length and should be thermally and energetically favorable. This simulation will then be used to examine whether the folding process can be viewed through the lens of self-organized criticality (SOC). In particular I am interested in whether there are features of the folding process that are independent of the size of the protein. [Preview Abstract] |
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H1.00074: Potential Wells and the Generalized Uncertainty Principle Constance Owens, Gardo Blado, Vincent Meyers Out of the four fundamental forces, we have yet to be able to unify gravity with the other three forces. This predicament has kept scientists from being able to explain systems that use both general relativity (GR) and quantum mechanics (QM). The quest to quantize gravity, in other words to make GR a quantum theory, has been at the forefront of physics research in recent decades. Incorporating gravity into QM changes the laws of ordinary quantum mechanics. Potential wells are a common tool used to study particle behavior in quantum mechanics. At first they were simply theoretical toy models, but within time it was discovered that potential wells could actually be used to model real-life situations and thus have proven to be very useful theoretically and experimentally. For example, the double square well (DSW) can be used to model the potential experienced by an electron in a diatomic molecule. DSWs can also be used to study bilayer systems. In this paper we derive the results for the finite square well and the DSW using a form of the generalized uncertainty principle to study and discuss how the incorporation of gravity modifies these results. We also discuss applications and the effects of gravity on quantum tunneling. [Preview Abstract] |
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H1.00075: Zinc Oxide Nanowire Capture of Silicon Quantum Dots Leah Moldauer, Ben Schoh A zinc oxide nanowire array is being fabricated to capture silicon quantum dots synthesized using a gas-phase process. There may be a variation of dot diameter when dots are deposited on a planar surface which is not apparent due to dot mixing. By using the nanowire array to trap the dots, a model can be developed to describe the variations in dot diameter. The nanowire, quantum dot hybrid device will be characterized using spectroscopy and possible applications of the device will be explored. [Preview Abstract] |
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H1.00076: Self-organized criticality of protein folding simulations using AMBER parameters Yura Sim, Joelle Murray Self-organized criticality is a framework that can be used to describe many natural processes, ranging from avalanches to forest fires. These processes exhibit power-law characteristics and scale invariance. Self-organized critical systems have yet to be applied to protein folding and its identification as such may be useful to understanding protein behavior. A dynamical simulation was constructed using AMBER energy parameters and evidence of self-organized criticality was investigated. Furthermore, the features of self-organized criticality were used to explore the development of protein structures within the simulation. [Preview Abstract] |
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H1.00077: Structure and phase behavior of colloidal hard dumbbells under the influence of gravity Matthew Wozniak, Manuel Valera Using molecular dynamics simulations, we studythe structureofsystems of hard dumbbell particles that are sedimented under the influence of gravity. It is useful to determine these structural measures with agravitational field because of recent experimental interest in systems of colloidal dumbbells, which are massive enough that settling effects must be taken into account. Similar studies[M. Marechal and M. Dijkstra, \textit{Soft Matter}, 2011, 7, p.1397-1408] have used Monte Carlo simulations to provide information about structural and phase characteristics that develop in a gravitational field for systems of dumbbell particles of multiple aspect ratios. However, it has not yet been determined for dumbbell particles how crystal growth and the phase behavior of the systemareeffectedby the strengthening of the gravitational field. In this research, the structure and phase behavior of systems withdifferent gravitational strengths and dumbbell aspect ratios are visualized and quantified. [Preview Abstract] |
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H1.00078: Analysis Methods for Frequency Resolved Florescence Anisotropy Studies Sam Migirditch, Jacob Cole, Tyler Foley, Brooke Hester Fluorescence is a phenomenon for which scientific tools have been developed with many diverse methods for extracting information from complex systems. One of these methods utilizes the examination of the anisotropy $r$, correlation time $\theta $, and decay $\tau $ of the fluorophore. Here we develop computational techniques for analyzing experimental data acquired from decaying fluorophores. Using data from a frequency resolved decay of a fluorophore and an expected curve based on our model we use a standard least squares approach to curve fitting by adjusting the parameters in the model while seeking to reduce the sum of the squares of the error from fitting. In addition to the fundamental properties mentioned, we can also learn information about the physical state of a complex microscopic system with a bound fluorophore. Our analysis technique is tested by comparing the results against the results from previous experiments for well-studied fluorophores. [Preview Abstract] |
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H1.00079: Symmetry methods for five bodies in a one-dimensional harmonic trap Jennifer Verniero, Nathan Harshman, Joshua Lansky We present a method of studying few body systems of five particles in a one-dimensional harmonic trap. This model exhibits a simple but rich mathematical structure that allows us to explore the relationships among symmetry, integrability, and entanglement for cold atoms in an optical well. In particular, calculations are simplified by exploiting the S$_{5}$ permutation symmetry of the system. The ramifications of this symmetry are investigated using methods of Young Tableaux to construct irreducible representations and basis vectors. The group S$_{5}$ is unsolvable and not simply reducible and that distinguishes the five body case as qualitatively more complex than fewer bodies. This complexity in the energy and entanglement spectra offers novel prospects for quantum information encoding. [Preview Abstract] |
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H1.00080: Optimized basis transformations for the symmetrization of a few ultra-cold atoms in a harmonic trap Jarrett Revels, N.L. Harshman Motivated by applications to ultra-cold atomic systems, we present a memoized algorithm for calculating basis transformation coefficients in the case of N-particles in a D-dimensional harmonic trap. Such coefficients are useful in the construction of symmetrized bases. These bases exploit invariance to allow for the efficient calculation of energy and entanglement spectra. Our algorithm utilizes creation and annihilation operators to algebraically construct transformation coefficients of higher excitation subspaces from lower excitation subspaces. As an example, we use these coefficients to compare the entanglement of a fermionic system with a bosonic system that has been fermionized due to strongly repulsive interactions. [Preview Abstract] |
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H1.00081: ENERGY RESEARCH AND APPLICATIONS |
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H1.00082: Imagine a Dream of Love, Ripple Jerry A. (Tony) Witt MATH 1st, $Mc^2/r^2=E/r=2/.5=1<3$, ($<3$) is a heart (feelings matter, thanks!). this equation shows that or 3 dimensional universe is also the singularity enfold(ed)ing and unfold(ed)ing unto itself. (c$^2$) needing space being rate is distance distance over time, also a square being a flat surface of no depth would make the universe which has a mass flat in all directions simultaneously quantum (G) I believe. (r) being half distance would illustrate a double inversion being $2+1=3$, as in dimensional reality. A double inverse expressing a reverse, thus Verlinde's principal should be a simple law rather than a question. Equal and opposite forces cancelling, motion requiring initial force all points connected as a singularity as well as dimensional cancelling one another out as well as fueling motion, as supported by Doug Singleton's, Perpetuum Mobile paper. bringing into question thermodynamic laws heat more likely exhausted energy, motion rate being a matter of relative energy use as well as rate in accordance with Verlinde's and Singleton's works (thanks and thanks again Doug). I should mention Hawking and Al are two of the funnest guys ever, physics is phun. [Preview Abstract] |
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H1.00083: Structural Changes Driven by Li Flux Density in Initial Lithiation of Single Crystal Silicon Li-Qiong Wang, Myeonghun Song, Siva Nadimpalli, Pradeep Guduru, Vijay Sethuraman, Michael Chon Structural changes in amorphous Li$_{\mathrm{x}}$Si were investigated as a function of Li flux density and total charge in the initial lithiation of single crystal (100) Si wafers using solid-state $^{7}$Li nuclear magnetic resonance (NMR) spectroscopy. We chose a single crystal Si wafer as a model system in this study because of well-controlled Li flux density uniformly distributed across the surface of a silicon wafer. In contrast to a widely accepted Li$_{3.5}$Si structure for the initial lithiation, this study shows a surprising finding of varying Li$_{\mathrm{x}}$Si structures that are controlled by the Li flux density but not by the total charge. In particular, we discovered that the rate constant and the reaction mechanism at the reaction front depend on the Li flux density. The previous kinetic model is required to include the Li flux density dependent rate constant to accurately describe the reaction front kinetics in the initial lithiation of crystalline silicon. Our study provides new insight toward the understanding of the kinetics, the reaction mechanisms, and the kinetic modeling of chemical reactions at the reaction front. [Preview Abstract] |
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H1.00084: Coating mechanism of polybenzoxazine onto tubular alumina support for ethanol-water separation Sujitra Wongkasemjit, Panupong Chuntanalerg, Ni-on Saelim, Santi Kulthippanja, Thanyalak Chaisuwan Tubular $\alpha $-Al$_{2}$O$_{3}$ supported polybenzoxazine (PBZ) membranes were prepared by dip-coating technique for ethanol-water separation via pervaporation. The effect of PBZ concentration on number of dipping cycle requirement and separation performance was studied. Based on the obtained results, a possible mechanism of the membrane formation was investigated and proposed. It was founded that two membrane preparation steps were involved, viz. transition layer accumulation and layer formation. The membrane prepared by using 25 wt{\%} PBZ needed the shortest preparation time and provided the highest separation factor. Moreover, the prepared membrane had excellent stability in every feed ethanol concentration with the separation factor higher than 10,000. The study of a long-term pervaporation in 90:10 ethanol:water feed was also carried out and the results showed the excellent durability during 11 days of operation with 99.45 wt{\%} of ethanol.. [Preview Abstract] |
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H1.00085: Initial Decomposition Mechanism study for the Energy Release from Electronical Excited Energetic Material Bing Yuan Decomposition of energetic materials FOX-7 and 3,4-dinitropyrazole (DNP) are investigated both theoretically and experimentally. The two energetic model systems 1-nitropyrazole and 4-nitropyrazole are also studied as a comparison for DNP. The NO molecule is observed as an initial decomposition product from all four materials subsequent to UV excitation and the observed NO products are rotationally cold ($<$ 50 K). The vibrational temperature of the NO product from DNP is 3300 K, 1400 K hotter than that of its model species. The vibrational temperature of the NO product from FOX-7 is 1900 K. The initial decomposition mechanisms of these materials are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface (PES) calculations at the CASSCF(12,8)/6-31+G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S2 molecules can nonradiatively relax to lower electronic states through (S2/S1)CI and (S1/S0)CI conical intersections and undergo a nitro-nitrite isomerization to generate an NO product either on the S1 state or S0 state PES. For model systems, NO is generated on the S1 state PES, while for the energetic materials FOX-7 and DNP, NO is produced on the ground state PES, [Preview Abstract] |
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H1.00086: Al-Modified SiCN Carbon Nanotube Coatings as Lithium ion Battery Electrode Lamuel David, Deepu Asok, Gurpreet Singh Aluminium modified poly(ureamethylvinyl)silazane were blended with carbon nanotubes and pyrolyzed to synthesize SiAlCN-CNT composite. The structural and chemical characterization of the composite prepared were carried out using electron microscopy, XRD, and FT-infrared spectroscopy. The SiAlCN-CNT composite anodes showed stable charge capacity of 850 mAh/g at 100 mA/g and 550 mAh/g even at high current density of 10000 mA/g. The average columbic efficiency (second cycle onwards) was observed to be approx. 99{\%}. [Preview Abstract] |
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H1.00087: First-principle study of thermoelectric properties of impurity-doped magnesium silicide Mg2Si Hiroki Funashima The electronic structure and the thermoelectric properties of Mg$_2$Si doped with several dopants, Al, Bi, Sb, and Zn, are theoretically examined using a first-principles calculation method. Mg$_2$Si is a promising thermoelectric material that is functional in the temperature range from 500 to 800 K. Therefore, it is expected to be useful for recovering waste heat from exhaust gas in automotive applications, incinerators, and boilers. Moreover, this material has several desirable attributes with respect to cost and environmental protection: it is cheap, nontoxic, and composed of elements abundant on Earth. These advantages are important for practical usage in thermoelectric applications. Impurity doping is a well-established way to improve the thermoelectric performance of Mg$_2$Si. Undoped Mg$_2$Si crystals have n-type conductivity, but they can be doped with both n- and p-type impurities. A fundamental understanding of the relationship between impurity doping and the thermoelectric properties of Mg$_2$Si will allow us to provide theoretical guidelines for further development of this material. As an effort toward this goal, we present here the band structure of Mg$_2$Si using the full-potential linearized augmented plane-wave (FLAPW) method based on LDA/DFT and the conductivity. [Preview Abstract] |
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H1.00088: Understanding Thermal Conductivity in Amorphous Materials Sampath Kommandur, Shannon Yee Current energy technologies such as thermoelectrics, photovoltaics, and LEDs make extensive use of amorphous materials and are limited by heat transfer. Device improvements necessitate a better understanding of the thermal conductivity in amorphous materials. While there are basic theories that capture the trends in thermal conductivity of a select set of amorphous materials, a general framework is needed to explain the fundamental transport of heat in all amorphous materials. One empirical theory that has been successful at describing the thermal conductivity in some materials is the k-min model, however, assumptions in that model limit its generalizability. Another theory defines the existence of propagons, diffusons, and locons, which constitute vibrational modes that carry heat. Our work first presents a summary of literature on the thermal conductivity in amorphous materials and then compares those theories to a breadth of experimental data. Based upon those results, a generic model is proposed that is widely applicable with the ultimate goal of this work being to describe the temperature dependent thermal conductivity of polymers. -/abstract- Sampath Kommandur and Shannon K. Yee 21.1.1: Thermoelectric Phenomena, Materials, Devices, and Applications (GER [Preview Abstract] |
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H1.00089: Thermoelectric properties of ZnO under high pressure: a first-principles study Andrew Alvarado, Jeevake Attapattu, Yi Zhang, Changfeng Chen ZnO is a very important semiconducting material that exhibits interesting physical properties with great promise for applications in electronic and optical devices. A recent study predicted that ZnO may be a viable high-temperature thermoelectric material at ambient pressure. There is, however, a lack of understanding of the thermoelectric properties of its high pressure phases. Here we report our first-principles studies of thermodynamic and thermoelectric properties of wurtzite, zinc-blended, and rocksalt phases of ZnO. Using the Boltzmann transport theory, we obtained the dependence of the figure of merit ZT on doping and temperature. Our results establish the quenchable high-pressure ZnO phase as a promising high-temperature thermoelectric material. [Preview Abstract] |
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H1.00090: Local and Intermediate Range Structure of Thermoelectric Ca$_{3}$Co$_{4}$O$_{9}$ Trevor Tyson, Tao Wu, Tian Yu, Milinda Abeykoon The detailed local and intermediate range structure of thermoelectric Ca$_{3}$Co$_{4}$O$_{4}$ has been examined. X-ray absorption spectroscopy has been to explore the structure about the Co, Ca and O sites. Detailed short and intermediate structural studies by x-ray PDF measurements are used to explore the structure over a broad range of temperatures. The connection of structure with observed physical properties is discussed. [Preview Abstract] |
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H1.00091: Design of a Polymer-Based Radial Thermoelectric Generator Akanksha Menon, Shannon Yee Polymers possess desirable properties such as low thermal conductivity, low cost, and scalable processability as compared to inorganic materials. These characteristics make polymers attractive for thermoelectric (TE) applications. Current examples of polymer thin-film TE devices are limited to traditional rectangular/parallel plate geometries. The focus of this work is to investigate the effect of radial device geometry on TE performance. Each TE module consists of many divided discs of p- and n-type polymers on a thermally insulating circular substrate. In the center of the disc a channel of warm fluid flows as the source of heat, which creates a radial temperature gradient across the TE. Many discs can be stacked and connected electrically in series, thus generating an appreciable output voltage. In this work, analytic thermal and electrical models are developed to present an optimized device geometry for maximum power, maximum efficiency, and low {\$}/W scenarios. While the efficiency equation is identical to that for a rectangular geometry, the non-linear resistance of the radial device offers a higher power density and greater thermal insulation than traditional rectangular TEs. [Preview Abstract] |
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H1.00092: Thermally-Active Screw Dislocations in Si Nanowires and Nanotubes Traian Dumitrica, Shiyun Xiong, Jihong Ma, Sebastian Volz New properties appear when nanomaterials contain dislocations. Understanding whether these features, which arise naturally during growth, are beneficial or problematic becomes essential for developing applications. Here we investigate 110 Si nanowire and nanotube structures containing an axial screw dislocation, as described by objective molecular dynamics coupled with the classical Tersoff potential. By means of direct nonequilibrium molecular dynamics simulations, we uncover significant reductions in thermal conductivity when nanostructures contain axial screw dislocations with closed and open cores. Analysis based on the atomistic Green function method reveals that in nanowires, the effect originates largely in the phonon-phonon scattering due to the enhanced anharmonicity introduced by highly distorted core region of the dislocation. In nanotubes, the inner surface compensates effectively for the missing core region. The uncovered effect can act in combination with other already known thermal conductivity limiting mechanisms, and thus can enable the further optimization of the figure of merit for a new family of complex thermoelectric nanomaterials. [Preview Abstract] |
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H1.00093: Gap States at the Organic Semiconductor / Oxide Interface: Control of Energy Level Alignment Oliver Monti, Leah Kelly, Philip Schulz, David Racke, Antoine Kahn We show by means of core level, valence band and inverse photoemission spectroscopy as well as computational modeling that states inside the oxide bandgap fundamentally determine energy level alignment and electronic structure on the electron collection interface in an organic photovoltaic cell. We investigate the prototypical interface of C$_{\mathrm{60}}$ on thin, highly conductive ZnO films and demonstrate that defect states introduced selectively into ZnO can radically alter energy level alignment at this interface. As a result, injection barriers can be selectively introduced, with direct consequences for the current-voltage properties of a device built from C$_{\mathrm{60}}$ and ZnO. Our results show unambiguously that interfacial energy level alignment at organic / oxide interfaces is determined by fundamentally different physics from the more studied metal / organic interfaces, and demonstrate new avenues of controlling injection barriers and dynamics. [Preview Abstract] |
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H1.00094: Free carrier lifetime determination using time-resolved microwave conductivity: methods and implications for devices Stefan Oosterhout, Zbyslaw Owczarczyk, Wade Braunecker, Nikos Kopidakis, Ross Larsen, David Ginley, Dana Olson Optimizing devices for high performance is a time consuming, tedious task. Many polymers that have been synthesized over the last decade, have been employed in devices and proved to have a low power conversion efficiency only after a tedious device optimization experiment. A good free carrier lifetime in polymer organic photovoltaic devices is essential for decent device performance. This characteristic of polymer donor and fullerene acceptor bulk heterojunctions can be determined prior to device fabrication using the contactless time-resolved microwave conductivity (TRMC), eliminating the need for time-consuming device optimization experiments when the free carrier lifetime is low. This presentation focuses on how TRMC is utilized for screening potential new materials for OPV, and methods for a figure-of-merit for charge carrier lifetime is discussed. [Preview Abstract] |
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H1.00095: Fabrication and study of organic solar cells composed of P3HT/PCBM blend with monolayers of P(VDF-TrFE) Hector Carrasco, Josee Vedrine Organic polymeric materials that are conducting provide an added facility in device fabrication, particularly in solar cell applications. In this work, we study the electrical and morphological properties of bulk hetero-junction solar cells fabricated with poly (3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric-acid-methyl ester (PCBM) blends, when a monolayer of the ferroelectric polymer poly[(vinylidenefluoride-co-trifluoroethylene] [P(VDF-TrFE)] is deposited between ITO conductor and bulk heterojunction. The bulk heterojunction and ferroelectric films are annealed at 140 $^{\circ}$C under vacuum atmosphere to improve their crystallinity, which may assist in enhanced charge transfer. We measure device photovoltaic properties with changing blend thickness, while keeping the ferroelectric layer constant.. The current-voltage characteristics are measured and compared for the different film thicknesses. AFM techniques are used to analyze their morphological and conductive properties. [Preview Abstract] |
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H1.00096: SiBCN-CNT/Graphene Paper Electrode Lamuel David, Gurpreet Singh We demonstrate synthesis and electrochemical performance of novel molecular precursor-derived ceramic (PDC)/carbon nanotube embedded graphene self-supporting composite papers as Li-ion battery electrode. The papers were prepared through vacuum filtration of various PDC-graphene oxide (GO) dispersions in DI water followed by thermal reduction at elevated temperatures that resulted in a homogenous PDC/reduced GO papers that were highly crumpled, mechanically robust and consisted of a 3-D electrically conducting network. These electrodes showed electrochemical capacities as much as approx. 300 mAh.g$^{\mathrm{-1}}$ with respect to total weight of the electrode (approx. 500 mAh.g$^{\mathrm{-1}}$ w.r.t. active material), with negligible capacity loss for more than 1000 cycles. Boron-doped silicon carbon nitride (Si(B)CN/graphene) outperformed its un-doped counterparts (SiCN/graphene), both in terms of electrochemical capacity, cycling stability and coulombic efficiency. [Preview Abstract] |
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H1.00097: Influence of Graphite Size on the Synthesis and Reduction of Graphite Oxides Hae Kyung Jeong We investigated the influence of the precursor, graphite, size on the synthesis and reduction of graphite oxide. Three precursors of graphite with different size were used to synthesize the graphite oxide which was consecutively reduced by hydrazine of different concentration ratios. Size dependent effect on the reduction of the graphite oxide was found, and the graphite oxide of the smallest size provided the best reduction result. Electrochemical properties of the reduced graphene oxide were investigated in both of the base and acid electrolytes, finding the reduced graphene oxide of the smallest size gives the best electrochemical performance due to the high reduction. Therefore, the precursor size is a very important factor in the synthesis and reduction of graphite oxide, affecting the electrochemical performance considerably for the energy storage applications. [Preview Abstract] |
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H1.00098: Effect of electron acceptor structure on stability and efficiency in polymer photovoltaics: a library approach Michael Tro, David Oparko, Emma Lewis, Alexis Sarabia, Maxwell Giammona, Justin Isaac, Thorsteinn Adalsteinsson, Brian McNelis, Richard Barber A commonly studied polymer photovoltaic system is prepared using a mixture of poly[3-hexylthiophene] (P3HT) as the electron donor and [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) as the electron acceptor. We have prepared a series of PCBM analogs, making a variety of fullerene esters using commercially available primary alcohols. The first studies involved attaching an eight- or eighteen-carbon chain in place of the single carbon in PCBM. Solar cells made from these compounds exhibited improved lifetimes, motivating further exploration in the domain of possible attachments. We have now created a small library of these acceptor compounds and blended them with P3HT to prepare and measure solar cells. We collect current-voltage data over hours or days for each sample under ambient air conditions. These data provide not only the standard figures of merit, but also reveal the time dependence of these values. We have already observed significant differences between fullerene esters that are very similar in structure. [Preview Abstract] |
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H1.00099: The peak effect of the photocurrent from thylakoids on the concentration of electron mediators Yue Yu, Fulin Zuo, Chen-Zhong Li Photocurrent extracted from the thylakoids has been studied as a function of electron mediator concentration. The electron mediators are used to facilitate the charge transfer from the thylakoid's charge transport chain to the outside medium. This measured photocurrent has been checked to originate from the photosynthesis on the thylakoid membranes. The photocurrent has a linear dependence on light intensity. It shares similar frequency dependence as that of absorption spectrum of chlorophyll and it decreases or disappears with the application of an inhibitor. We report here a new peak effect in the photocurrent as a function of the concentration of electron mediators. A simplistic model is proposed to explain the peak effect. [Preview Abstract] |
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H1.00100: Absorption spectra and photoresponse observation of Cu$_{2}$O thin film photoanodes Endri Mani, Rohana Garuthara Electrodeposition was used to deposit Cu$_{2}$O thin films on ITO substrates. The deposited Cu$_{2}$O films were characterized by photocurrent, absorption and reflectance spectroscopy. Photoresponse of the film clearly indicated n-type behavior of Cu$_{2}$O in photoelectrochemical cells. The effects of chlorine doped photoanodes deposited in different solution pH on the magnitude of their photocurrent are studied. The low temperature absorption spectra of chlorine doped Cu$_{2}$O films are found to depend on the solution pH in the range 10.0-7.5. Optical absorption spectra of Cu$_{2}$O films were measured in the temperature range 79K - 295K. The Urbach's tail was observed for n-type conductive Cu$_{2}$O films in the temperature range 79K to 295K. The Urbach's energy as a function of temperature for Cu$_{2}$O films were studied. The results will be discussed with emphasis on the reflectance, absorption and photoresponse observation. [Preview Abstract] |
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H1.00101: Synthesis and Characterization of ZnO/polymer planar heterojunction solar cells Leandro Gutierrez, William Manners, Arya Nabizadeh, Patrick Albers, Jesus Duran, Anthony Scudieri, Anne Isah, Michael McDougall, Mehmet Sahiner, Weining Wang ZnO/polymer heterojunction has been studied by many groups for its potential application in solar cell, LED, UV photodetection and other applications. However, there are few studies on ZnO/polymer heterojunction by synthesizing ZnO using pulsed laser deposition (PLD). Comparing with other methods, PLD has the advantage of congruent evaporation, and being able to grow high quality thin films at relatively low temperature. In our previous work in pulsed-laser-deposited (PLD) ZnO/PEDOT:PSS heterojunction, correlations between the annealing conditions of pulsed laser deposition and the electrical performance of solar cells have been observed. In this work, we report two new studies: 1) Studies on how the performance of the PLD-ZnO /PEDOT:PSS heterojunction depends on polymer conductivity; 2) Comparison studies on PLD-ZnO/PEDOT:PSS and PLD-ZnO/P3HT heterojunction. We studied how the performance of ZnO/polymer solar cells depend on the polymer work function and conductivities and deposition condition of ZnO. X-ray diffraction (XRD) and scanning electron microscopy were used to characterize the PLD-ZnO film. The correlation between the solar cell electrical performance and the polymer conductivity and pulsed laser deposition conditions will be discussed. [Preview Abstract] |
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H1.00102: Looking for Small Changes in Heat Capacity using Differential Scanning Calorimeter Will Linthicum, Andrew Laugharn, Samuel Amanuel One of the major drawbacks of renewable energy is the lack of adequate and economical means of storage. In the case of concentrated solar power a large amount of thermal fluid is required to store a reasonable amount of energy to meet demands. This is primarily because the fluids tend to have a low specific heat capacity. Formulating composites of these fluids can enhance their specific heat capacity and avails opportunities to make concentrated solar power more attractive. Traditionally, the specific heat capacity of composite materials is computed from the weighted average of the individual heat capacities. This, however, does not take into account interfacial effects where the heat capacity could be different. Although, these changes in heat capacity may be small in traditional composites, they could be significant in the case of nanocomposites. From our phase transition studies of fluids confined in nano pores, we have demonstrated that the molecules at the interface have different thermodynamic behavior. In this presentation, we show our systematic studies and development of a baseline useful in evaluating small changes in heat capacity using a power compensated differential scanning calorimeter [Preview Abstract] |
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H1.00103: Relationship Between Absorber Layer Properties and Device Operation Modes For High Efficiency Thin Film Solar Cells Ram Ravichandran, Robert Kokenyesi, John Wager, Douglas Keszler A thin film solar cell (TFSC) can be differentiated into two distinct operation modes based on the transport mechanism. Current TFSCs predominantly exploit diffusion to extract photogenerated minority carriers. For efficient extraction, the absorber layer requires high carrier mobilities and long minority carrier lifetimes. Materials exhibiting a strong optical absorption onset near the fundamental band gap allows reduction of the absorber layer thickness to significantly less than 1 $\mu$m. In such a TFSC, a strong intrinsic electric field drives minority carrier extraction, resulting in drift-based transport. The basic device configuration utilized in this simulation study is a heterojunction TFSC with a p-type absorber layer. The diffusion/drift device operation modes are simulated by varying the thickness and carrier concentration of the absorber layer, and device performance between the two modes is compared. In addition, the relationship between device operation mode and transport properties, including carrier mobility and minority carrier lifetime are explored. Finally, candidate absorber materials that enable the advantages of a drift-based TFSC developed within the Center for Inverse Design are presented. [Preview Abstract] |
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H1.00104: The Effects of Extreme Cold on Polycrystalline Photovoltaic Solar Cells Robert Stiffler, Billy Cimorelli, Seth Fasig, Evan Hirschmugl, Paul Quinn This project will examine how solar cells perform under conditions of extreme cold. Polycrystalline photovoltaic solar cells were tested to get their baseline currents and voltages, producing the standard IV curve. The cells were then submerged in liquid nitrogen for set intervals of time. Once removed from the nitrogen, they were allowed to reach room temperature and sit overnight. Each cell was then retested to get new currents and voltages, producing a new IV curve. The experiments produced results showing that the submersion in liquid nitrogen actually improved their performance. This implies that under certain conditions, exposure to extreme cold could actually enhance the performance of polycrystalline photovoltaic solar cells. [Preview Abstract] |
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H1.00105: Higher Efficiency for Quasi-Solid State Dye Sensitized Solar Cells Under Low Light Irradiance Ajith DeSilva, T.M.W.J. Bandara, H.D.N.S. Fernado, P.S.L. Fernando, M.A.K.L. Dissanayake, W.J.M.J.S.R. Jayasundara, M. Furlani, B.-E. Mellander Dye-sensitized solar cells (DSSCs), lower cost solar energy conversion devices are alternative green energy source. The liquid based electrolyte DSSCs have higher efficiencies with many practical issues while the quasi-solid-state DSSCs resolve the key problems but efficiencies are relatively low. Polyacrylonitrile (PAN) based gel polymer electrolytes were fabricated as DSSCs by incorporating ethylene carbonate and propylene carbonate plasticizers and tetrapropylammonium iodide salt. A thin layer of electrolyte was sandwiched between the TiO2 anode (sensitized with N719 dye) and the Pt counter electrode. The electrolyte had an ionic conductivity of 2.6 mS/cm at 25 degrees of Celsius. DSSCs incorporating this gel electrolyte revealed Vsc circuit, Jsc, fill factor (FF) and efficiency values of 0.71 V, 11.8 mA, 51 percent and 4.2 percent respectively under 1 sun irradiation. The efficiency of the cell increased with decreasing solar irradiance achieving up to 10 percent efficiency and 80 percent FF at low irradiance values. This work uncovers that quasi-solid state DSSCs can reach efficiencies close to that of liquid electrolytes based cells. [Preview Abstract] |
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H1.00106: Water photolysis by the K$_{2}$Ln$_{2/3}$Ta$_{2}$O$_{7}$ and K$_{2}$LnTa$_{3}$O$_{10}$ (Ln$=$La, Pr, Nd) tantalates Hoover Valencia-Sanchez, Alicia Negron-Mendoza, Dwight Acosta-Najarro, Pablo de la Mora, Gustavo Tavizon Six compounds of the hydrated phase of K$_{2}$Ln$_{2/3}$Ta$_{2}$O$_{7}$ and K$_{2}$LnTa$_{3}$O$_{10}$ were prepared by the polymerizable complex method; these compounds were characterized in crystal structure, specific surface area (BET), optical band gap (DRS) and reactivity for water photolysis using a 300 W Hg-lamp. Tantalates containing La, Pr and Nd show a shift in the band gap value, from 3.8, 2.6 and 2.07 eV, respectively. Hydrogen production without co-catalyst has been observed, and no noticeable difference appears when NiO$_{x}$ was impregnated to powders. The hydrogen production notably increases when a sacrificial agent as methanol was used. In this work we compare the hydrogen production efficiencies for the bi-octahedral and three-octahedral tantalum hydrated compounds. [Preview Abstract] |
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H1.00107: Formula of an ideal carbon nanomaterial supercapacitor Larissa Samuilova, Alexander Frenkel, Vladimir Samuilov Supercapacitors exhibit great potential as high-performance energy sources for a large variety of potential applications, ranging from consumer electronics through wearable optoelectronics to hybrid electric vehicles. We focuse on carbon nanomaterials, especially carbon nanotube films, 3-D graphene, graphene oxide due to their high specific surface area, excellent electrical and mechanical properties. We have developed a simple approach to lower the equivalent series resistance by fabricating electrodes of arbitrary thickness using carbon nanotube films and reduced graphene oxide based composites. Besides of the problem of increasing of the capacitance, the minimization of the loss tangent (dissipation factor) is marginal for the future development of the supercapacitors. This means, not only a very well developed surface area of the electrodes, but the role of the good quality of the porous separator and the electrolyte are important. We address these factors as well. [Preview Abstract] |
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H1.00108: APPLICATIONS |
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H1.00109: Spin-motive Force Induced by Domain Wall Dynamics in the Antiferromagnetic Spin Valve Ryoko Sugano, Masahiko Ichimura, Saburo Takahashi, Sadamichi Maekawa In spite of no net magnetization in antiferromagnetic (AF) textures, the local magnetic properties (Neel magnetization) can be manipulated in a similar fashion to ferromagnetic (F) ones [1,2]. It is expected that, even in AF metals, spin transfer torques (STTs) lead to the domain wall (DW) motion and that the DW motion induces spin-motive force (SMF). In order to study the Neel magnetization dynamics and the resultant SMF, we treat the nano-structured F1/AF/F2 junction. The F1 and F2 leads behave as a spin current injector and a detector, respectively. Each F lead is fixed in the different magnetization direction. Torsions (DW in AF) are introduced reflecting the fixed magnetization of two F leads. We simulated the STT-induced Neel magnetization dynamics with the injecting current from F1 to F2 and evaluate induced SMF. Based on the adiabatic electron dynamics in the AF texture [2], Langevin simulations are performed at finite temperature.\\[4pt] [1] F. Y. Yang and C. L. Chien, Phys. Rev. Lett. 85, 2597 (2000); J. M. Logan et al., Appl. Phys. Lett. 100, 192405 (2012).\\[0pt] [2] R. Cheng and Q. Niu Phys. Rev. B 86, 245118 (2012); A. C. Swaving and R. A. Duine, Phys. Rev. B 83, 054428 (2011); E. G. Tvetenet al.,Phys. Rev. Lett. 110,127208 (2013). [Preview Abstract] |
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H1.00110: Nanoscale rectenna for broadband rectification of light from infrared to visible Darin Zimmerman, James Chen, Michael Phillips, Dennis Rager, Zachary Sinisi, Raymond Wambold, Gary Weisel, Brock Weiss, Brian Willis, Nicholas Miskovsky We describe a novel approach to the efficient collection and rectification of solar radiation in a device designed to operate from the infrared through the visible. Here, a nanoscale, rectenna array acts both as an absorber of incident radiation and as a rectifier. Rectification derives not from temperature or material asymmetry, as with metal-insulator-metal or silicon-based, Schottky diodes. Instead, it derives from the geometric asymmetry of the rectenna, which is composed of a pointed tip and a flat collector anode. In this arrangement, the difference between the potential barriers for forward and reverse bias results in a rectified dc current. To achieve anode-cathode gap distances within the tunneling regime, we employ selective atomic-layer deposition of copper applied to palladium rectenna arrays produced by electron-beam lithography. We present details of device fabrication and preliminary results of computer simulation, optical characterization, and electro-optical response. [Preview Abstract] |
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H1.00111: Conversion of concentrated solar radiation by quantum dots with built-in charge Nizami Vagidov, Andrei Sergeev, Vladimir Mitin, Kimberly Sablon, Serge Oktyabrsky, Michael Yakimov Quantum dots with built-in charge provide broadband conversion, which includes IR range of solar radiation. The multistep IR harvesting in quantum dots (QD) is strongly enhanced by the n-doping of the interdot space. The doping also suppresses electron capture processes and reduces recombination losses. We designed, fabricated, tested, and optimized the solar cell devices with charged QDs. Basic parameters of the devices (short circuit current, open circuit voltage, and conversion efficiency) are investigated in the range of 1 -- 100 Suns. It has been experimentally demonstrated that the conversion of IR radiation increases with concentration. The effect is associated with extraction of electrons from charged QDs due to interaction with hot electrons. [Preview Abstract] |
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H1.00112: Multi-elemental INAA and CF-LIBS techniques for analysis of rocks of Ethiopian Tropical forest area of Tepi Dilbetigle Mamo, Chaubey Ashok Extensive use of minerals in the world entails the evaluation of major, minor and trace element contents in rocks of different areas. Instrumental neutron activation analysis and calibration free laser induced breakdown spectroscopy were successfully employed to identify and determine the concentration of elements in the rock samples which are collected from the untouched tropical forest area of Ethiopia. Using both techniques 26 minerals are identified and the concentration of each element was estimated and compared to one another. Due to the weak neutron source and the technique limitation, only eight elements of the rock samples were identified by neutron activation analysis. This study provides the baseline value of certain essential minerals in the rocks of studied area and the result shows that the studied area has great potential for mining of Pt and Zn elements. The performances of two analytical methods have been compared. Concentration analysis was done using a Calibration Free-laser induced breakdown spectroscopy algorithm in MATLAB environment. [Preview Abstract] |
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H1.00113: Optomechanical waveguide system for switching telecom light Tomohiro Tetsumoto, Takasumi Tanabe We numerically study an optomechanical directional coupler switch based on silica zipper cavity. Unlike silicon, silica is transparent in both visible and telecom wavelength, which allows the device to operate with ultra-broad wavelength. The zipper cavity is composed of pair of one dimensional photonic crystal ladder, which we use as an opto-mechanical tunable active directional coupler. We modulated the lattice constant of the Bragg mirror to enable mode-gap confinement at visible range ($Q\approx 2\times 10^{4})$. The signal is telecom light, of which wavelength is below the modegap and can propagate the waveguide without exhibiting mode-gap confinement. At initial state, signal light can evanescently couple from one ladder to another, which allows the device to behave as a directional coupler. We next change the gap between waveguides by means of optical force induced by visible pump light. This changes the coupling rate and switches the propagation direction of the light. The induced force is calculated as 0.1 $\mu $N/pJ. This shows that the gap will broaden over 100 nm with 50 pJ pumping energy. This displacement will change the coupling rate between two waveguides and allows waveguide switching. We showed the switching of visible light with telecom light, and demonstrated numerically that the extinction ratio for this switch is over 15dB. [Preview Abstract] |
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H1.00114: Design and implementation of a photonic device with large tunable group delay Kwok Lo, Tao Zhou We have designed and fabricated an optical fiber based photonic device exhibiting very large tunable group delay, with delay time in the order of microsecond, by taking advantage of polarization related group delay in multiple section of PM fibers. More importantly, this large group delay can be tuned swiftly through external control. Such a device is potentially very helpful for all optical switching/routing and microwave photonic controlling, in which large tunable group delay is needed. [Preview Abstract] |
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H1.00115: Extreme ultraviolet Fourier holography of nano-scale objects Mario Marconi, Nils Monserud, Erik Malm, Przemyslaw Wachulak, Xu Huiwen, Ganesh Balakrishnan, Weilun Chao, Erik Anderson Fourier transform holography (FTH) is one of the leading short wavelength coherent diffraction imaging techniques. FTH requires precise mask (object) fabrication procedure, but the object reconstruction process is fast and simple. FTH is a coherent imaging technique which utilizes the interference between a point source reference and the object waves to encode object information into the interference pattern. The image of the object can be numerically reconstructed by applying the inverse Fourier transform of the interference pattern. This simple reconstruction method allows for using charge coupled device (CCD) detectors for the recording medium. To obtain high spatial resolution it is necessary to utilize small pinholes in the reference that limits the area of the object to small sizes to match the amount of light from the object to the intensity of the reference pinhole. Therefore, high-resolution mask-based FTH ultimately limits the object size that can be imaged. In this paper, we present a setup that uses a Fresnel zone plate to split the coherent beam of a compact extreme ultraviolet (EUV) laser that allows large field of view, high spatial resolution, time resolved EUV holograms in a table top. [Preview Abstract] |
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H1.00116: Improvement in resistive switching properties of NiO thin films using ion beam treatment Yeon Soo Kim, Sung Moon Hwang, Jihoon Jeon, Yoon Seung Nam, Sangik Lee, Chan Soo Yoon, Taekjib Choi, Bae Ho Park Resistive switching phenomena have attracted much interest due to its potential application for next generation non-volatile memory. Although many researches have been conducted for real application, their some drawbacks, such as poor operation voltage distribution, are remained as critical obstacles. To solve the problems by finding their switching phenomena the filament formation/rupture hypothesis is widely used, however, microscopic mechanisms are still veiled. We deposited NiO thin films with reactive dc magnetron sputter on Pt/Ti/SiO$_{2}$/Si substrates at 500 $^{\circ}$C. Various sized patterns were fabricated by using photolithography, and then Pt electrodes were deposited. These structures show typical unipolar resistive switching behaviors. Before depositing top electrodes, we have treated NiO surface by using Ar$^{+}$ ion beams with various conditions. Although Ar$^{+}$ ion bombardment did not cause obvious thickness change of the film, fundamental properties of the Pr/NiO/Pt capacitor such as breakdown voltage have been drastically changed. We believe that variations of nickel-oxygen bonding in the vicinity of NiO surface played important roles in such changes and thus optimized Ar$^{+}$ ion bombardment condition would improve resistive switching properties. [Preview Abstract] |
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H1.00117: Quantum-accurate AC voltage synthesis at NIST: Results and Applications Jason Underwood, Alain Rufenacht, Paul Dresselhaus, Charles Burroughs, Sam Benz Recent advancements in manufacturing, communications, and electrical power distribution demand increasingly precise electrical measurements of arbitrary waveforms. Representative examples are power factor measurements of 50/60 Hz pure sinusoids for the smart grid industry and spectral purity analysis of RADAR subsystems. To help meet this demand, NIST has developed an intrinsic (quantum-referenced) AC Josephson voltage standard (ACJVS). The ACJVS is capable of synthesizing pure tones with quantum accuracy and with unprecedented low in-band harmonic content. The ACJVS functions as a quantum digital-to-analog converter: driving the system with a high-speed digital pulse train yields perfectly quantized voltage pulses, whose time-integrated areas are exactly $h$/2$e$. We report a doubling of output rms voltage by successfully operating on the $n=$ 2 Shapiro step, in which every Josephson junction produces two quantized pulses for every input pulse,. We also discuss progress toward automating the operation of the ACJVS, with the goal of expanding accessibility to a broader community of users. Finally, we discuss future goals to increase rms output to beyond 1 V, expand bandwidth to 1 MHz, and the development of a bandpass topology for RF output up to 100 MHz. [Preview Abstract] |
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H1.00118: Treatment for Traumatic Brain Injury in Mice Using Transcranial Magnetic Stimulation: A Preliminary Study Alexandria Carr, Gary Zenitsky, Lawrence Crowther, Ravi Hadimani, Vellareddy Anantharam, Anumantha Kanthasamy, David Jiles Transcranial magnetic stimulation (TMS) is a non-invasive surgery-free tool used to stimulate the brain by time-varying magnetic fields. TMS is currently being investigated as a treatment for neurological disorders such as depression, Parkinson's disease and TBI. Before moving to human TMS/TBI trials, animal testing should be pursued to determine suitability and adverse effects. As an initial study, four healthy mice were treated with TMS at different power levels to determine short-term behavioral effects and set a control group baseline. The mouse's behavior was studied using the Rotorod test, which measures the animal's latency to fall off a rotating rod, and the Versamax test, which measures horizontal and vertical movement, and total distance traveled. The Rotorod test has shown for TMS power levels $\ge $90{\%} the mice begin to fall directly post-treatment. Similarly, the Versamax test has shown for power levels $\ge $80{\%} the mice are less mobile directly post-treatment. Versamax mobility was found to return to normal the day following treatment. These mice were housed in the facility for 4 months and the behavioral tests were repeated. Versamax results showed there was no significant variation in mobility indicating there are no long-term side effects of TMS treatment on the mice. [Preview Abstract] |
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H1.00119: ABSTRACT WITHDRAWN |
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H1.00120: Development of functionalized nanodiamond fluorescence detection platform: Analysis the specific promoter regulated by p53 Diansyue Wu, Hsueh-Liang Chu, Hung Chuang, Yu-Ning Lu, Li-Ping Ho, Hsing-Yuan Li, Ming-Hua Hsu, Chia-Ching Chang Nanodiamond (ND) is one of the biocompatible nanomaterials with large tunable surface for chemical modification. It possesses unique mechanical, spectroscopy, and thermal properties. It is an excellent molecular vehicle to deliver specific molecules in biological system. The green fluorescent protein (GFP) is a protein that emits strong green fluorescence when it is excited by ultra-violet to blue light. It makes GFP a good indicator. By combining ND-GFP, a visible biocompatible delivery system will be developed. p53 is a tumor suppressor protein encoded by the TP53 gene. P53 plays an important role in apoptosis, genomic stability, and inhibition of angiogenesis by interacting with specific DNA sequence of promoter of related genes. In this study, a p53 functionalized ND-GFP will be developed. This complex can recognize the specific DNA sequence of promoter and the intermolecular interactions can be monitored directly by fluorescence and Raman spectroscopy both in vivo and in vitro. [Preview Abstract] |
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H1.00121: New Applications of Portable Raman Spectroscopy in Agri-Bio-Photonics Dmitri Voronine, Rob Scully, Virgil Sanders Modern optical techniques based on Raman spectroscopy are being used to monitor and analyze the health of cattle, crops and their natural environment. These optical tools are now available to perform fast, noninvasive analysis of live animals and plants \textit{in situ}. We will report new applications of a portable handheld Raman spectroscopy to identification and taxonomy of plants. In addition, detection of organic food residues will be demonstrated. Advantages and limitations of current portable instruments will be discussed with suggestions for improved performance by applying enhanced Raman spectroscopic schemes. [Preview Abstract] |
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H1.00122: Experimental Study of the Temperature Dependence of Substrate Coverage in Ionic Self-Assembled Monolayers Brian Simpson, Mohammad Abudayyeh, Md Ali, Alena Hamrick, Dan Mazilu, Irina Mazilu We investigate the temperature dependence of the surface coverage of thin films consisting of silica nanoparticles deposited on glass substrates via the ISAM (ionically self-assembled monolayers) technique. Variables such as the concentration and pH of the silica colloidal suspension and polyelectrolyte solution, dipping time, and particle size among others are controlled, and the thin films are deposited on substrates under a range of temperature values. The samples are analyzed using scanning electron microscopy. The surface coverage is estimated by employing a pixel-count comparison of grayscale values in the SEM micrographs and~compared to analytical results obtained using a cooperative sequential adsorption model. [Preview Abstract] |
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H1.00123: Electron Tunneling in Quantum Rings in an Electric Field Oluwafemi Adelegan, Igor Filikhin, Branislav Vlahovic, James Nimmo, Igor Martinyan Double concentric quantum rings (DCQRs) composed of InGaAs in a GaAs substrate utilizing a \textbf{\textit{kp}}-perturbation single sub-band approach with the effective potential approach were theoretically studied. Two dimensional (2D) objects were considered. Statistical analysis of these DCQRs in the absence of an applied electric field was compared with these DCQRs when a static electric field was applied to them. The statistical analysis consists of taking the difference of the probability of finding an electron in the inner ring and outer ring, dividing by the sum of these probabilities. [Preview Abstract] |
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H1.00124: SUPERLATTICES, NANOSTRUCTURES AND OTHER ARTIFICIALLY STRUCTURED MATERIALS |
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H1.00125: Experimental and Theoretical Studies of Photonic Band gaps in Artificial Opals Lei Wang, Ming Yin, Fouzi Arammash, Timir Datta Photonic band structure and band gap were numerically computed for a number of closed packed simple cubic and Hexagonal arrangements of non-conducting spheres using ``Finite Difference Time Domain Method''. Photonic gaps were found to exist in the simple cubic overlapping spheres with index of refraction (n) \textgreater 3.2. Gap increased linearly from 0.117- 0.161 (1/micron) as lattice constant decreased from 0.34 to 0.18 (micron). For less than 3.2 no gap was obtained. Also, no gaps were obtained for hexagonal packing. UV-VIS reflectivity and transmission measurements of polycrystalline bulk artificial opals of silica (SiO2) spheres, ranging from 250nm to 300nm in sphere diameter indicate a reflection peak in the 500-600 nm regimes. Consistent with photonic band gap behavior we find that reflectivity is enhanced in the same wavelength where transmission is reduced. To the best of our knowledge this is the first observation of photonic gap in the visible wave length under ambient conditions. The wave length at the reflectance peak increases with the diameter of the SiO2 spheres, and is approximately twice the diameter following Bragg reflection. [Preview Abstract] |
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H1.00126: Vacancy Interlayer Migration in Multi-layered Graphene Lili Liu, Junfeng Gao, Xiuyun Zhang, Tianying Yan, Feng Ding Graphene has innumerous applications due to its exceptional properties. Various defects that may be introduced into the graphene lattice during synthesis and/or post-treatments are known have significantly impact on these properties. So engineering graphene by introducing or annealing of defects is an important technology to achieve desired properties for various applications. Therefore a comprehensive understanding on the behavior of defects in graphene is critically important. Here, interlayer migration of the vacancies in multi-layered graphene (MLG) was investigated by density functional tight-binding molecular dynamic simulations and first principle calculations. Our study reveals that, although the direct vacancy migration between neighboring graphene layers (NGLs) is prohibited by a very high barrier up to $\sim$ 7 eV, the interaction between vacancies or vacancy and holes in NGLs can greatly reduce the barrier to $\sim$ 3 eV and expedites the migration process. Our study reveals a new mechanism of the defect self-healing in MLG and multi-walled carbon nanotubes and it can be used to engineer desired graphene materials. [Preview Abstract] |
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H1.00127: Operations of Majorana Bound States in Charge-qubit Arrays Ting Mao, Zidan Wang The experimental pursuit of Majorana bound state (MBS) in one-dimensional (1D) solid state systems has been brought into the limelight since the proposal of Kitaev's toy lattice model. Here we use the inductively coupled charge-qubit array to realize a tunable Kitaev model. With the advantages of the superconducting-qubit circuit, we can manipulate the parameters of Kitaev model and change the symmetry class to which the model Hamiltonian belongs from the class D to the class BDI. We also discuss a simple class DIII model constructed by coupling two copies of the class D charge-qubit array. Using the time reversal symmetry and a residual $U(1)$ spin rotation symmetry of the model, we explore the possibility of implementing universal single topological qubit operations. [Preview Abstract] |
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H1.00128: Selfassembled Metamaterials: Minkowski Spacetime Analogue Bradley Yost, David Lahneman, Evan Bates, Vera Smolyaninova, Igor Smolyaninov Hyperbolic metamaterials are artificially created materials with optical properties that are drastically different along different axes. Due to the hyperbolic dispersion relation, light rays propagating inside a hyperbolic metamaterial look similar to particle world lines in a 2$+$1 dimensional Minkowski spacetime. In our study we used a ferrofluid, which is much easier to fabricate than typical metamaterials. A ferrofluid contains a known concentration of ferromagnetic nanoparticles in a carrier fluid. In the absence of an external magnetic field, the particles are in random order. When an external magnetic field is applied, the particles form nanocolumns, which align in the direction of the applied magnetic field, resulting in geometry similar to a metal nanowire array seen in hyperbolic metamaterials. These nanocolumns align along the magnetic field, so that a hyperbolic metamaterial may be formed at sufficient concentrations, n$_{\mathrm{H}}$. We have studied polarization-dependent optical transmission of the cobalt based ferrofluid just below n$_{\mathrm{H}}$. Due to thermal fluctuations of the concentration of cobalt nanoparticles in the ferrofluid, hyperbolic regions spontaneously appear. Light rays inside these regions look similar to particle world lines in a 2$+$1 dimensional Minkowski spacetime. These regions in the ferrofluid are analogous to transient ``Minkowski spacetimes'' or individual Minkowski universes, which appear and disappear. [Preview Abstract] |
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H1.00129: Large vacuum Rabi splitting for a semiconductor nanogap cavity Mitsuharu Uemoto, Hiroshi Ajiki A metallic nanogap utilizing surface plasmon excitation is one of the most popular designs of an optical antenna converting propagating radiation into enhanced fields at a nanoscale area (hotspot). Similarly, a nanogap structure consisting of a semiconductor dimer also causes the hotspot due to exciton. This semiconductor nanogap acts as a high-Q microcavity because of the small losses of the exciton resonance, for example, the Q factor of the nanogap structure whose long axis is smaller than $32$ nm becomes $\approx 10^4$ [1]. This fact is quite contrast to the low-Q factor $\approx 10$ of a metallic nanogap . In this work, we theoretically demonstrate the vacuum Rabi splitting of a two-level system placed at the semiconductor nanogap cavity. The resulting splitting energy reaches $\approx 0.5$ meV for dipole moment $10$ D of the two-level system, which is much larger than the splitting energy of matter with the same dipole moment embedded in a photonic-slab cavity [2].\\[4pt] [1] M. Uemoto and H. Ajiki, in preparation.\\[0pt] [2] T. Yoshie et al., ``Vacuum Rabi splitting with a single quantum dot in a photonic crystal nanocavity,'' Nature, vol. 432, pp. 9-12, 2004. [Preview Abstract] |
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H1.00130: Broadband Terahertz Generation from Metamaterials Liang Luo, Ioannis Chatzakis, Jigang Wang, Fabian Niesler, Martin Wegener, Thomas Koschny, Costas Soukoulis The Terahertz spectral regime ranging from about 0.1 to 15 THz is one of the least explored yet most technologically transformative spectral regions. One key current challenge is to develop efficient and compact THz emitters/detectors with a broadband and gapless spectrum that can be tailored for various pump photon energies. Recently, the development of metamaterials composed of split ring resonators (SRRs) has enabled researchers to tailor resonant optical nonlinearities from THz to infrared and visible regions. Here we demonstrate efficient single-cycle, broadband THz generation, ranging from about 0.1 to 4 THz, from a thin layer of SRRs with tens of nanometers thickness by pumping at 1.5 $\mu $m wavelength of the ultrafast laser pulses. The THz emission arises from exciting the magnetic-dipole resonance of SRRs. This, together with pump polarization dependence and power scaling of the THz emission, identifies the role of optically induced nonlinear currents in SRRs. We reveal a giant sheet nonlinear susceptibility in the order of 10$^{-16}$ m$^{2}$/V that far exceeds thin films and bulk non-centrosymmetric materials such as ZnTe. [Preview Abstract] |
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H1.00131: Blinking in Small Clusters of Semiconductor Nanocrystals Kevin Whitcomb The fluorescence blinking of individual semiconductor nanocrystals (NCs) is also observed in small systems of NCs. Clusters containing fewer than a dozen interacting NCs exhibit an enhanced blinking due to interactions within the cluster. The dynamics of this blinking support a model in which energy transfer to a single NC within the cluster dominates the fluorescence of the entire cluster. [Preview Abstract] |
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H1.00132: Visualization study of the normal-fluid motion in superfluid helium-4 Jian Gao, Alex Marokov, Wei Guo, Steven W. Van Sciver, Gary G. Ihas, Daniel N. McKinsey, William F. Vinen Flow visualization in superfluid $^{\mathrm{4}}$He is challenging, yet crucial for attaining a detailed understandingof quantum turbulence. Two problems have impeded progress: finding and introducing suitable tracersthat are small yet visible; and unambiguous interpretation of the tracer motion. Metastable He$_{\mathrm{2}}$ triplet molecules form angstrom-sized bubbles in helium and can be imaged using a laser-induced-fluorescence technique. At temperatures above 1 K, helium molecules solely follow the motion of the normal-fluid component without being affected by quantized vortices. In our recent experiments on thermal counterflow, by tracing a thin molecular line created via femtosecond-laser field-ionization technique, we are able to measure the instantaneous normal-fluid velocity field. We show that the obtained velocity probability density function (PDF) obeys a Gaussian distribution. We also discuss the calculated structure function of the novel normal-fluid turbulence in thermal counterflow. [Preview Abstract] |
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H1.00133: Spatially-Resolved Upconversion Luminescence in NaYF$_4$:Yb:Er Nanoparticles on Au Nano-Cavity Arrays Jon Fisher, Amy Hor, Steve Smith, Bo Zhao, Quocahn Luu, P. Stanley May Spectroscopic imaging was used to study the surface plasmon polariton (SPP) enhanced upconversion luminescence of NaYF$_4$:Yb:Er nanoparticles embedded in PMMA, supported on Au Nano-cavity arrays created by electrodeposition and nanosphere lithography. Spatially-resolved upconversion spectra of these samples show a maximal power-dependent enhancement of approximately 3X over similar layers on adjacent smooth Au surfaces under high excitation intensity, and relatively weaker enhancements at lower excitation intensity. Comparisons to wide-field images of the Nano-cavities show enhancement clearly associated with the formation of the nano-cavity arrays. The width and relative position of the statistical distributions of intensities in the spectroscopic images on and off the nano-cavity arrays were analyzed and found to be strongly dependent on the excitation intensity. The presence of the SPP was confirmed by spectrally resolved reflectivity, and the mechanism for luminescence enhancement was investigated by time resolved measurements of the luminescence decay. Reflectivity measurements are compared to finite difference time domain simulations (FDTD). [Preview Abstract] |
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H1.00134: SERS Plasmonic Enhancement using DNA Origami-based Complex Metallic Nanostructures Anne Watson, Mauricio Pilo-Pais, Steven Demers, Thom LaBean, Gleb Finkelstein We construct Surface-Enhanced Raman Scattering (SERS) substrates using ``DNA origami'' templates. Using DNA complementarity, we selectively attach 5 nm gold nanoparticles at the corners of rectangular origami ($\sim$100 nm in size). We then controllably enlarge them using in-solution silver deposition to create nanometer-sized gaps between the particles. The small gaps are responsible for the strong enhancement of the electromagnetic field (``hot spots''). We covalently attached Raman molecules (4-aminobenzenethiol) to the nanoparticles, and measured the Raman signal enhancement in the hot spots to be a factor of $\sim$100, compared to single nanoparticle samples which lack inter-particle hot spots. We anticipate extending this technique by selectively placing molecules directly within the hot spots for single-molecule biosensor applications. Our method illustrates the functionality and versatility of utilizing DNA origami to rationally design and assemble plasmonic structures for molecular spectroscopy. [Preview Abstract] |
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H1.00135: Charge sensing by altering the phase transition in VO2 Suhas Kumar, Rahim Esfandyarpour, Ronald Davis, Yoshio Nishi We use vanadium dioxide to sense changes in surface charge accumulation and explore possibilities of sensing presence of large polar molecules. It was shown last year [1] that surface charge accumulation can cause bulk delocalization. It was also shown that surface charge accumulation can cause a decrease in the insulator-metal transition temperature of vanadium dioxide. We use this concept and replace the surface charges with molecules that have a net polarization. We used biotinylated bovine serum albumin (BBSA) and streptavidin in our experiments. We observed a change in the potential and current at which the switching of resistance happened. This implied a change in the power and hence the temperature at which the Mott transition happened. When these molecules are held on the surface of VO2, we postulate that they transfer charges, which is what we are sensing as changes in the temperature at which a phase transition happens. We believe this shows the possibility of sensing a variety of molecules that are of interest to biologists, chemists and environmentalists. [1] Nakano et. al., Nature 487, 459 (2012) [Preview Abstract] |
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H1.00136: Evidence of two-dimensional quantum Wigner Crystal in a zero magnetic field Jian Huang, Loren Pfeiffer, Ken West In disorder-dominated cases, Anderson localization occurs as a result of destructive interference effects caused by (short-ranged) random disorders. On the other hand, in interaction-dominated scenarios, striking manifestations of quantum physics emerge in response to strong inter-particle Coulomb energy ($E_C$). The most prominent interaction-driven effect is the Wigner crystallization (WC) of electrons, an electron solid made up with spatially separated charges settling in a form of a lattice. The classical version of the crystallization, with the Debye temperature $\Theta_D < E_C$, has been demonstrated with two-dimensional (2D) electrons on helium surfaces (EHS). However, the more desired quantum version with the Fermi energy $E_F\ll E_C\ll \Theta_D$, has not been previously observed especially in zero magnetic field. We present a transport study of ultra-high quality dilute two-dimensional hole (2DH) systems in a genuine interaction-driven regime. A high resolution dc VI measurement reveals a $p$A level threshold transport accompanied by resistivity oscillations, indicating the coexistence of a pinned quantum WC with discrete edge filaments of unpinned carriers. [Preview Abstract] |
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H1.00137: Monte Carlo Simulations of Focused Electron Beam Induced Etching Rajendra Timilsina, Philip Rack, Karsten Wolff, Michael Budach, Klaus Edinger Focused beam (electron-ion-photon) induced processing has long been utilized as a micro-/nano-scale direct synthesis method for both additive (via deposition) and subtractive (via etching) machining for a variety of editing and prototyping applications. Nanoscale lithography mask editing is one critical area which is pushing the limits for these beam induced processing methods. Beam damage associated with liquid gallium and the recently developed gas field ion source limits their utility in lithography mask repair due to the stringent optical requirements. Thus, electron beam induced processing for mask repair of both clear and opaque defects is the method of choice. To understand the fundamental electron-solid-precursor interactions, a Monte Carlo electron-solid simulation has been developed with an appropriate precursor gas routine which emulates adsorption/desorption, surface diffusion and electron stimulated reactions. The simulation was recently modified to handle electron beam induced etching. The electron beam induced etching of silicon dioxide is studied over a range of beam energy, current, dwell times and etch precursor gas conditions to elucidate important rate limiting regimes. Furthermore, the temporal behavior of the high-aspect ratio etch process is demonstrated. Simulation results are compared to various experimental conditions to validate appropriate parameters. [Preview Abstract] |
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H1.00138: Spin-orbit interaction in Kondo regime of $\delta $-doped LaTiO$_{3}$/SrTiO$_{3}$ interface Shubhankar Das, A. Rastogi, Z. Hossain, R.C. Budhani The formation of a 2-dimensional electron gas (2DEG) at the interface of LaTiO$_{3}$/SrTiO$_{3}$ (LTO/STO) has evoked a keen interest in the condensed matter physics community due to the observation of many collective electronic phenomena in the 2DEG. In order to address some puzzling issues related to the mechanism of 2DEG formation at the LTO/STO interface and to identify the dominant scattering process that control the nature of Magnetoresistance (MR) in this system, we have used a novel approach of delta ($\delta )$ doping with iso-structural perovskite LaCrO$_{3}$ at the interface, which dramatically alters the properties of 2DEG. We have observed a reduction in the sheet carrier density with doping thickness, prominence of the resistivity upturn at low temperatures seen in LTO/STO 2DEG, shift of resistivity minimum towards higher temperature, enhancement of weak anti-localization (WAL) below 10K and strong anisotropic magnetoresistance. The observed in-plane MR is attributed to Kondo-type scattering by localized Ti$^{3+}$ moments which gets normalized by spin-orbit interaction at T \textless\ 10K. With increasing the Cr$^{3+}$ ions concentration at the interface, WAL effect becomes more prominent below 10K. [Preview Abstract] |
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H1.00139: Understanding the electronic, optical, and transport properties of (LaAlO$_3$)$_n$/(SrTiO$_3$)$_n$ multilayers K. Hunter, N. Creange, C. Constantin, J.T. Haraldsen We examine the evolution of the electronic, optical, and transport properties of (LaAlO$_3$)$_n$/(SrTiO$_3$)$_n$ multilayers (where n denotes the number of unit cells) using density functional theory with local density approximations. Using an increasing supercell, we determine multiple properties for multilayers with increasing layer thickness (n). We show a critical thickness of about n = 4 will produce a shift in the conduction and the transport properties. This is most likely related to the pushing of electrons from the LaAlO$_3$ layer into the SrTiO$_3$ layer. [Preview Abstract] |
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H1.00140: The role of oxygen vacancies of two-dimensional electron gases at LaAlO3/SrTiO3 interface Taejune Oh, Yeon Soo Kim, Sung Moon Hwang, Chan Soo Yoon, Sangik Lee, Taekjib Choi, Bae Ho Park High-mobility two-dimensional metallic states at two insulating oxides, especially LaAlO3 (LAO)/SrTiO3 (STO) interface, have provided great opportunities for novel oxide electronics. Its mechanism was explained with electronic reconstruction due to polar discontinuity or formation of oxygen vacancies at the interface, both of them have been still considered as major origins for this phenomenon. We deposit LAO layer with various thickness on STO substrate at 600${^\circ}$ and 800${^\circ}$ with pulsed laser deposition method. Both of thin films show good crystallinity and step terraced-surface morphology by x-ray diffraction and atomic force microscopy, respectively. Thickness of these films was confirmed by reflection high-energy electron diffraction. Transport properties measurement was performed by Physical Property Measurement System, however, only thin films grown at higher temperature shows high mobility properties independent on LAO thickness. Interestingly, STO substrate changed to opaque after staying for only several minutes at 800${^\circ}$ in vacuum. Obviously this change was caused from oxygen vacancies, we have observed that the substrate was recovered after annealing at 900${^\circ}$ in oxygen environment. We believe that oxygen vacancies have played important role for two-dimensional metallic state. [Preview Abstract] |
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H1.00141: Silicon Photomultiplier charaterization Leonel Munoz, Leo Osornio, Adam Para Silicon Photo Multiples (SiPM's) are relatively new photon detectors. They offer many advantages compared to photo multiplier tubes (PMT's) such as insensitivity to magnetic field, robustness at varying lighting levels, and low cost. The SiPM output wave forms are poorly understood. The experiment conducted collected waveforms of responses of Hamamatsu SiPM to incident laser pulse at varying temperatures and bias voltages. Ambient noise was characterized at all temperatures and bias voltages by averaging the waveforms. Pulse shape of the SiPM response was determined under different operating conditions: the pulse shape is nearly independent of the bias voltage but exhibits strong variation with temperature, consistent with the temperature variation of the quenching resistor. Amplitude of responses of the SiPM to low intensity laser light shows many peaks corresponding to the detection of 1,2,3 etc. photons. Amplitude of these pulses depends linearly on the bias voltage, enabling determination of the breakdown voltage at each temperature. Poisson statistics has been used to determine the average number of detected photons at each operating conditions. [Preview Abstract] |
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H1.00142: Structure and thermoelectric properties of CoSb$_{3-3X}$Ge$_{1.5X}$ Te$_{1.5X}$ (X$=$0 $\sim$ 1) Xianli Su, Xinfeng Tang, Ctirad Uher Changes in the phonon vibration spectra created by substitutions on the rings or by deforming the rings decrease the lattice thermal conductivity. In this research we focused the Ge and Te co-doped and fully compensated CoSb$_{3-3x}$Ge$_{1.5x}$Te$_{1.5x}$ skutterudite compounds for the first time. A single-phase skutterudite can be obtained with x smaller than 0.50. In comparison with a ternary skutterudite of the form CoGe$_{1.5}$Te$_{1.5}$, the order-disorder transition can be observed due to the different configuration of four-member pnicogen rings. Rietveld refinement result shows that the bond distance of Sb-Sb decreases with the increase of the Ge and Te content. With x smaller than 0.5, Ge/Te distribute randomly on the four-member near-square Sb rings. For the CoGe$_{1.5}$Te$_{1.5}$ sample, Ge Te distribute in a staggered pattern. Due to the different bonding distance and bonding angle, the near-square ring turns into a parallelogram ring, the essence of the order-disorder transition. The thermal conductivity decreases dramatically with the increasing content of Ge/Te double-doping due to the enhanced alloy scattering. [Preview Abstract] |
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H1.00143: Synthesis and characterization of high temperature thermoelectric nanocomposites based on Si$_{0.855}$Ge$_{0.12}$P$_{0.025}$ and Mg$_{1.95}$SiBi$_{0.05}$ Nikhil Satyala, Daryoosh Vashaee In thermoelectric (TE) compounds, the techniques to simultaneously attain a high Seebeck coefficient and a low thermal conductivity could be concurrently realized via nanocomposite materials systems formed by intermixing of nanostructured thermoelectric materials. These nanocomposite structures offer advantages such as low thermal conductivity ($\kappa$) via grain boundary scattering and a high Seebeck coefficient (S) by virtue of carrier filtering. We present the synthesis and characterization of a high performance nanocomposite thermoelectric based on intermixing of highly conductive n-type nanostructured Si$_{0.855}$Ge$_{0.12}$P$_{0.025}$ and Mg$_{1.95}$SiBi$_{0.05}$ in the wt({\%}) ratio of 95:05. TE samples were prepared by hot-pressing the powders at 1473 K under various conditions of pressure and holding time. The samples were characterized via microstructure analysis and measurement of thermoelectric properties over the temperature range of 300 K-250 K. Power factors of greater than 4 $\times$ 10$^{-3}$ W/mK$^{2}$ were consistently obtained by the optimization of the sintering conditions. Pertaining to the enhancement in power factor, the nanocomposite samples showed higher ZT than the nanostructured single component TE compound of Si$_{0.855}$Ge$_{0.12}$P$_{0.025}$. [Preview Abstract] |
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H1.00144: Mapping Phonons Across the Brillouin Zone of a Silicon Nanomembrane using X-ray Thermal Diffuse Scattering Gokul Gopalakrishnan, Kyle McElhinny, Martin Holt, David Czaplewski, Paul Evans Advances in the fabrication of ultrathin semiconductor membranes provide an opportunity to create novel vibrational phenomena that will ultimately yield controllable thermal and electronic phenomena not observed in bulk systems. Theoretical studies predict an order-of-magnitude reduction in thermal conductivity in silicon quantum wells relative to bulk values. The increasingly important contributions of large-wavevector phonons at the nanoscale have not been observed due to fundamental limitations of conventional probes. As a result, predictions for the behavior of confined phonons have only been experimentally investigated for small-wavevector modes near the zone center. Synchrotron x-ray thermal diffuse scattering (TDS) allows large-wavevector phonons to be probed with high momentum resolution. TDS measurements performed at the Advanced Photon Source at Argonne National Laboratory, were used to probe the entire Brillouin zone by varying the orientation of the sample relative to the incident beam and detector. Doing so yields populations of acoustic phonons in silicon nanomembranes from throughout the Brillouin zone. Results of this experiment reveal deviations from bulk-like phonon dispersions arising from confinement due to the closely separated surfaces of the nanomembrane. [Preview Abstract] |
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H1.00145: Oxygen octahedral rotation mapping in calcium titanate/strontium titanate superlattices by transmission electron microscopy Greg Stone, Jim Ciston, Ryan Haislmaier, Brian VanLeeuwen, Nasim Alem, Darrell Schlom, Venkatraman Gopalan We report the investigation of oxygen octahedral rotation mapping in calcium titanate/barium titanate superlattices epitaxially grown on LSAT (001) with transmission electron microscopy. Analysis of the images shows induced antiphase rotations of the oxygen octahedral the strontium titanate layers that is absent in the bulk material at room temperature. These rotations play a key role in breaking the centrosymmetry of the material leading to polar properties as seen by second harmonic generation. We also map the local position of the cations to provide a complete picture of any relative local displacements and the oxygen-cation-oxygen bond angles. [Preview Abstract] |
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H1.00146: Structure and shear dynamics in binary mixtures with tunable stiffness and composition Guo-Jie Gao, Yun-Jiang Wang, Shigenobu Ogata We conduct 2D molecular dynamics (MD) simulations to study the structure and relaxation behavior of highly-dense (volume fraction $=$ 0.793) binary mixtures at two temperatures, above (T $=$ 2.0) or below (T $=$ 0.2) the melting point. Particles in these mixtures interact via a pairwise n-6 Lennard-Jones (L-J) potential [Z. Shi et al. J. Chem. Phys. 135, 084513 (2011)], where n could be 8, 10 or 12 in this study. We also implement a polycrystal model where systematically increasing the number fraction of the large particle, the system changes over from crystal, polycrystal to glass [H. Shiba et al., Phys. Rev. E. 81, 051501 (2010)]. We find that lowering n increases the disorder parameter of the system at T $=$ 2.0 significantly, while the same effect is not obvious at T $=$ 0.2. Decreasing n increases the size of thermal fluctuations in both cases. Moreover, we compare the shear deformation of a polycrystal system containing either stiff grains of 10-6 L-J potential, or soft grains of 8-6 L-J potential, with that of another polycrystal system containing both kinds of grains, and address applying the results of our study to explain the enhanced ductility found in bimodal nanocrystalline copper. [Preview Abstract] |
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H1.00147: Bound electron states in skew-symmetric quantum wire intersections Subash Nepal, Liubov Zhemchuzhna, Areg Meliksetyan, Igor Bondarev We analyze the angular dependence of the lowest energy bound state for an electron trapped at the intersection of two identical narrow channels (quantum wires) crossed at an arbitrary angle. When the channels are perpendicular, such a classically unbound system is known to possess a quantum bound state [1]. We use the variational approach to study how the binding energy of the lowest bound state varies as a function of the wire intersection angle. Using two different trial wave functions, we simulate two intersection types, X-type and S-type, different in their respective channel intersection areas (diamond for the former and square for the latter). For both geometries, the binding energy generally decreases as the intersection angle deviates from the right angle. The S-type wire intersection preserves the bound state even at angles close to zero degree, as opposed to the X-type intersection. Our data supplement a theory of quantum bound states in classically unbound systems (Ref.[1]) and may be useful to interpret electron transport peculiarities in realistic systems such as semiconductor nanowire films and carbon nanotube bundles.\\[4pt] [1] R.L.Schult, et al, PRB 39, 5476 (1989). [Preview Abstract] |
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H1.00148: Impact of Be-doping on InAs/InAsSb type-II superlattices for infrared detection M. Ahoujja, S. Elhamri, T.J. Asel, E.H. Steenbergen, W.C. Mitchel, Shin Mou, G.J. Brown InAs/InAsSb superlattices (SLs) are promising materials for mid- and long-wavelength infrared (MWIR, LWIR) photodetectors due to the recently reported longer carrier lifetime than those of InAs/GaSb SLs at 77 K. However, the lifetime results are for unintentionally-doped $n$-type InAs/InAsSb SLs. Photodetectors with $n$-type absorbing regions rely on hole minority carrier transport to generate the current. This can be a disadvantage in SL photodiodes where the hole mobility in the vertical direction is extremely small at low temperatures, making collection of photo-generated minority carriers at varying depths difficult. Therefore, $p$-type SL absorber materials are preferred. However, if there is a high density of trap states or recombination sites due to the intentional dopants that limit the electron recombination lifetime, a longer hole lifetime that is traded for a higher electron mobility may result in a negative effect on the overall electrical properties, depending upon the magnitude of the lifetime and mobility changes. The carrier lifetimes and material properties of $p$-type InAs/InAsSb SLs have not been investigated yet and represent a crucial next step in developing the material for detectors. A systematic study of the impact of varying Be-dopant density levels on the InAs/InAsSb SL optical and electrical properties is performed using photoluminescence, photoconductive response, and Hall measurements. [Preview Abstract] |
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H1.00149: Plasmons in a superlattice of spherical two-dimensional electron gases Antonios Balassis, Godfrey Gumbs, Andrii Iurov, Danhong Huang A theory of collective plasma excitations in a linear periodic array of multi-shell spherical two-dimensional electron gases (S2DEGs) is presented. Coulomb coupling between electrons located on the same sphere and on different spheres is included in the random-phase approximation (RPA). Electron hopping between spheres is neglected in these calculations. The resulting plasmon-dispersion equation is solved numerically. Results are presented for a superlattice of single-wall S2DEGs as a function of the wave vector. The plasmon dispersions are obtained for different spherical radii and separations. We show that the one-dimensional translational symmetry of the lattice is maintained in the plasmon spectrum. Additionally, we compare the plasmon dispersion when the supperlatice direction is parallel or perpendicular to the axis of quantization. The S2DEG may serve as a simple model for fullerenes, when their energy bands are far apart. [Preview Abstract] |
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H1.00150: Tunneling rate in double quantum dots Igor Filikhin, Sergei Matinyan, Branislav Vlahovic We study spectral properties of electron tunneling in double quantum dots (DQDs) (and double quantum wells (DQWs)) and their relation to the geometry. In particular we compare the tunneling in DQW with chaotic and regular geometry, taking into account recent evidence about regularization of the tunneling rate [1] when the QW geometry is chaotic. Our calculations do not support this assumption. We confirm high influence of the QW geometry boundaries on the rate fluctuation along the spectrum. The factors of the effective mass anisotropy and violation of the symmetry of DQD and DQW are also considered. Generally, we found that the small violation of the symmetry drastically affects tunneling. [1] L. M. Pecora, H. Lee, D-Ho Wu, T. Antonsen, M-Jer Lee, and E. Ott, Chaos regularization of quantum tunneling rates, Phys. Rev. E, 83, 065201(R) (2011); L. M. Pecora, H. Lee, D.-Ho Wu, Regularization of Tunneling Rates with Quantum Chaos, arXiv:1205.6771. [Preview Abstract] |
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H1.00151: ABSTRACT WITHDRAWN |
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H1.00152: Structure-Induced Asymmetry of Auger Decay Rates Between Positive and Negative Trions Young-Shin Park, Wan Ki Bae, Lazaro Padilha, Istvan Robel, Jeffrey Pietryga, Victor Klimov We report spectroscopic studies of nonradiative Auger decay rates of negative (X$^{-})$ and positive (X$^{+})$ trions for three QD samples having different energy-band structures. We observe that the symmetry between X$^{-}$ and X$^{+}$ Auger decay rates observed for core-only PbSe QDs (characterized by mirror-symmetric conduction and valence bands) can be substantially distorted in CdSe/ZnS QDs, where the spectral density of valence-band states is much higher than that of the conduction-band states, leading to a relative enhancement of the X$^{+}$ decay channel. The asymmetry between X$^{-}$ and X$^{+}$ Auger rates observed for CdSe/ZnS QDs is further enhanced in thick-shell CdSe/CdS QDs wherein the hole is confined within the core, but the electron is delocalized over the entire QD, which causes a considerable reduction in the X$^{-}$ Auger decay rate. In single-dot studies of thick-shell QDs, we are able to identify photoluminescence (PL) bands of X$^{-}$ and X$^{+}$ along with that of a neutral exciton (X$^{0})$. We found that, while X$^{+}$ emission shows a short lifetime (1-2 ns) and a low quantum yield (\textless 5{\%}), X$^{-}$ PL features an increased lifetime (up to $\sim$ 10ns) and a high emission efficiency (up to $\sim$ 60{\%} of that of X$^{0})$ due to strong suppression of the X$^{-}$ Auger decay pathway, which agree well with ensemble measurements. [Preview Abstract] |
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H1.00153: Systematic Investigation of the Gold Photoluminescence in Nanoscale Antennas Toni Froehlich, Christian Schoenenberger, Michel Calame Nanoscale dipole antennas are interesting systems to study electric field enhancement effects. Within the gap between both antenna arms, a very strong electric field arises, which can stimulate molecules present in the gap. This enhanced electric field is well suited for the optical characterization of molecules, such as in surface enhanced Raman scattering. We study gold antennas which are lithographically fabricated on thermally oxidized silicon. A confocal laser microscope was used to investigate their single-photon photoluminescence (PL). The photoluminescence of a monopole antenna follows well a model proposed by Boyd \textit{et al. }[1] if the energy peak position (E$_{\mathrm{max}})$ is above the interband absorption edge (1.7--1.8 eV) of gold. The PL spectra of dipole antennas show a red-shift of E$_{\mathrm{max}}$ for decreasing gap sizes. We relate this behaviour to the increased coupling of individual arms via their optical near-field. The PL spectra are highly dependent on the shape of the antenna. For increased length or aspect ratio, we observe a decrease in the energy value E$_{\mathrm{max}}$. We can accurately fit these spectra to the model [1] and estimate the dielectric properties of the environment. Interestingly for long antennas the spectra deviate from the model and show an additional peak. The latter peak show no geometrical dependence and remains at the energy value of the interband absorption edge. Our studies set the basis for future experiments on antennas embedding optically-active molecular compounds. \\[4pt] [1] G. T. Boyd \textit{et al.}, Physical Review B (33), 7923, 1986 [Preview Abstract] |
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H1.00154: Charged-biexciton emission from single semiconductor CdSe nanocrystals Fengrui Hu, Xiaoyong Wang, Min Xiao Biexciton of a single semiconductor nanocrystal (NC) describes an intriguing electronic configuration with two electron-hole pairs present simultaneously within its excitation volume. Due to enhanced Coulomb interaction between charge carriers, biexcitons in NCs are mainly dissipated in a nonradiative Auger process on the sub-nanosecond timescale, which sets a stringent time limit within which one can characterize their optical properties. Here we performed time-tagged time-resolved measurements on single CdSe NCs under both low- and high-power excitation regimes. Under low-power excitation regime, optical emissions from both negatively- and positively-charged single excitons could be clearly resolved, together with that from neutral single excitons. The origin of positively-charged single excitons can be attributed to the electron tapping effect, while that of negatively-charged single excitons to the Auger ionization process. With the high-power excitation scheme, both negatively- and positively-charged biexcitons were additionally formed, as confirmed from the second-order photon correlation measurements. The successful preparation of charged biexcitons marks a crucial step towards the realization of efficient cascaded or entangled photon pairs from a single semiconductor NC. [Preview Abstract] |
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H1.00155: Transmission properties of 2D metamaterial photonic crystals Jorge Mej\'ia-Salazar, Nelson Porras-Montenegro By using the finite difference time domain technique, we have performed a theoretical study of the transmission properties in 2D photonic crystals composed by circular cilyndrical metamaterial rods. Numerical transmission spectra was compared with its corresponding photonic band structure in the case of an infinite periodic 2D array obtaining a very good agreement. On the other hand, we have characterized the corresponding symmetries for this system and the results were compared with its corresponding conventional plasmonic metamaterial counterpart. This work has been partially supported by the CENM-UNIVALLE. [Preview Abstract] |
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H1.00156: Disorder-induced bound states within an adatom-quantum wire system Bradley Magnetta, Gonzalo Ordonez Bound states induced by disorder are theoretically observed within a quantum wire and adatom system. The quantum wire is modeled as an array of quantum wells with random energies and exhibits Anderson Localization. By varying the energy of our adatom and adjusting the tunneling strength between the adatom and the quantum wire we observe disorder-induced bound states between the the adatom and its attached point. The characteristics of these disorder-induced bound states are greatly influenced by the site of interest on the quantum wire. Utilizing random quantum wires and disordered superlattices to produce bound states may offer flexibility in fabrication as well as provide grounds for energy transmission in photovoltaics. [Preview Abstract] |
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H1.00157: Coulomb Excitations for a Doublet of Spherical Two-dimensional Electron Gases Godfrey Gumbs, Andrii Iurov, Antonios Balassis, Danhong Huang The plasmon excitations for a pair of Coulomb-coupled non-concentric spherical two-dimensional electron gases (S2DEG's) have been investigated. Our results show that the plasmon excitations depend on the orientation with respect to the external electromagnetic probe field. The origin of this anisotropy of the inter-sphere Coulomb interaction is due to the directional asymmetry of the electrostatic coupling of electrons in excited states which depend on both the angular momentum quantum number $L$ and its projection $M$ on the axis of quantization taken as the probe ${\bf E}$-field direction. Numerical results showing the dependence of plasmon excitation energies on orientation of the doublet will be discussed as the separation between S2DEG's is varied. [Preview Abstract] |
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H1.00158: Dipole and Quadrupole Plasmon Resonances in Gold Nanoring Structures Larousse Khosravi Khorashad, Hui Zhang, Eva-Maria Roller, Tim Liedl, Alexander O. Govorov The quest for light manipulation in metallic nanostructures has grown greatly over the past decade to create novel optical devices for applications ranging from metamaterials and cloaking to optical sensing and plasmonic waveguides. Nanoring geometries, which are composed of metallic nanospheres, play an important role as the building blocks of plasmonic devices. We have shown that the plasmon resonance modes, which can be observed in absorption and scattering, not only depend on the dielectric function of the material, but also are strongly related to the size and shape of the structures and to the projection of the incident electromagnetic wave. By use of the finite element method, we have simulated ring geometries that are composed of different numbers of gold nanoparticles. The ring structures assembled experimentally have varying radii of nanoparticles and form symmetric and asymmetric geometries. This randomness in sizes and shapes influences the plasmonic spectrum of a ring, which consists of longitudinal and transverse plasmons and electric dipole and quadrupole modes. Moreover, the simulation predicts magnetic dipole radiation resulting from the circulation of current density. [Preview Abstract] |
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H1.00159: A hybrid coupling model for radiating two-resonator structures with both near-field and far-field interactions Wei Tan, Yong Sun, Zhi-Guo Wang, Hong Chen Recently increased attention is paid to optical analogue of electromagnetically induced transparency (EIT). Various classical EIT configurations have been proposed in different optical platforms, showing a great potential for such applications as compact slow-light devices and low-loss matematerials. In previous studies, only near-field coupling is considered. In fact, for more general two-resonator models, both near-field coupling and radiative interaction make contributions. We develop a hybrid coupling model that includes complex interactions to provide new insight into the coupling between two radiating resonators. It is shown that the previous classical EIT models are special cases of the hybrid coupling model. By introducing near-field and far-field coupling simultaneously, one can achieve novel electromagnetic responses. Microwave experiments are performed to realize this theoretical model, and various lineshapes are achieved by delicately tailoring the hybrid coupling. [Preview Abstract] |
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H1.00160: Visualizing light with electrons J.P.S. Fitzgerald, R.C. Word, R. Koenenkamp In multiphoton photoemission electron microscopy ($n$P-PEEM) electrons are emitted from surfaces at a rate proportional to the surface electromagnetic field amplitude. We use 2P-PEEM to give nanometer scale visualizations of light of diffracted and waveguide fields around various microstructures. We use Fourier analysis to determine the phase and amplitude of surface fields in relation to incident light from the interference patterns. To provide quick and intuitive simulations of surface fields, we employ two dimensional Fresnel-Kirchhoff integration, a technique based on freely propagating waves and Huygens' principle. We find generally good agreement between simulations and experiment. Additionally diffracted wave simulations exhibit greater phase accuracy, indicating that these waves are well represented by a two dimensional approximation. [Preview Abstract] |
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H1.00161: Surface Plasmon-Phonon Interaction in Zinc Oxide and Gold Thin Films Andrew Trenchard, Anthony Mayo, Richard Mu Surface plasmon-exciton coupling for the purpose of enhancing band edge emission has drawn a great deal of interest in recent years. ZnO and either Au or Ag nanoparticles have been used to extensively study this phenomenon. ZnO has been chosen due its wide band gap (3.37 eV) located in close proximity to the surface plasmon resonances of the Au and Ag nanoparticles and its large exciton binding energy (60 meV at room temperature), which helps with its stability at temperatures at and above room temperature. Very limited work has been done to understand surface plasmon-phonon interactions at this point, which will lead to a greater understanding of the energy transfer from metal nanoparticles to semiconductors. There has been some work done with ZnO and Ag nanoparticles showing enhanced phonon peaks due to Ag surface plasmons. In order to further understand the interaction between surface plasmons and phonons, varying thicknesses of ZnO thin films (10, 20, 30 {\&} 40 nm) were deposited by way of e-Beam Evaporation on an Au film (5 nm) on top of an SiO2 film (50 nm), both sputtered onto SiO2 substrates. These samples were then annealed at 700 C to form Au nanoparticles. The surface Plasmon-phonon interaction was studied using Raman spectroscopy and photoluminescence spectroscopy and the results will be discussed. [Preview Abstract] |
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H1.00162: Optical properties of ZnO nanotubes grown by combining electrospinning and atomic layer deposition Valentyn Smyntyna, Adib Abou Chaaya, Roman Viter, Mikhael Bechelany, Donats Erts, Philippe Miele 1D Nanostructures (NSs) have been a focus of intense research due to their novel physical properties in comparison to their bulk counterparts. The control of individual NSs properties (tunable size, shape, crystallinity and porosity) and their relative arrangements (surface density) are crucial. In this presentation, we will focus on the synthesis of ZnO nanotubes (NTs) using electrospinning combined with atomic layer deposition (ALD). The characterization of these 1D NSs will be discussed together with their optical properties. A study of absorbance and photoluminescence spectra at growth of ZnO nanotubes is reported. A structural transition from amorphous to polycrystalline state is being observed with increasing the ZnO NTs wall thickness. The study of these NSs will enable a wide range of applications in different fields such as photovoltaic, photocatalytic, gas sensing as well as molecular sensing applications. [Preview Abstract] |
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H1.00163: INSTRUMENTATION AND MEASUREMENTS |
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H1.00164: Rapid Electrolytic Conductivity Measurement Sensor Javad R. Gatabi, Zahra Rezanejad, Sayantan Das, M. Soltani Using an AC excitation signal for Electrolytic conductivity (EC) measurement, pose some limitations in cell dimensions and components as well as excitation signal amplitude and frequency. These limitations are applied to minimize the effect of double layer capacitance, Faradaic resistance, and parasitic components to increase the measurement accuracy. It reduces the sensor response time. The low frequency signal (1KHz-5KHz), in the fastest method, requires longer sampling time for sine wave fitting algorithms to estimate the amplitude of the signal. In this paper, the dynamic response of the electrochemical cell is investigated; considering the system equivalent circuit. We propose a novel EC measurement method using three pairs of electrodes, which is designed for fast measurement applications. Three excitation signals with the same frequency and amplitude but different phase are exerted on the electrolyte solution. An analog circuit is employed for fast mathematical calculation to provide an analog output signal, depending on the conductivity of the solution. The fabricated prototype is thousands times faster than traditional sensors in the same frequency range and accuracy. [Preview Abstract] |
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H1.00165: Apparatus for improved coupling of microwave energy with the tip-sample junction of a scanning tunneling microscope Chad Rhoades, Mark Hagmann, Boyd Rhoades Others couple microwave energy to or from the tip-sample junction of a scanning tunneling microscope (STM) using (1) a bias-Tee in the tip-circuit and/or sample-circuit, (2) a horn antenna, (3) a microwave cavity, (4) a coil, or (5) separate coaxial cables to the tip and sample. It is our objective to have the tip-sample junction act as a single lumped circuit element at the end of a single coaxial cable with all measurement and source connections made at the opposite end of the cable. To accomplish this, the sample is moved instead of the tip, and a section of miniature semi-rigid coaxial cable is held fixed just above the sample. The center conductor of the cable is attached to the STM tip and a fine gold wire connects the outer conductor to the sample. A novel circuit supplies the dc bias voltage, measures the dc tunneling current, and inputs or outputs microwave energy all at the opposite end of the cable. Thus, in this apparatus the microwave circuit and the DC circuit are each electrically closed in a well-defined manner without passing through the sample holder, other mechanical parts, or grounds in the system. [Preview Abstract] |
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H1.00166: ABSTRACT WITHDRAWN |
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H1.00167: Development of a 2D Photonic Crystal Biosensing Platform James Baker, Rashmi Sriram, Benjamin Miller The importance of early disease diagnosis both for initiating successful clinical treatment and preventing disease transmission continues to propel the development of rapid, ultrasensitive, label-free biosensors. Sensors that implement two-dimensional photonic bandgap crystal structures, in particular, have demonstrated the potential to achieve single-pathogen detection. To reach such high sensitivity, the architecture of the photonic crystal must be designed in a way that pathogen infiltration events are evident in the optical transmission spectrum of the crystal. Computational modeling results are useful both when designing an appropriate photonic crystal geometry and when interpreting experimental observations. Results of ongoing work are presented. [Preview Abstract] |
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H1.00168: ABSTRACT WITHDRAWN |
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H1.00169: Feedback-Enhanced Dual Optical Trap System for the Measurement of Force Applied By Contracting or Expanding Materials Joseph Craigle, Tyler Foley, Brooke Hester We have developed a technique to expand the force measurement capabilities of a dual optical trap system by implementing feedback enhancement. Using the calibrated voltage data obtained from a position sensing photodiode, it is possible to track particle displacements of only a few nanometers. By making small adjustments to the beam waist location and to the beam power based on the instantaneous displacement of the trapped bead, the trap more effectively confines the sample at the equilibrium position. The benefit is twofold in that it effectively increases the trap stiffness to counteract applied forces, and also increases the maximum measurable force particle-trap system for each trap. Using this technique, it is possible to make more precise measurements of the contracting or expanding force of a material which is covalently attached on either end to micron-sized dielectric beads. [Preview Abstract] |
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H1.00170: Capabilities for measuring the diffusivity of a single molecule by recycling it in a nanochannel Bo Wang, Lloyd Davis Analysis of the fractions of fluorescently labeled molecules with different diffusivities within a microliter drop of solution is often used for high-throughput screening of molecular binding interactions in pharmaceutical drug discovery research. Assays frequently employ fluorescence correlation spectroscopy, an ensemble technique that is able to resolve fast diffusing small ligands from those bound to much larger biomolecules with considerably slower diffusion. Single-molecule measurements have the potential to resolve species with different diffusivities and to count the numbers of molecules of each species. Single-molecule recycling in a nanochannel, which entails detection of bursts of fluorescence photons from the repeated passage of a molecule through a focused laser beam as the flow along a nanochannel is periodically alternated, can be used to determine the diffusivity of a single molecule from the fluctuations in the intervals between successive detections. We discuss Monte Carlo studies to determine favorable experimental conditions for determining single-molecule diffusivities, together with a weighted-sliding-sum photon burst detection algorithm for flow-control and maximum-likelihood based analysis of recycle times. We also discuss incorporation of the algorithms into our experimental apparatus for single-molecule recycling, which uses a LabView real-time system for photon count analysis and flow control. [Preview Abstract] |
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H1.00171: Efficacy Evaluation of Different Wavelet Feature Extraction Methods on Brain MRI Tumor Detection Nooshin Nabizadeh, Nigel John, Miroslav Kubat Automated Magnetic Resonance Imaging brain tumor detection and segmentation is a challenging task. Among different available methods, feature-based methods are very dominant. While many feature extraction techniques have been employed, it is still not quite clear which of feature extraction methods should be preferred. To help improve the situation, we present the results of a study in which we evaluate the efficiency of using different wavelet transform features extraction methods in brain MRI abnormality detection. Applying T1-weighted brain image, Discrete Wavelet Transform (DWT), Discrete Wavelet Packet Transform (DWPT), Dual Tree Complex Wavelet Transform (DTCWT), and Complex Morlet Wavelet Transform (CMWT) methods are applied to construct the feature pool. Three various classifiers as Support Vector Machine, K Nearest Neighborhood, and Sparse Representation-Based Classifier are applied and compared for classifying the selected features. The results show that DTCWT and CMWT features classified with SVM, result in the highest classification accuracy, proving of capability of wavelet transform features to be informative in this application. [Preview Abstract] |
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H1.00172: Brain MRI Tumor Detection using Active Contour Model and Local Image Fitting Energy Nooshin Nabizadeh, Nigel John Automatic abnormality detection in Magnetic Resonance Imaging (MRI) is an important issue in many diagnostic and therapeutic applications. Here an automatic brain tumor detection method is introduced that uses T1-weighted images and K. Zhang \textit{et. al}.'s active contour model driven by local image fitting (LIF) energy. Local image fitting energy obtains the local image information, which enables the algorithm to segment images with intensity inhomogeneities. Advantage of this method is that the LIF energy functional has less computational complexity than the local binary fitting (LBF) energy functional; moreover, it maintains the sub-pixel accuracy and boundary regularization properties. In Zhang's algorithm, a new level set method based on Gaussian filtering is used to implement the variational formulation, which is not only vigorous to prevent the energy functional from being trapped into local minimum, but also effective in keeping the level set function regular. Experiments show that the proposed method achieves high accuracy brain tumor segmentation results. [Preview Abstract] |
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H1.00173: Combining the utility of Digital Holography and Epi-fluorescence for localization of HEK293 cell nuclei and protein sGC Eric Sheldrake, Christopher Mann, Matthew Gage Digital Holography (DH) and Epi-fluorescence are used to analyze and localize the nuclei and the intracellular protein soluble guanylate cyclase (sGC) in human embryonic kidney 293 (HEK293) cells. DH is a non-invasive phase microscopy technique that provides three dimensional topographical information of HEK293 cells including variance of index of refraction or physical thickness. Epi-fluorescence along with fluorescent labels will be used to further studies of sGC localization. The signaling pathway including nitric oxide (NO) and sGC is studied and has been linked to various cardiovascular diseases, platelet aggregation, and variations in blood pressure via vasodilation. sGC will be labeled using an antibody and the fluorophore FITC. An understanding of how sGC interacts with its surroundings and where is localizes is vital to further research in cardiovascular disease. [Preview Abstract] |
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H1.00174: Nuclear Magnetic Resonance Gyroscope Michael Bulatowicz, Robert Griffith, Michael Larsen The navigation grade micro Nuclear Magnetic Resonance Gyroscope (micro-NMRG) being developed by the Northrop Grumman Corporation (NGC) has concluded the fourth and final phase of the DARPA Navigation Grade Integrated Micro Gyro (NGIMG) program. Traditional MEMS gyros utilize springs as an inherent part of the sensing mechanism, leading to bias and scale factor sensitivity to acceleration and vibration. As a result, they have not met performance expectations in real world environments and to date have been limited to tactical grade applications. The Nuclear Magnetic Resonance Gyroscope (NMRG) utilizes the fixed precession rate of a nuclear spin in a constant magnetic field as an inertial reference for determining rotation. The nuclear spin precession rate sensitivity to acceleration and vibration is negligible for most applications. Therefore, the application of new micro and batch fabrication methods to NMRG technology holds great promise for navigation grade performance in a low cost and compact gyro. This poster will describe the history, operational principles, design, and demonstrated performance of the NMRG including an overview of the NGC designs developed and demonstrated in the DARPA gyro development program. [Preview Abstract] |
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H1.00175: Auto-tuning for NMR probe using LabVIEW Carmen Quen, Stephanie Pham, Oscar Bernal Typical manual NMR-tuning method is not suitable for broadband spectra spanning several megahertz linewidths. Among the main problems encountered during manual tuning are pulse-power reproducibility, baselines, and transmission line reflections, to name a few. We present a design of an auto-tuning system using graphic programming language, LabVIEW, to minimize these problems. The program uses a simplified model of the NMR probe conditions near perfect tuning to mimic the tuning process and predict the position of the capacitor shafts needed to achieve the desirable impedance. The tuning capacitors of the probe are controlled by stepper motors through a LabVIEW/computer interface. Our program calculates the effective capacitance needed to tune the probe and provides controlling parameters to advance the motors in the right direction. The impedance reading of a network analyzer can be used to correct the model parameters in real time for feedback control. [Preview Abstract] |
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H1.00176: Quantum and classical theory for the phonon bath in atom-surface scattering: Application to the Cu(111) system Shauli Daon, Salvador Miret-Artes, Eli Pollak Abstract Inspired by the semiclassical perturbation theory of Hubbard and Miller [J. Chem. Phys.80, 5827 (1984)10.1063/1.446609], we derive explicit expressions for the angular distribution of particles scattered from thermal surfaces. At very low surface temperature, the observed experimental background scattering is proportional to the spectral density of the phonons. The angular distribution is a sum of diffraction peaks and a broad background reflecting the spectral density. The theory is applied to measured angular distributions of Ne, Ar, and Kr scattered from a Cu(111) surface [1]. Abstract The theory is further explored for the study of the effects of the phonon bath in atom-surface scattering. [2] The theory is utilized to derive the angular distribution in three ways. First, we modify the angular width of the incident beam to investigate the effect of beam collimation. [2,3] Second, a continuum limit expression is obtained for a classical phonon bath. Third, numerical discretization is applied to the phonon bath, to solve for all bath modes. [Preview Abstract] |
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H1.00177: Development and Characterization of Dynamic Light Scattering Instrumentation to Determine Nanoparticle Size Thomas Volpe, C. Jensen, C. Di Fatta, P. McAtee, M. Schulze, S.M. Lev, J.R. Simpson Dynamic Light Scattering (DLS) provides a high-throughput and accurate measurement of particle sizes for monodisperse (MD) spherical nanoparticles (NPs). We report on the development and characterization of homebuilt DLS instrumentation to measure the size of MD NPs, including polystyrene, gold, and ZnO NPs. HeNe and Argon-ion lasers comprise the excitation sources for the scattering experiment. We have evaluated an avalanche photodiode detector for the acquisition of the scattered light. Time averaging and time-autocorrelation electronic signal detection and analysis provides a measure of the translational diffusion coefficient, which for MD and spherical particles allows for determination of the NP radius. ZnO NPs will be synthesized using several techniques and compared to those produced commercially. We have characterized our instrumentation by measuring the size of commercially-produced gold and polystyrene in the range of 10\,nm to 200\,nm and found excellent agreement ($\pm 5\%$) with reported values. The synthesized particles are expected to range in diameter from 200\,nm down to 20\,nm. After size characterization, the ZnO NPs will be employed in ongoing toxicity studies. [Preview Abstract] |
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H1.00178: In-situ Light Scattering Measurements of FeOOH spindles in solution Philip Dee, Olga Dement'eva, Victor Rudoy, Kiril Streletzky Characterizing spindle-shaped (nanorice) particles of iron (III) oxyhydroxide (FeOOH) with the Depolarized Dynamic Light Scattering (DDLS) and other light scattering techniques provides an accurate and reliable estimate for nanoparticle size, shape, and dynamics in a native colloidal solution. Specific applications such as targeted synthesis of core/metal nanoshell structures for techniques such as laser photothermal therapy suggest that there's advantage to in situ measurements of FeOOH nanoparticles. FeOOH can also serve as a standard/control system for light scattering characterization of hard-to-image soft-matter particles of certain anisotropic geometries. The analytical geometrical models of prolate spheroid and short cylinder were employed to analyze rotational and translational light scattering data yielding nanoparticle structure and dynamics. The methods which utilized a straight cylinder model created by de la Torre, proved to be most consistent with size distributions obtained by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). Three independently synthesized FeOOH colloidal solutions with particle size aspect ratios of 3.5-4.6 produced the apparent size estimates that fall within 1 standard deviation of TEM and SEM results. [Preview Abstract] |
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H1.00179: Temporal characterization of electron pulses with 10fs resolution Thomas Juffmann, Gunnar E. Skulason, Catherine Kealhofer, Mark A. Kasevich Aiming for quantum control of free electrons it is essential to be able to characterize electron pulses in space and time. We are developing an experimental technique that enables the measurement of the temporal profile of an electron pulse with a resolution of about 10fs. A sub 10fs Ti Sapphire oscillator is used to trigger the emission of electrons from a metal tip. The electrons are subsequently accelerated towards an electrode, where they pass through nanometric apertures. Within these apertures, the electrons can interact with evanescent optical fields created with the same Ti Sapphire laser. If the electron pulse and the laser pulse coincide spatially and temporally, their interaction will influence the energy spectrum of the electrons. The temporal cross correlation can then be determined by scanning the time delay between the two laser pulses. We report on the progress of our experimental implementation of this technique, which will be useful in ultrafast electron diffraction experiments. [Preview Abstract] |
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H1.00180: An Automated, High-Throughput System for GISAXS and GIWAXS Measurements Eric Schaible, Jessica Jimenez, Eun Hee Lim, Matthew Church, Christina Yee, Polite Stewart, Alastair MacDowell, Dula Parkinson, Ed Domning, Lee Yang, Steven Alvarez, Alexander Hexemer Grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS) are important techniques for characterizing thin films.~ In order to meet rapidly increasing demand, the SAXSWAXS beamline at the Advanced Light Source (beamline 7.3.3) is implementing a fully automated, high-throughput system to conduct SAXS, GISAXS and GIWAXS measurements.~ An automated robot arm will transfer samples from a holding tray to a measurement stage.~ Intelligent software will align each sample in turn, and measure each according to user-defined specifications.~ Users will be able to mail in trays of samples, and will be able to monitor and control their experiments remotely.~ Data will be pipelined to the NERSC supercomputing facility, and will be available to users via a web portal that facilitates highly parallelized analysis. [Preview Abstract] |
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H1.00181: Reconstruction of tip-surface interactions with multimodal intermodulation atomic force microscopy Stanislav Borysov, Daniel Platz, Astrid de Wijn, Daniel Forchheimer, Eric Tol\'en, Alexander Balatsky, David Haviland We present a developed theoretical framework for reconstructing tip-surface interactions using the intermodulation technique when more than one eigenmode is required to describe the cantilever motion. Two particular cases of bimodal motion are studied numerically: one bending and one torsional mode, and two bending modes. We demonstrate the possibility of accurate reconstruction of a two-dimensional conservative force field for the former case, while dissipative forces are studied for the latter. [Preview Abstract] |
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H1.00182: Beyond 5 nm: high resolution in low energy photoemission electron microscopy through variable spherical and chromatic aberration correction J.P.S. Fitzgerald, R.C. Word, R. Koenenkamp Correcting spherical and chromatic aberration in electron optics remains a fundamental obstacle to high resolution microscopy. This is particularly true for low energy photoemission electron microscopy (PEEM) in which electrons are emitted with a wide range of energies, demanding greater chromatic aberration correction. Based on the success of a simple electrostatic hyperbolic mirror, we are developing a multi-electrode mirror that will provide variable chromatic and spherical aberration correction. Following the same hyperbolic geometry allows analytic solutions for the spherical and chromatic aberration coefficients, allowing the optimization of other geometric parameters. The final, optimized design was compared against simulation and found to differ by less than 5{\%} over the operating voltage ranges. We are currently working on installation of this new correction system and report on progress. [Preview Abstract] |
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H1.00183: Developing a Quantum Electron Microscope Christoph Kohstall, Brannon Klopfer, Josh Francis, Gunnar Skulason, Thomas Juffmann, Mark Kasevich We develop a new electron microscope based on the interaction-free measurement principle [1,2]. Such a Quantum Electron Microscope (QEM) [3] may enable imaging of biological samples with radiation doses so small that they are non-lethal. The realization of the QEM will require precise control over the quantum motion of free electrons. On this poster, we discuss our approach to build a QEM including the realization of an electron resonator and an electron amplitude beam-splitter. On top of the QEM application, these developments will advance the electron analogue to photon quantum optics.[1] A. C. Elitzur and L. Vaidman, Found. Phys. 23, 987 (1993)[2] P. Kwiat, H. Weinfurter, T. Herzog, A. Zeilinger, and M. A. Kasevich, Phys. Rev. Lett. 74, 4763 (1995)[3] W. P. Putnam and M. F. Yanik, Phys. Rev. A 80, 040902(R) (2009) [Preview Abstract] |
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H1.00184: Image quality metric based on mutual information of image features Mohammad Haghighat, Masoud Amirkabiri Razian Objective image quality assessment has always been a challenging issue among image processing scientists. Here, a novel image quality metric based on mutual information of image features is presented. The proposed metric calculates the amount of information that one image contains about the other. Normalized feature vectors extracted from the test and reference images represent the considered information as the marginal probability distributions. In order to use the mutual information we need not only the marginal probability distributions but also the joint distribution between two images. In this work, Nelsen's method is employed to estimate the joint probability distribution from marginal distributions using the correlation between two feature vectors. Experimental results and comparisons with other well-known full-reference metrics like SSIM, MSSIM, FSIM and SFF certify the soundness of our proposed metric. [Preview Abstract] |
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H1.00185: Evaluation of the optical flow methods on facial expression classification Mohammad Haghighat, Masoud Amirkabiri Razian Facial expression recognition is an important issue in modern human computer interaction (HCI). In this work, the performance of optical flow in tracking facial characteristic points (FCPs) is examined and it is used as an application of facial expression classification. FCPs are extracted using active appearance model (AAM), and the features selected to the classification are the perceived movements of the FCPs and the changes in geometric distance between them. This work compares four different optical flow methods on FCP tracking: normalized cross-correlation, Lucas-Kanade, Brox, and Liu-Freeman. Nearest neighborhood rule is used for the classification. Evaluations are done on the Cohn-Kanade (CK$+)$ database for five prototypic expressions. Experimental results show that Lucas-Kanade method outperforms the other three optical flow methods. This has been assessed based on ground truth established in CK$+$ database. [Preview Abstract] |
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H1.00186: An Integrated Data Driven Reconstruction and Molecular Dynamics Simulation for Lattice Structure in Atom Probe Tomography Joaquin Peralta, Kaustubh Kaluskar, Claudia Loyola, Krishna Rajan Atom Probe Tomography (APT) is an experimental technique that gives 3D atomistic spatial resolution of a material specimen. Actual APT limits the detection of atoms around 50\%. In this work, we propose a new reconstruction methodology, which relaxes some requirements of the actual procedures, and can be applied to regions across grain boundaries or amorphous regions. This methodology consist of four main steps: (i) the use of an initial structure which is provided by APT IVAS Software; (ii) the elimination of overlapping atoms; (iii) the detection of atomic vacancies with the incorporation of missed atoms; and (iv) the use of classical molecular dynamic (MD). As a bed-test, we show a tungsten sample structure. We analyze it using structural properties, as Radial Distribution function, to detect overlapped atoms. The vacancies detection algorithm is used to identify atomic vacancies in a crystalline or amorphous region. This particular feature is very helpful to identify zones like grain boundary regions. Once the atoms are relocated in the structure, a classical MD is carried out in order to improve the atomic structure, shape and morphology of the data. The final result, provided by the MD simulation, is characterized and compared with the initial structure. [Preview Abstract] |
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H1.00187: Measuring In-Plane Thermal Conductivity of Anisotropic Thin-films Misha Rodin, Shannon Yee Polymer thermoelectrics (TEs) are a promising alternative to traditional TEs due to low cost and scalability. Higher efficiency polymer TEs can be realized by control of in-plane electrical and thermal properties. This specifically requires a non-contact technique that can probe the thermal conductivity of highly anisotropic films. Current conductivity measurements of thin-films rely on periodic heating of a semi-infinite solid. The periodic heating causes surface temperature fluctuations, which depend on the thermal and physical properties of the material. Presented here is our progress in developing a frequency-domain thermoreflectance (FDTR) technique to measure in-plane thermal conductivity of highly anisotropic films. Traditional FDTR uses a circular laser spot for heating and is insensitive to the effects of lateral heat flow. By modifying the heating laser spot from a circle to an annulus, the temperature fluctuations inside the annulus perimeter are significantly influenced by lateral heat flow. The probe laser can scan within the annulus, making this technique sensitive to both the in-plane and through-plane properties. Additionally, this technique can be used at high heating frequencies to measure phonon MFP contributions to the thermal conductivity in both directions. [Preview Abstract] |
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H1.00188: Investigation of anisotropic thermal transport in polymers using infrared thermography David Nieto Simavilla, David Venerus, Jay Schieber During manufacturing, the anisotropic nature of thermal transport in flowing polymers plays an important role in the final properties of materials. In our laboratory, we have investigated anisotropic thermal conductivity in polymers subjected to deformation using an optical technique based on Forced Rayleigh Scattering (FRS). For over a decade, our setup has been the only one capable of testing the linear relationship between anisotropy in thermal conductivity and stress, known as the stress-thermal rule. In order to overcome some of the limitations in the optical properties of materials inherent to FRS, we have recently developed a complementary technique based on infrared thermography (IRT). We validate IRT technique by comparing measurements of anisotropy in thermal conductivity on crosslinked networks against those obtained with FRS. The main advantage of IRT method is that, it allows us to study optically thick materials, including polymers that are prone to strain induced crystallization. Additionally, examination of IRT transient state experiments enables us to study the effect of deformation on other properties such as specific heat capacity. [Preview Abstract] |
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H1.00189: Perturbative magnetoresistance technique used to investigate FM/AF coupled bilayers Alexandre Oliveira, Ricardo da Costa, Abner Melo, Carlos Chesman In this study we introduced modifications to a collinear four probe magnetoresistance set-up in order to measure magnetic properties that can only be sensed by techniques based on magnetization perturbation. In addition to the applied DC magnetic field (H$_{dc})$, in magnetoresistance experiments, a small and quasi-static alternating magnetic field (h$_{ac}$, less than 10 Oe and around 800 Hz) is applied perpendicularly, both parallel to the sample plane. Due to Zeeman interaction, hac drives sample magnetization to oscillate slightly around its equilibrium position. Although we apply only DC current (few mA), the detected voltage carries DC and AC components. The DC voltage component provides information on magnetoresistance (MR) and the AC component is called perturbative magnetoresistance (PMR). We successfully demonstrated that the PMR signal is proportional to the first derivative of resistance with respect to h$_{ac}$. Using this technique and a phenomenological model that takes into account the relevant free energy terms of FM/AF coupled bilayers, we were able to study reversible and irreversible magnetization rotation processes in these magnetic systems. With respect to magnetic anisotropy, we investigated rotatable anisotropy, proposed by McMichael \textit{et al} [1] and Geshev \textit{et al }[2]. [1] R. D. McMichael, M. D. Stiles, P. J. Chen, and W. F. Egelhoff, Jr., Phys. Rev. B, 58, 8605 (1998); [2] J. Geshev, L. G. Pereira, and J. E. Schmidt, Phys. Rev. B, 66, 134432 (2002). [Preview Abstract] |
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H1.00190: Bolometric calibration of microwave power in low temperature systems Sergey Vitkalov, Sean Byrnes, Scott Dietrich We present a simple and effective method for ascertaining the true MW field applied to small samples mounted on a cold finger in vacuum in low temperature systems. As the MW power delivered to the sample through a coax is dissipated over an impedance-matching terminal resistor, the cold finger requires less power from the temperature control system. By monitoring the control system voltage with and without microwave power, the microwave electric field delivered to sample can be obtained for a wide range of microwave frequencies. The proposed technique accurately obtains the microwave field delivered to the sample without the requirement of further corrections due to dissipation and/or reflection of the microwave elsewhere in the system. [Preview Abstract] |
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H1.00191: Construction of Tunnel Diode Oscillator for AC Impedance Measurement J.H. Shin, E. Kim We construct a tunnel diode oscillator (TDO) to study electromagnetic response of a superconducting thin film. Highly sensitive tunnel diode oscillators allow us to detect extremely small changes in electromagnetic properties such as dielectric constant [1], ac magnetic susceptibility [2] and magnetoresistance [3]. A tunnel diode oscillator is a self-resonant oscillator of which resonance frequency is primarily determined by capacitance and inductance of a resonator. Amplitude of the signal depends on the quality factor of the resonator. The change in the impedance of the sample electromagnetic coupled to one of inductors in the resonator alters impedance of the inductor, and leads to the shift in the resonance frequency and the change of the amplitude.\\[4pt] [1] C. Boghosian, H. Meyer, J.E. Rivers, ``Density, Coefficient of Thermal Expansion, and Entropy of Compression of Liquid Helium-3 under Pressure below 1.2K,'' Phys. Rev 146, 110 (1966).\\[0pt] [2] B. Dalrymple and D. Prober, ``Radio-frequency susceptibility apparatus for measuring small superconducting samples,'' Rev. Sci. Instrum 55, 958 (1984). \\[0pt] [3] G. J. Athas, J. S. Brooks, S. J. Klepper, S. Uji, and M. Tokumoto, ``Tunnel diode oscillator application to high sensitivity de Haas--van Alphen and superconducting critical field studies of anisotropic organic conductors,'' Rev.Sci. Instrum 64, 3248 (1993). [Preview Abstract] |
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H1.00192: Low-Energy Signals in a NaI(Tl) Scintillation Detector Gulden Othman Dark matter is one of the most captivating topics in physics research today. The most widely received candidate for dark matter is of the class called Weakly-Interacting Massive Particles, or WIMPs. There are currently several experiments being conducted by collaborations worldwide with the goal of detecting WIMPs, and to determine their properties. Many of these experiments involve, or have involved, the use of scintillation detectors, such as CsI or NaI(Tl). Thus it is essential to know the response of a scintillator to low energy nuclear recoils due to a WIMP-Nuclear collision. Such knowledge aids in the removal of backgrounds by discriminating between electromagnetic and nuclear-recoil energy depositions. This project provides an analysis of experimental data collected as a result of interactions between a neutron beam and a NaI scintillator. [Preview Abstract] |
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H1.00193: SURFACES, INTERFACES ADN THIN FILMS |
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H1.00194: Current perpendicular-to-plane (CPP) metal-to-insulator transition in BaTiO3/LaAlO3/SrTiO3(100) hetero-interface Jonghyun Song, Seungran Lee, Jinhee Kim The transport properties of ultra-thin BaTiO3 (BTO) films have been studied by employing a quasi 2-dimensional electron gas system (q2-DEG) of LaAlO3/SrTiO3 (LAO/STO) interface as the bottom electrodes. The LAO/STO layer is found to serve as the conducting electrode down to 2 K due to formation of conducting paths inside the LAO layer on to the metallic LAO/STO interface. Despite of the ultra-thin thickness of BTO films, current perpendicular-to-plane (CPP) show clear metal-to-insulator transitions with decreasing temperatures while the transition temperatures vary in the ranges of 150-310 K. The metallic behavior of the ultra-thin BTO can be understood with dominant electron-electron scattering, while the insulating state can be explained with variable-range-hopping conduction probably due to the dominant role of localized defect states in the BTO layers. The electrical properties are further investigated by increasing applied bias voltages. Our studies with combined ultra-thin ferroelectric and q2-DEG provide important clues to applicable devices with 2-dimensional carriers and/or ultra-thin ferroelectric layers with plausible explanations for their conduction mechanism. [Preview Abstract] |
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H1.00195: Preparation and Characterization of SrCoO3 Heterostructures Grown along the (111) Direction Minhui Hu, Fang Yang, Jiandong Guo The Topological Insulators (TIs) have attracted much more attention in the research of condensed matter physics due to their promising application potentials [1, 2]. Recent theoretical work has discovered topological insulating behavior in heterostructures of transition-metal oxides (TMOs), and demonstrated that the perovskite-type TMOs films grown along the high-symmetry (111) direction were very likely to realize topological phases [3]. Even that, it is still a great challenge to grow well-suited TMOs films along the (111) direction to display the topological insulating property. In this work, we focus on preparing SrCoO3 thin films on SrTiO3 (111) substrates by UHV pulsed-laser deposition (PLD) equipped with in-situ monitoring by RHEED. After that we will discuss about the structural properties and characterization of SrCoO3 (111) by XRD, XPS and transport measurements, etc. Based on the electron-phonon coupling phenomenon, we will explore the possible topologically non-trivial phase of SrCoO3 (111). Our preliminary results may open new way to explore the topological effects from TMOs heterostuctures. [1]Z. Fang et al. Science 329, 5987 (2010). [2]Q.-K. Xue et al. Science 340,167 (2013). [3]S. Okamoto et al. Nature communications 2, 596 (2011). [Preview Abstract] |
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H1.00196: In-Situ Coherent Grazing Incidence Small Angle X-ray Scattering (Co-GISAXS) Studies of Surface Fluctuations of Sputter Deposited WSi$_{2}$ using X-ray Photon Correlation Spectroscopy (XPCS) Som Dahal, Jeffrey Ulbrandt, Randall Headrick, Alexander DeMasi, Karl Ludwig We performed Coherent Grazing Incidence Small Angle X-ray Scattering (Co-GISAXS) studies of surface dynamics during magnetron sputtering deposited WSi$_{2}$ amorphous thin films. The local dynamics of surface fluctuations was studied by X-ray Photon Correlation Spectroscopy (XPCS) in the late time regime where the static GIXAXS stops evolving. Our studies reveal that the correlation time of the sputtered species varies as a power law with the in-plane momentum transfer. The experimentally obtained results are compared with predictions from continuum models of surface growth. [Preview Abstract] |
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H1.00197: Evidence of thermal heating in the low temperature resistive switching of V$_{2}$O$_{3}$ microbridges Mariela Menghini, Leander Dillemans, Karen Levrie, Pia Homm, Chen-Yi Su, Ruben Lieten, Tomas Smets, Jean-Pierre Locquet Vanadium sesquioxide (V$_{2}$O$_{3}$) is a strongly correlated material that exhibits a metal-insulator-transition (MIT) at low temperatures. The electrical triggering of this transition could result in an exciting new category of applications, such as resistive switching-based memories and field-effect transistors. We have fabricated V$_{2}$O$_{3}$ microbridges by combining MBE growth with UV lithography and etching.The MIT is studied in microbridges with different length/width aspect ratios. We found that the size of the MIT is largest for the widest and shortest microbridges. We discuss the influence of device processing in the observed behavior. We have also measured voltage-current characteristics (VIs) of the microbridges at different temperatures across the MIT. At intermediate temperatures we observe a sudden change to a more resistive state while the current is swept continuously. The only way to switch back to an insulating state is by thermal cycling. At sufficiently low and high temperatures the VIs are smooth. We have estimated the power transferred to the device by the applied current in order to understand this behavior in terms of local Joule heating. The distribution of size of the resistance jumps and the values of voltage and current at which these jumps occur are studied as a function of width and length of the microbridge. [Preview Abstract] |
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H1.00198: Metal-Dielectric Sidewall Scattering Measurements with Ballistic Electron Emission Microscopy Chris Durcan, Robert Balsano, Vincent Labella As the spatial dimensions of metal lines shrink below 50 nm their resistance increases due to increased electron scattering from sidewalls and grain boundaries. Conventional methods of determining metal line resistance use current voltage measurements which averaged over the entire volume and need phenomenological modeling to extract the sidewall scattering parameter. Ballistic electron emission microscopy (BEEM) is a scanning tunneling microscopy (STM) technique that can measure electron transport through materials and interfaces with nanometer spatial resolution. This work will describe our progress on performing BEEM measurements on lithographically patterned 40-nm-wide trenches in a dielectric film on a semiconductor that are filled with a metal. Electron beam lithography is utilized to pattern the structure and both BEEM imaging and spectroscopy is performed in an attempt to locally measure scattering due to sidewalls. The ultimate goal is to map electron transport throughout a metal line/sidewall structure to provide nanoscale insight into the sources of electron scattering. [Preview Abstract] |
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H1.00199: Growth of Cu-Ni Nanostructures on Cu(111): A Molecular Dynamic Study Berk Onat, Sondan Durukanoglu We have studied energetics and growth mechanisms on nanostructures both using molecular dynamic simulations and total energy calculations to understand the nature of Ni and Cu growth on Cu(111) surface. The interactions between the atoms in the systems are defined using a many-body type potential developed for Cu-Ni alloys within the EAM formalism. Our simulations on Cu-Ni systems with mono/double-layer Ni islands on Cu(111) show that Cu atoms could migrate to Ni islands and decorate the bottom and even the upper layer of Ni islands. Furthermore, we find that the formation of the islands is governed by the nature of the decoration process. From total energy calculations we also discuss the governing diffusion mechanisms for the formation of Cu-Ni islands on Cu(111). [Preview Abstract] |
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H1.00200: Hybrid graphene-catalyst nanostructures: elucidating the nature of the interface Georgi Diankov, Jihwan An, Joonsuk Park, Fritz Prinz, David Goldhaber-Gordon There has been intense research into developing and characterizing new electrochemically active materials consisting of nanosized catalysts and thin films on various substrates. The desirable characteristics of nanoscale catalysts, such as low mass loading, high efficiency and chemical stability, directly depend on the atomic-scale nature of the interface between the catalyst particles and their substrates. We synthesize and characterize one such model interface, that between high-quality graphene surfaces and Pt nanocrystals grown directly on the graphene. We observe an atomically sharp interface and a high degree of crystalline order. In particular, we analyze the chemical nature of the interface with probe-corrected STEM-EELS at 80 kV and aim to understand the chemical nature of the interface. The study points to novel ways of engineering interfaces for nanocatalysis. [Preview Abstract] |
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H1.00201: Concentration dependence of nanoparticle surface coverage for ionic self-assembled monolayers Vincent Kim, Brian Simpson, Andrew Seredinski, Eric Schwen, Dan Mazilu, Irina Mazilu We investigate the concentration dependence of the surface coverage of thin films that consist of silica nanoparticles deposited on the substrates via the ISAM (ionically self-assembled monolayers) technique. Several experiments were conducted in order to investigate the factors that affected the quality of the coatings and one significant factor observed was the concentration of the colloidal silica solution. Using SEM micrographs, we analyzed the surface coverage and compared it to the analytical results obtained using a cooperative sequential adsorption model. The results we obtained matched the linear relation between particle density and the inverse of the concentration predicted by the theory.~ [Preview Abstract] |
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H1.00202: Oxygen-poor phase observed during plasma-sprayed physical vapor deposition of zirconia coatings Brian Good, Bryan Harder When cubic zirconia is deposited using Plasma Spray-Physical Vapor Deposition (PS-PVD) under oxygen-poor conditions, a metastable phase is observed. We describe a combined experimental and computational approach aimed at determining the structure and composition of the phase. X-Ray analysis indicates that the phase exhibits cubic symmetry, and it is also found to be electrically conductive, in contrast to cubic zirconia, which is electrically insulating. We have performed electronic structure calculations aimed at identifying the metastable phase. Three cubic candidate ZrO structures were identified, and the lattice constants were optimized for each. The lowest-energy structure was found to be the NaCl structure. Projected density of states calculations show that the material is conductive, with conduction occurring within the Zr 4s band. Potential technological uses for the phase are discussed. [Preview Abstract] |
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H1.00203: Probing the buried C$_{60}$/Au(111) interface with atoms Lin Tang, Yangchun Xie, Quanmin Guo To characterize the C$_{60}$/Au(111) interface, we send Au atoms ``diving'' through the C$_{60}$ layer and observe their behavior at the interface. Our observations show that the interfacial diffusion of gold atoms and the nucleation of small Au islands at the interface are strongly dependent on the local C$_{60}$-Au(111) bonding which varies from one domain to another. The contrast-disordered domain consisting of a large fraction of molecules bonded to Au vacancies has a special structure at the interface allowing Au atoms to be inserted beneath the bright-looking molecules while the dim molecules present a much stronger resistance to the diffusing Au atoms. This leads to the formation of isolated Au islands with discrete sizes, with the smallest island just about 1 nm across. [Preview Abstract] |
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H1.00204: Low Temperature Energy Phase Diagrams of Dimer Adsorption on Square Nanotubes with Repulsive First-Neighbor Interactions Alain Phares, David Grumbine, Jr We consider dimer adsorption on infinitely long square nanotube surfaces with increasing diameter which, when keeping the lattice constant fixed, corresponds to an increasing number $M$ of atomic sites in the normal section of the nanotube. We present the low temperature energy phase diagram of the system which is generated assuming repulsive first-neighbors and arbitrary second-neighbor interactions. The occupational characteristics of the system are the coverage, $\theta_0$, and the numbers of first- and second-neighbors per sites, $\theta$ and $\beta$. Crystallization patterns (phases) occur at values of the set \{ $\theta_0$, $\theta$, $\beta$ \} given explicitly as functions of $M$. The regions of the phase diagram in which the phases are found have been determined for any $M$, allowing an exact extrapolation to the infinite $M$ limit. [Preview Abstract] |
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H1.00205: Investigation of CaMnO$_{3}$ Epitaxial Thin Films by High Resolution X-ray Diffraction and Atomic Force Microscopy Grace Yong, Rajeswari Kolagani, Zoey Warecki, Christopher Stumpf, David Schaefer, Madhana Sunder CaMnO$_{3}$ is known for its high catalytic activity for oxidation reactions. As the surface characteristics are important in determining the catalytic properties of thin films, we are investigating the structural and morphological characteristics of epitaxial thin films grown by Pulsed Laser Deposition. Film structure and morphology are sensitive to variations in the deposition conditions such as the deposition oxygen pressure. In CaMnO$_{3-\delta }$, oxygen vacancies are found to be ordered in such a manner as to preserve most of the structural features of the parent stoichiometric perovskite. We are characterizing the films using high resolution x-ray diffraction in the reflectivity mode (low angle measurements) and using Atomic Force Microscopy. We will study Kiessig fringes as a function of film growth conditions. The film thickness can be determined from the period of the fringes and roughness can be characterized by the angular range of the fringes. We will compare the surface roughness obtained by x-ray reflectivity with those obtained using AFM (atomic force microscopy). [Preview Abstract] |
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H1.00206: Growth environment driven physical property changes of ZnO films S.H. Lee, Y.E Jeong, H.K. Kim, D.Y. Lee, J.S. Bae, W.J. Lee, K.H Park, S.D. Bu, Sungkyun Park The growth temperature and post-annealing dependent on the thermal stress of undoped ZnO films and oxygen partial pressure dependent physical properties of Pdoped ZnO films were investigated. As the growth temperature increased, the lattice constant increased and approached the bulk value, suggesting a decrease in interfacial strain between the substrate and thin film. For the post annealed films, the interfacial strain decreased further and was close to the bulk value regardless of the post annealing environments. The optical band gap varied according to the growth temperature and post annealing environments due to a decrease in the interfacial strain effect. In the case of the variation of oxygen partial pressure during the growth, the degree of crystallinity and the amount of oxygen vacancies in the films decreased with oxygen partial pressure. All films showed $n$-type except for a film grown at 100 mTorr, which exhibited $p$-type. The optical band gap energy also changed with the oxygen partial pressure. The feasible microscopic mechanism of conductivity conversion is explained in terms of the lattice constant, crystallinity, and relative roles of the substituted phosphorous in the Zn-site and/or oxygen vacancies depending on the oxygen partial pressure. [Preview Abstract] |
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H1.00207: Vibrational spectrum and stability of the long-debated models for the ($\sqrt{7} \times \sqrt{7}$)$R19\circ $ phase of S/Cu(111) Marisol Alcantara Ortigoza, Maral Aminpour, Talat S. Rahman Recently, the structure of the copper sulfide overlayer formed on Cu(111) upon sulfur exposure has attracted attention because it serves as a substrate to form MoS$_{2}$ monolayers and MoS$_{\mathrm{X}}$ nanostructures in a controlled manner, which may have numerous technological applications. In the past, at least eight experimental techniques have been used to characterize the $(\sqrt 7 \times \sqrt 7 )R19\circ $Cu-S overlayer on Cu(111) and to support or refute a large number of possible models but, as yet, at least three models are still in dispute. In this study, we provide firmer arguments to resolve the structure of CuS/Cu(111) at the atomic scale. Specifically, we perform density-functional-theory calculations of the total energy and the vibrational spectrum of the proposed structures to (1) attest their dynamical stability; (2) compare their thermodynamic stability as obtained from the total free energy; and (3) provide the vibrational frequencies that uniquely fingerprint these structures and which may serve for further experimental confirmation or refutation. [Preview Abstract] |
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H1.00208: Tuning Rhenium Surface Morphology by Kinetic Control of Adsorbates Hao Wang, Xiaofang Yang, Grant Junno, Wenhua Chen, Bruce Koel, Robert Bartynski, Payam Kaghazchi, Timo Jacob The surface morphology of Re($11\bar{{2}}1)$ can be tailored on the nanometer scale by careful control of adsorbate species, adsorbate coverage, and surface temperature. We have found that drastically different morphologies of three-sided pyramids versus two-sided ridges can be induced by adsorption of either carbon or nitrogen, respectively. These structures expose well-defined nanoscale facet planes with controlled size and can serve as model catalysts and catalyst supports. The nitrogen-induced ridges are formed by $(13\overline 4 2)$ and $(31\overline 4 2)$facets while the carbon-induced pyramids by ($11\bar{{2}}0)$,($01\bar{{1}}1)$ and ($10\bar{{1}}1)$ facets. We also observed a (2 $\times$ 1) reconstruction of Re($11\bar{{2}}1)$ at low nitrogen coverage which acts as a precursor state for nitrogen-induced faceting. DFT calculations provide an atomistic understanding of facet formation in terms of the geometries and energetics of adsorbates on the substrate and facets as well as corresponding surface phase diagrams. [Preview Abstract] |
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H1.00209: Benzene Adsorption on (110) Surfaces of Transition Metals: Role of van der Waals Interaction and Substrate Chemistry Jeronimo Matos, Handan Yildirim, Abdelkader Kara The characteristics of Benzene adsorption on metals and their alloy surfaces, and the interface features have been the subject of many experimental and theoretical studies. With the availability of the new vdW functionals, we revisit this organic molecule/metal system to assess the influence of vdW interactions on the adsorption as well as to examine the performance of these vdW functionals. We will present the adsorption geometries, adsorption energies and heights, the characteristics of interface electronic structure, and the charge transfer for Benzene adsorption on the (110) surfaces of seven transition metals; Au, Ag, Cu, Pd, Pt, Rh, and Ni. The calculations are carried out using PBE and vdW-DF family functionals implemented in the VASP package. We will provide comparisons with the available experimental and theoretical studies on the adsorption geometries and energies, and the effect introduced by varying surface chemistries. We will also provide comparisons with the recent study for Benzene adsorption on the (111) surfaces of the same metal substrates$^{\mathrm{\thinspace }}$[1]. [1] H. Yildirim, T. Greber, and A. Kara J. Phys. Chem. C 2013, 117, 20572. [Preview Abstract] |
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H1.00210: AFM Nanolithography of Lanthanum Barium Manganese Oxide (LaBaMnO$_{3}$)Thin Films: The Effect of Oxygen Pressure Variations During Film Growth Christopher Stumpf, David Schaefer, Rajeswari Kolagani, Grace Yong, Zoey Warecki In AFM nanolithography, a bias voltage applied between the tip of an atomic force microscope (AFM) and a sample is used to produce nanoscale modifications of material surfaces. AFM nanolithography has been studied extensively on a variety of materials, but limited studies have been performed on perovskite manganites such as Lanthanum Barium Manganese Oxide (LBMO). Studying such materials is important because of their potential applications for room-temperature nanoscale spintronic devices. Previous research on LBMO by our group has focused on how parameters such as applied tip voltage, temperature, and humidity affect the creation of nanopatterns. This paper reports on the influence of growth pressure of the LBMO films grown by pulsed laser deposition. Films grown on (100) SrTiO$_{3}$ were studied for growth pressures ranging between 100 mTorr to 400 mTorr. Our studies indicate that the type of nanopatterns induced by AFM and the relaxation dynamics of these patterns are sensitive to the film growth pressure. The growth pressure is mainly known to affect the oxygen concentration and the surface roughness, but possible variations in cationic stoichiometry could also contribute to these results. [Preview Abstract] |
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H1.00211: Mechanical Loss Measurements of Coated Substrates for Gravitational Wave Interferometry Thaddeus Baringer, Gregory Harry, Jonathan Newport, Hannah Fair, Alexandra France Gravitational waves from sources such as binary star systems, supernovae explosions and stochastic background radiation have yet to be directly detected by experimental observations. Alongside international collaborators, the Laser Interferometer Gravitational-Wave Observatory (LIGO) is designed to realize direct detection of gravitational waves using interferometric techniques. The second generation of gravitational wave observatories, known as Advanced LIGO, are currently undergoing installation and commissioning at sites in Hanford, Washington and Livingston, Louisiana. The ultimate sensitivity of Advanced LIGO within select spectral bands is limited by thermal noise in both the high-reflective coatings and epoxies of the interferometer optics. The LIGO lab at American University is measuring the mechanical loss of coated substrates to predict thermal noise within these spectral bands. These predictions are used to ensure the ultimate design sensitivity of Advanced LIGO and to study coating and substrate materials for future gravitational wave detectors. [Preview Abstract] |
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H1.00212: Structural, optical and electronic properties of Co-doped ZnO films synthesized by plasma deposition Zhaofeng Wu, Feng Zhang Zn$_{\mathrm{1-x}}$Co$_{x}$O films were prepared by plasma deposition method. The wurtzite ZnO crystal can be well retained up to a Co composition of 9.5{\%} and doped Co ions substituted into Zn sites of ZnO host lattice. All the samples show high transparency over the wavelengths from 400 to 1000 nm. There are three absorption bands located on 567, 615, and 659 nm in the optical transmittance spectra for Co doped ZnO films, which correspond to the electronic transition of Co 3d orbitals in the oxygen tetrahedron, showing the incorporation of Co into the Zn sites in the wurtzite ZnO host lattice. Photoluminescence (PL) spectra show UV emission at $\sim$3.45 eV shifts to higher energy side with Co doping, indicating the possibility of band-gap engineering in Zn$_{\mathrm{1-x}}$Co$_{x}$O films. By sputtering Ag islands onto Co doped ZnO films, large enhancement in the band gap emission intensity was observed by coupling through localized surface plasmons. These results indicate that the films synthesized in our experiment may be applied to manufacture of high efficiency ultra violet light emitting devices. [Preview Abstract] |
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H1.00213: An alternative approach to the determination of the local density of states of a conducting sample Chris Hellenthal, Stefan Kooij, Harold Zandvliet Traditionally, open-loop scanning tunnelling spectroscopy (STS) has been used to determine the local density of states (LDOS) of conductive samples in order to obtain information about their electronic structure. Here, we present an alternative scheme to determine the LDOS of a conducting sample via STS measurements. Through the use of a numerical fitting algorithm, the LDOS can be reconstructed from either a measured tunnelling current or a measured tip-sample distance as a function of the applied bias voltage between tip and sample. The requisite measurements can be performed in open-loop or closed-loop configuration, making it a versatile and widely accessible method. [Preview Abstract] |
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H1.00214: Molecular electronics: the single-molecule switch and transistor Kai Sotthewes, Victor Geskin, Rene Heimbuch, Avijit Kumar, Harold Zandvliet In order to design and realize single-molecule devices it is essential to have a good understanding of the properties of an individual molecule. For electronic applications, the most important property of a molecule is its conductance. Here we show how a single octanethiol molecule can be connected to macroscopic leads and how the transport properties of the molecule can be measured. Based on this knowledge, we have realized two single-molecule devices: a molecular switch and a molecular transistor. The switch can be opened and closed at will by carefully adjusting the separation between the electrical contacts and the voltage drop across the contacts. This single-molecular switch operates in a broad temperature range from cryogenic temperatures all the way up to room temperature. Via mechanical gating, i.e. compressing or stretching of the octanethiol molecule, by varying the contact's interspace, we are able to systematically adjust the conductance of the electrode-octanethiol-electrode junction. This two-terminal single-molecule transistor is very robust, but the amplification factor is rather limited. [Preview Abstract] |
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H1.00215: Novel spin propertries of non-Rashba-type surface states with low symmetries Kokin Nakajin, Shuichi Murakami Surface states in Tl/Si(111)-(1$\times$1) and $\beta$-Bi/Si(111)-($\sqrt{3}\times \sqrt{3}$) show non-Rashba-type spin splitting due to spin-orbit interaction. We construct effective tight-binding models on the triangular lattice for the surface states of Bi/Si and Tl/Si crystals with spin-orbit interaction, respecting the crystal symmetries. Consequently, our two results qualitatively agree with the experimental results. We find a new term in the Tl/Si model, which does not exist in Rashba systems. In addition, we apply the theory of persistent spin helix in semiconductors for the Tl/Si crystal because there are two nested hole pockets with opposite spin directions when doping holes to this crystal. As a result, we find spin helix states on the surface with a long spin life time. Furthermore, we numerically study the bound states at the junction between the two surface regions which have different signs of the spin-orbit interaction parameters in the Bi/Si system and in the Tl/Si system. As a result, we find bound states in these systems. [Preview Abstract] |
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H1.00216: An extensive computational study of the adsorption of thiophene on transition metal surfaces: role of van der Waals Tomas Rojas, Abdelkader Kara Van der Waals (vdWs) interactions play a significant role in the determination of the adsorption characteristics at the interface between a molecule and a substrate. In this study,~self-consistent inclusion of vdW interactions in density functional theory~provides a good perspective to understand the interaction between organic adsorbates and inorganic interfaces. We present the results of adsorption of thiophene (C$_{\mathrm{4}}$H$_{\mathrm{4}}$S) on various~transition metal surfaces with the goal of comparing the performance of five different vdW functionals (optB86, optB88, optPBE, revPBE, rPW86). ~Seven metallic substrates (100) are used for our study; three coinage metals (Au, Ag, Cu) and four reactive metals (Pt, Pd, Rh, Ni). The results show that vdWs inclusion enhances the interaction for Ag ( 0.08 to 0.73 eV), Au (0.14 to 0.86 eV), Cu (0.12 eV to 0.77 eV), Ni(1.56 to 2.34 eV), ~Pt (1.6 to 2.51 eV), Pd (1.67 to 2.54), Rh (1.74 to ~2.96 eV). In addition, we performed calculations for adsorption heights along with analysis of the electronic changes (charge transfer, changes in the d-band of the substrate, and change in the work function) to complement our understanding of these systems. [Preview Abstract] |
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H1.00217: Probing electronic state at atomic scale on the surface of SrVO3 film Yoshinori Okada, Ryota Shimizu, Susumu Shiraki, Taro Hitosugi Probing electronic structure of atomically well controlled surface of Perovskite-type 3d transition-metal oxides have been attracting much interest because of their intriguing emergent physical properties by heterostructure engineering. In this study, we have especially focused on SrVO3, where importance of correlation effects has been considered. We successfully obtained atomically flat surfaces of SrVO3, which gave us the great opportunity to visualize correlated electronic state at atomic scale by means of spectroscopic imaging scanning tunneling spectroscopy. Based on the experimental data, we discuss spectroscopic signature of many body effects on the surface of SrVO$_{\mathrm{3}}$ system. [Preview Abstract] |
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H1.00218: Hard X-ray Photoelectron Spectroscopy Investigation of Off-Stoichiometric LaAlO3 interfaces with SrTiO$_{3}$ Conan Weiland, George E. Sterbinsky, Abdul K. Rumaiz, Joseph C. Woicik, C. Stephen Hellberg, Shaobo Zhu, Darrel G. Schlom LaAlO$_{3}$ (LAO) and SrTiO$_{3}$ (STO) are both insulators, yet the interface between TiO$_{2}$-terminated STO and LAO is a high mobility conductor when the LAO film is above a critical thickness. The origin of this conductivity is under debate; possible explanations for conductive interfaces include chemical intermixing, oxygen defects, and charge redistribution arising from the built-in potential due to the polar LAO layers on the non-polar STO surface. Recently, interfacial conductivity has been found to depend on the stoichiometry of the LAO film, with Al-rich samples providing conductive interfaces, while stoichiometric and La-rich samples do not. Here, hard x-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy XPS (VKE-XPS) have been used to investigate the interface of 10 unit cell films of La-rich, Al-rich, and stoichiometric LAO on STO. [Preview Abstract] |
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H1.00219: METALS AND METALLIC ALLOYS |
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H1.00220: Crystal structure and ferromagnetism of the new Gd$_{3}$(Co$_{x}$Ni$_{1-x})_{2}$ compounds Alessia Provino, Pietro Manfrinetti, Marina Putti, Durga Paudyal, Karl A. Gschneidner Jr. The rare-earth binary compound ``Gd$_{3}$Ni$_{2}$,'' reported in current literature with an uncertain composition and unknown crystal structure, has been synthesized. We have found it to be a high temperature and stoichiometric phase; it exists in the range between 660-695 $^{\circ}$C and can be retained at room temperature, as a metastable phase, by mild quenching. Its crystal structure has been studied: it crystallizes in the monoclinic Dy$_{3}$Ni$_{2}$ structure type [\textit{mC}20, space group $C$2/$m$, Z$=$4, the lattice parameters are $a=$13.418(3) {\AA}, $b=$3.720(1) {\AA}, $c=$9.640(2) {\AA}, $\beta =$106.250(3) $^{\circ}$]. It has also been found that Ni can be replaced by substituting Co: up to x $\approx $ 1 without change of the crystal structure . Moreover, such substitution appears to stabilize these new phases down to room temperature. The physical properties of all these phases have been investigated. Gd$_{3}$Ni$_{2}$ shows a ferromagnetic behavior with T$_{C}=$150 K; the transition temperature increases with the Co content. The magnetocaloric properties have also been studied by magnetization and heat capacity measurements. Theoretical calculations have been performed to explain the phase stability, formation, and the ferromagnetic behavior of these compounds. [Preview Abstract] |
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H1.00221: Structural, Magnetic, and Microstructural Properties of Rapidly Solidified Ni$_{54}$Fe$_{21}$Ga$_{25-x}$Al$_{x}$ Ribbons Imaddin Al-Omari, S. Aich, K. Kumar Polycrystalline rapidly solidified Ni$_{54}$Fe$_{21}$Ga$_{25-x}$Al$_{x}$ ribbons (x$=$0, 1, 2, 3, 4) were prepared by arc-melting followed by vacuum melt spinning. The microstructures and phase formations of the cast alloys and ribbons were investigated by X-ray diffraction, scanning electron microscope, and transmission electron microscope. These studies indicated that upon rapid solidification processing the occurrence of $\gamma $-phase is suppressed leading to the formation of a structure consisting of only L2$_{1}$ ordered phase, while after annealing the $\gamma $-phase can be reappeared. The changes in various phase transformation temperatures were investigated by differential scanning calorimeter and found that there is a decrease in the glass transition temperature and in delta C$_{p}$ with increasing the Al concentration. The magnetic behaviors of these ribbons were studied using a vibrating sample magnetometer and found that all the samples under investigation were ferromagnetic in nature. The magnetization at room temperature and at an applied magnetic field of 13.5 kOe was found to decrease with increasing the Al percentage. [Preview Abstract] |
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H1.00222: MATTER AT EXTREME CONDITIONS |
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H1.00223: Evaluating the Thermal Damage Resistance of Reduced Graphene Oxide/Carbon Nanotube Hybrid Coatings Lamuel David, Ari Feldman, Elisabeth Mansfield, John Lehman, Gurpreet Singh Carbon nanotubes and graphene are known to exhibit some exceptional thermal (K $\sim$ 2000 to 4400 W.m$^{-1}$K$^{-1}$ at 300K) and optical properties. Here, we demonstrate preparation and testing of multiwalled carbon nanotubes and chemically modified graphene-composite spray coatings for use on thermal detectors for high-power lasers. The synthesized nanocomposite material was tested by preparing spray coatings on aluminum test coupons used as a representation of the thermal detector's surface. These coatings were then exposed to increasing laser powers and extended exposure times to quantify their damage threshold and optical absorbance. The graphene/carbon nanotube (prepared at varying mass{\%} of graphene in CNTs) coatings demonstrated significantly higher damage threshold values at 2.5 kW laser power (10.6 $\mu$m wavelength) than carbon paint or MWCNTs alone. Electron microscopy and Raman spectroscopy of irradiated specimens showed that the composite coating endured high laser-power densities (up to 2 kW.cm$^{-2}$) without significant visual damage. [Preview Abstract] |
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H1.00224: Study of the links between surface perturbation parameters and shock-induced mass ejection Shabnam Monfared, William Buttler, LaLone Brandon, David Oro, Cora Pack, Martin Schauer, Gerald Stevens, Joseph Stone Los Alamos National Laboratory is actively engaged in the study of material failure physics to support development of the hydrodynamic models. Our supporting experiments focus on the failure mechanisms of explosively shocked metals that causes mass ejection from the backside of a shocked surface with perturbations. Ejecta models are in development for this situation. Our past work has clearly shown that the total ejected mass and mass-velocity distribution sensitively links to the wavelength and amplitude of these perturbations. In our most recent efforts, we studied the link between amount of tin ejecta and surface perturbation parameters. Our ejecta measurements utilized soft x-radiography and piezoelectric pins to quantitatively determine the amount of ejected mass. Results from these analysis techniques were in remarkably good agreement. In addition, optical shadowgraphy and laser Doppler velocimetry were used to identify any symmetry imperfections as well as fast ejecta and free surface velocities. We also compared our recent results with some earlier measurements. Within each set, amount of ejecta is predictable based on surface parameters. We relate minor differences between the results of our previous and current experiments partially to different surface cuts used. [Preview Abstract] |
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H1.00225: Orientation-dependent response for Tantalum single crystals with dislocation sources Eduardo Bringa, Diego Tramontina Defective Tantalum single crystals are expected to display a particularly rich behavior when subjected to shock waves. Using non-equilibrium molecular dynamics simulations, we model Ta single crystals containing pre existing defects, which acts as sources for heterogeneous nucleation of defects, including point defects, dislocations and twins. We use a recent embedded atom model interatomic potential specially suited for high pressure simulations [Ravelo et al., Phys. Rev B, (2013)]. Differences on the Hugoniot Elastic (HEL), dislocation densities and twin fractions for shocking along several crystalline directions have been found, resulting in a variety of microstructures [Tramontina et al., High Energy Density Physics, (2014)]. Increasing the rise time of the loading ramp typically decreases dislocation densities. Survival of defects after unloading and Taylor-wave loading lead to a significant decrease in the final dislocation densities and twin fractions, giving results comparable to recent recovery experiments. [Preview Abstract] |
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H1.00226: Quantum mechanical modeling of hydrogen assisted cracking in aluminum Qing Peng, Yi Sun, Gang Lu We report multiscale quantum mechanical modeling of hydrogen assisted cracking in aluminum which is central to H embrittlement phenomena. We find that dislocation emission and brittle cleavage can occur simultaneously. H embrittlement takes place when H occupies the top sites on the crack front surface and even a very low H coverage at 0.2 monolayers can lead to brittle cleavage. H atoms adsorbed on the crack surfaces tend to suppress dislocation emission, whereas the solute H atoms on the slip plane can promote dislocation emission. Top-site H atoms at the front surface are found to facilitate the migration of other H atoms towards the front surface, providing a mechanism for H accumulation at the crack tip. The study resolves a long-standing puzzle of why H embrittlement could occur in Al where the equilibrium H solubility is extremely low under normal conditions. [Preview Abstract] |
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H1.00227: The Sun on Trial Pierre-Marie Robitaille For 150 years, the Sun has been seen as a gaseous object devoid of a surface, as required by the Standard Solar Model (SSM). Yet, not one line of observational evidence supports a gaseous Sun. In contrast, overwhelming evidence exists that the Sun is comprised of condensed matter. Recently, 40 proofs have been compiled in conjunction with the Liquid Metallic Hydrogen Solar Model (LMHSM). This model advances that the Sun has a true surface. Photospheric structures, such as sunspots, granules, and faculae, are not optical illusions, as in the SSM, but real objects with a condensed nature. The LMHSM accounts for the thermal spectrum by invoking true inter-atomic structure on the photosphere in the form of the graphite-like layered hexagonal metallic hydrogen lattice first proposed by Wigner and Huntington. Within the convection zone, layered metallic hydrogen, insulated by intercalate atoms, enables the generation of the solar dynamo. Electrons located in conduction bands provide a proper means of generating magnetic fields. Metallic hydrogen ejected from the photosphere also thinly populates the corona, as reflected by the continuous K-coronal spectrum. This coronal matter harvests electrons, resulting in the production of highly ionized atoms. Electron affinity, not temperature, governs the ion profile. The chromosphere is a site of hydrogen and proton capture. Line emission in this region, strongly supports the idea that exothermic condensation reactions are occurring in the chromosphere. In the LMHSM, solar activity and solar winds are regulated by exfoliation reactions occurring in the Sun itself, as the metallic hydrogen lattice excludes non-hydrogen elements from the solar body. [Preview Abstract] |
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H1.00228: MAGNETISM |
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H1.00229: Studying the Magnetic Resonance properties of Superparamagnetic Iron Oxide (Fe$_{2}$O$_{3})$ Nanoparticles So Jin Park, Behrouz Khodadadi, Thomas Macher, Tim Mewes, Yuping Bao Ferromagnetic Resonance (FMR), which measures the resonance field by detecting the precessional motion in response to a microwave field, is used to analyze the effects of the polymer matrix concentration of polyacrylic acid (PAA) and presence of bias field on the magnetic properties of citrate coated iron oxide nanoparticles. The nanoparticles were dispersed into three different levels of PAA concentration: citrate coated iron oxide nanoparticles in water (0 mg PAA matrix), nanoparticles in low PAA (1mg), and high PAA (5mg) matrix. The polymer matrix aided in fixing the nanoparticles into place, which restricted mechanical movement. In addition, a bias field created by two permanent magnets was used to harden samples of nanoparticles with PAA while subject to a magnetic field. Our results indicated that nanoparticles in solution (not fixed) had the overall highest linewidth compared to the nanoparticles dispersed in polymer matrix, in both samples with and without a bias field. The larger linewidth could be due to the large inhomogenity in the dipole-dipole interaction found in the freely moving nanoparticles. It was also observed that the arrangement of the bias field relative to the external field during measurements had an effect on the magnetic properties. [Preview Abstract] |
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H1.00230: Band structure of a 2D photonic crystal based on ferrofluids of Co$_{\mathrm{(1-x)}}$Zn$_{\mathrm{x}}$Fe$_{2}$O$_{4}$ nanoparticles under perpendicular applied magnetic field Javier Lopez, Luz Esther Gonzalez, Mario Quinonez, Nelson Porras, Gustavo Zambrano, Maria Elena Gomez Using a ferrfluid of cobalt-zinc ferrite nanoparticles Co$_{\mathrm{(1-x)}}$Zn$_{\mathrm{x}}$Fe$_{2}$O$_{4}$ coated with oleic acid and suspended in ethanol, we have fabricated a 2D photonic crystal (PC) by the application of an external magnetic field perpendicular to the plane of the ferrofluid. The 2D PC is made by rods of nanoparticles organized in a hexagonal structure. By means of the plane-wave expansion method, we study its photonic band structure (PBS) which depends on the effective permittivity and on the area ratio of the liquid phase. Additionaly, taking into account the Maxwell-Garnett theory we calculated the effective permittivity of the rods. We have found that the effective refractive index of the ferrofluid increases with its magnetization. Using these results we calculate the band structure of the photonic crystal at different applied magnetic fields, finding that the increase of the applied magnetic field shifts the band structure to lower frequencies with the appearance of more band gaps. This work has been supported by the ``El Patrimonio Autonomo Fondo Nacional de Financiamiento para CTI FJC'' Colciencias-CENM Research Projects: No. 1106-48-925531 and CI7917-CC 10510 contract 0002-2013 COLCIENCIAS-UNIVALLE. [Preview Abstract] |
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H1.00231: Mossbauer investigation of iridium oxide-hematite nanoparticles Julia Limongelli, Monica Sorescu Iridium oxide-doped hematite, xIrO$_{2}$*(1-x)$\alpha$-Fe$_{2}$O$_{3}$ with concentration x=0.1, 0.3, and 0.5, were prepared using ball milling with samples taken at times 0, 2, 4, 8, and 12 hours. The resulting M\"ossbauer spectra of the nanoparticles systems were parameterized using NORMOS-90. For each concentration, the spectra for 0 hours consisted of one sextet because the substitution of IrO$_{2}$ into Fe$_{2}$O$_{3}$ did not appear until 2 hours ball milling time (BMT). For x=0.1 and 0.3 and BMT 2 hours, the spectra were fit with three sextets. The remaining spectra in x=0.1 and 0.3 were each fit with four sextets. For concentration x=0.5, each spectra from BMT 2-12 hours was fit with four sextets and one quadrupole-split doublet. With increasing initial concentration, the appearance of the quadrupole-split doublet also increased, indicating that the reverse substitution of Fe into IrO$_{2}$ also occurred. Increased BMT did not influence the profusion of quadrupole-split doublets, however it did affect the number of sextets; as the BMT increased per concentration, the number of sextets also increased. This shows that increasing the initial concentration causes an increase in the amount of IrO$_{2}$ that is substituted into Fe$_{2}$O$_{3}$. [Preview Abstract] |
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H1.00232: A M\"{o}ssbauer study of ruthenium oxide-hematite nanostructures Christopher Stroh, Monica Sorescu Ruthenium oxide-doped hematite, xRuO$_{2}$(1-x)$\alpha$-Fe$_{2}$O$_{3}$ (x = 0.1 - 0.7) solid solutions were synthesized using ball milling. Samples were taken at 0, 2, 4, 8, and 12 hours ball milling time (BMT). NORMOS-90 software was utilized to identify parameters for the M\"{o}ssbauer spectra of the samples using least-squares fitting. At 0 hours BMT, all concentrations displayed only one sextet. As the BMT increased, the sample of x = 0.1 displayed two sextets at 2 hours, and three sextets for all subsequent times. This correlates well with the substitution of Ru for Fe in the hematite lattice. In increased concentrations, quadrupole-split doublets appeared and the number of sextets increased with BMT. As the BMT increased, the abundance of the quadrupole split doublets increased as well, indicating that the replacement of Ru$^{4+}$ with Fe$^{3+}$ increased in the RuO$_{2}$ lattice. The most apparent example of this is in the x = 0.7 sample, at 2 hours BMT the abundance of the doublet is 5.251\%, however at 12 hours BMT the abundance reaches 52.678\%. The quadrupole-split doublets also increased in abundance as the concentration of the sample was increased. The findings of this research show the reality of creating nanoparticle solid solutions by mechanical means. [Preview Abstract] |
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H1.00233: Chemically synthesized FePt nanoclusters Victor Velasco, Frank Abel, XiaoCao Hu, Patricia Crespo, George Hadjipanayis FePt nanoparticles (NPs) are being widely investigated due to their high potential applications in magnetic recording media and biomedicine. These NPs are expected to be ideal candidates due to their excellent magnetic properties, such as high K and high Ms together with a high chemical stability. In this work, the FePt NPs have been synthesized by chemical routes according to the method reported by M. Chen \textit{et al}.\footnote{M. Chen. J. P. Liu and S. Sun, J. Am. Chem. Soc. 2004, 126, 8394-8395.} At high temperature, surfactants together with iron pentacarbonyl are added to the solution and thermally decomposed. By controlling the injection temperature and the heating rate, we have been able to obtain homogeneous spherical clusters with an average size of 38 $\pm$ 10 nm formed by 5 nm-FePt NPs. These clusters are found to be superparamagnetic above Tb of 55 K whereas at 5 K exhibit a coercive field of 1.2 kOe. Furthermore, these NPs seem to be highly stable in water after replacing the surfactants by TMAOH. These clusters appear to be good candidates for MRI and hyperthermia applications. [Preview Abstract] |
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H1.00234: Plasmon-mediated large enhancement of magneto-optical activity in colloidal magnetic metals Gervasi Herranz, Ondrej Vlasin, Oana Pascu, Anna Roig Magnetic properties may undergo dramatic changes at the nanoscale that, eventually, can be exploited as a basis for enhanced functionality. This is the case that we present here, in which we analyzed the rotation and ellipticity that magnetic nanoparticles exerted on the polarization of light. More specifically, we observed an outstanding increase of the magneto-optical activity at the frequencies of the plasmon resonances of the metallic magnetic nanoparticles, yielding a dramatic increase of the Verdet constant. Furthermore, we have established an innovative theoretical framework in excellent quantitative agreement with the experimental data, endowing our model with a powerful predictive character for the interaction of polarized light with magnetic nanoclusters embedded in dielectric hosts. The relevance of our results goes well beyond the particular case of colloidal metals, as other systems such as metal inclusions in polymers or glasses containing small magnetic clusters can be as well considered. In addition, the observed large Verdet constants allow envisioning the exploitation of light polarization, instead as the commonly used reflectance, as a probe for plasmon-sensing devices. Our results provide new routes for plasmon-based biological and chemical detection. [Preview Abstract] |
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H1.00235: Impurity induced enhancement of perpendicular magnetic anisotropy and spin polarization in Fe/MgO magnetic tunnel junctions Ali Hallal, Bernard Dieny, Mairbek Chshiev Magnetic tunnel junctions (MTJ) with perpendicular magnetic anisotropy (PMA) provide better thermal stability and lower switching current compared to in-plane MTJs [1]. In this context, Fe/MgO MTJs have been extensively studied where PMA values of 1-2 mJ/m$^2$ have been reported [1-3]. To maximize the effective PMA in Fe/MgO we propose to lower the saturation magnetization of the magnetic electrodes by introducing non-magnetic impurities X$=$Cr,V in Fe to maintain the PMA for thicker FeX alloys. Using first-principles calculations we investigated the effect of impurities on the magnetic anisotropy in Fe(001)/MgO. To avoid the depolarization of the interfacial Fe layer we calculated the effective PMA as function of impurities concentration by including impurities only in the bulk of Fe. The effective PMA is found to increases as a function of Cr and V concentration with V being more efficient compared to Cr impurities [4]. \\[4pt] [1] S. Ikeda et al, Nature Mater., 9 (2010) 271.\\[0pt] [2] C.-H. Lambert et al, Appl. Phys. Lett. 102, 122410 (2013)\\[0pt] [3] H. X. Yang et al, Phys.Rev. B 84, 054401 (2011); A. Hallal et al, accepted in PRB.\\[0pt] [4] A. Hallal et al, in prep. [Preview Abstract] |
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H1.00236: The consequences of similarity of hysteresis loops for interpreting magnetic particle systems Sergiu Ruta, Ondrej Hovorka, Ryan Booth, Sara Majetich, Roy Chantrell One of the challenges in understanding interacting magnetic particle (MP) assemblies is the interpretation of their physical parameters from magnetization measurements. A common framework has been based on the Langevin function approach, applicable in the super-paramagnetic limit of weakly interacting MPs . If interactions are significant or in case of thermally blocked MPs the issue becomes complicated by the presence of memory effects and hysteresis, and the question of uniqueness of parameter identification arises. To study this question, we consider a kinetic Monte-Carlo model of dipolar interacting Stoner-Wohlfarth MP, including volume and anisotropy distributions. By applying the grid search methods combined with the least squares fitting approach we map the parameter regions of hysteresis loops indistinguishable within a statistical confidence. This allows to show that a unique extraction of model parameters is indeed possible only in a certain range of MP concentrations and temperatures. Thus the hysteresis loop similarity prohibits a reliable parameter identification - being a fundamental issue that may potentially be resolved only by devising different measurements protocols. [Preview Abstract] |
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H1.00237: Synthesis and characterization of Cobalt Telluride Nanotubes Rajendra Dulal, Bishnu Dahal, Keshab Sapkota, Parshu Gyawali, Adrien Lermechin, Ian L. Pegg, John Philip Cobalt telluride nanotubes have been synthesized by means of a wet chemical synthesis. High quality cobalt telluride nanotubes were prepared through a two step process. Initially, tellurium nanowires were synthesized at 160 $^{\circ}$C from TeO$_{3}$ and then cobalt precursor was injected into the solution containing tellurium nanowires at 180 $^{\circ}$C. Cobalt diffusion into tellurium nanowires were not complete if the temperature was maintained below 180 $^{\circ}$C. These CoTe nanotubes exhibit hexagonal crystal structure. They are ferromagnetic at 10 K. [Preview Abstract] |
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H1.00238: Misalignment of ferromagnetic and antiferromagnetic easy axes in exchange-coupled bilayers Roberto Rodriguez, Alexandre Oliveira, Henrry Vega, Sebastian Michea, Antonio Azevedo In this work we studied the exchange bias phenomenon existing at ferromagnetic (FM)/ antiferromagnetic (AF) bilayers, which were fabricated by oblique sputtering deposition. Sputtering deposition induces strong uniaxial anisotropy in ferromagnetic films with its easy axis perpendicular to the plane of incidence. Sputtering deposition of magnetic thin films with a magnetic field applied parallel to the substrate can also produce a high uniaxial anisotropy. Our samples were grown with a magnetic field applied perpendicular to the easy axis created by the oblique deposition. For this reason, we created a competition between both anisotropy mechanisms: sputtering shadowing effects and magnetic field applied during deposition. A misalignment between the FM and AF easy axes was investigated using Magneto Optical Kerr Effect (MOKE) and Ferromagnetic Resonance techniques. In order to interpret MOKE results we used a phenomenological approach, based on Stoner-Wohlfarth model, which takes into account all relevant free energy contributions. Thus, we compared results from two different techniques. By means of our model it was possible to use the theoretical angular dependence of hysteresis loop shift to explain the experimental one. It should be stated that in MOKE measurements we found out hysteresis loops similar to the usual uniaxial anisotropy hard axis, but shifted by a field value. [Preview Abstract] |
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H1.00239: Surface Defects: Possible Source of Room Temperature Ferromagnetism in Co-Doped ZnO Nanorods Altaf Karim, Nadeem Tahir, Yi-De Chuang, Kristin Persson, Tajammul Hussain, Alejandro Cruz, Muhammad Naeem, Muhammad Usman, Zahid Hussain, Ruimin Qiao, Wanli Yang Contradicting results about the origin of room temperature ferromagnetism (RTFM) from measurements on different forms of transition metal (TM)-doped ZnO nanostructured materials lead to strong debates on whether RTFM could be an intrinsic property to TM-doped ZnO or not. Through careful synthesis and extensive characterizations, we have excluded the extrinsic contaminations as the cause of RTFM. Our experimental study confirms that defects such as oxygen vacancies lie on surface of nanorods and are likely a source of RTFM. X-ray absorption and emission spectroscopy (XAS and XES) suggest that the doped Co ions, primarily in the divalent state, replace the Zn ions inside the tetrahedral without introducing Co clustering or Zn-related defects. Furthermore, such a trend can be nicely reproduced in GGA$+$U band structure calculations. Our findings highlight the importance of using the nanocrystalline surfaces to enhance the impurity concentrations and stabilize the ferromagnetism without post-sample annealing in an oxygen-deficient environment. [Preview Abstract] |
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H1.00240: Room-temperature ferromagnetic behavior in electride 12CaO$\cdot $7Al$_{2}$O$_{3}$ Nororu Wada, Sho Nakamura, Kotaro Tsubaki Crystalline dodecacalcium hepta-aluminate 12CaO$\cdot $7Al$_{2}$O$_{3}$ (C12A7) has a nanoporous structure that contains twelve cages with an inner diameter of ~0.44 nm per unit cell. By replacing the O$^{2-}$ ions originally incorporated in some cages with electrons, C12A7 becomes electride and is known to exhibit a variety of interesting physical and chemical properties. Here, we report results on SQUID magnetic measurements of electride C12A7, where ferromagnetic behavior that persisted even above room temperature was found. Electride samples were prepared by heating C12A7 samples in vacuum with metallic Ca at 700 and 800 $^{\circ}$C for specific periods of time. Although as-is C12A7 samples showed paramagnetic behavior, once the as-is samples were reduced with metallic Ca, they exhibited magnetization curves which suggested ferromagnetism. It was found that the longer the reducing time was and the higher the reducing temperature was, the larger the saturation magnetization value became. Systematic magnetization behavior found as functions of reducing time and temperature might suggest the ferromagnetism found in electride C12A7 originated from the electron spins in the cages. The origin of ferromagnetism found in electride C12A7 will be discussed. [Preview Abstract] |
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H1.00241: Fe/MgO/Fe Tunnel Magneto Resistance Structure Alexander Newman, Dereje Seifu Tri-layer thin films of Fe/MgO/Fe were synthesized using magnetron DC/ RF sputtering on MgO(100) at several substrate temperatures. The multi-layered samples thus produced were studied using in-house built magneto-optic Kerr effect (MOKE) instrument, vibrating sample magnetometer (VSM), torque magnetometer (TMM), atomic force microscopy (AFM), magnetic force microscopy (MFM), and magneto resistance (MR) measurements. This system, that is Fe/MgO/Fe on MgO, is a well-known tunnel magneto resistance (TMR) structure often used in magnetic tunnel junction (MTJ) devices. TMR effect is a method by which MTJs are used in developing magneto-resistive random access memory (MRAM), magnetic sensors, and novel logic devices. The main purpose behind this research is to measure the magnetic anisotropy of Fe/ MgO/ Fe structure which is correlated to magneto-resistance property. In this presentation, we will present results on MOKE, VSM, TMM, AFM, MFM, and MR studies of Fe/MgO/Fe on MgO(100). [Preview Abstract] |
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H1.00242: Fe/Bi$_{2}$Te$_{3}$/Fe Tunneling Magneto-Resistance with topological insulator barrier Vallery Salomon, Dereje Seifu Thin film tri-layer structure Fe/Bi$_{2}$Te$_{3}$/Fe was synthesized using magnetron DC / RF sputtering. This sample was synthesized at a substrate temperature of 100 $^{\circ}$C. It was studied using in-house built magneto-optic Kerr effect (MOKE) instrument. The operating principles of MOKE consist of measuring changes in polarization of light reflected from a magnetic sample. The bulk magnetization was measured using vibrating sample magnetometer (VSM) and torque magneto meter (TMM). Topographic structure and magnetic domains were studied using atomic force microscope (AFM) and magnetic force microscope (MFM). Tunnel magneto-resistance (TMR) effect occurs in a structure that is composed of two conductors separated by a thin insulator of the order of few nanometers, the insulator barrier in this case is a well known topological insulator, Bi$_{2}$Te$_{3}$. In this structure, electrons tunnel from one of the conductors to the other through the insulating barrier. This is a forbidden process in classical physics, tunnel magneto-resistance is a purely quantum mechanical effect which is key in developing magneto-resistive random access memory (MRAM), magnetic sensors, and novel logic devices. [Preview Abstract] |
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H1.00243: A New Green Chemical Synthesis Strategy for Synthesis of L10 FePt Nanoparticles from Layered Precursor Fe(H$_{2}$O)$_{6}$PtCl$_{6}$ George Hadjipanayis, Xiaocao Hu, Aldo Capobianchi, Ryan Gallagher In this work, a new green chemical strategy for the synthesis of L1$_{0}$ FePt nanoparticles is reported. The starting material is a polycrystalline molecular complex (Fe(H$_{2}$O)$_{6}$PtCl$_{6})$, in which Fe and Pt atoms are arranged on alternating planes. The starting compound was milled with crystalline NaCl and then annealed under forming gas (5 {\%} H$_{2}$ and 95 {\%} Ar) at 450 $^{\circ}$C for 2h. Finally, the mixture was washed with water to remove the NaCl and L1$_{0}$ FePt nanoparticles were obtained. Transmission electron microscopy (TEM) images revealed that this method is able to produce L1$_{0}$ nanoparticles with different average size varying from 13.9 nm to 5.4 nm depending on the (Fe(H$_{2}$O)$_{6}$PtCl$_{6})$/NaCl ratio. With smaller (Fe(H$_{2}$O)$_{6}$PtCl$_{6})$/NaCl ratio(10mg/20g) and longer milling time(15h), FePt nanoparticles had a smaller size and narrower size distribution. The X-Ray Diffraction (XRD) pattern showed the presence of the characteristic peaks of the fct phase. The hysteresis loop, measured both at room temperature and 50 K, shows a high coercivity of 7.6 kOe and 11.2 kOe, respectively as expected for the high anisotropy L1$_{0}$ phase. Larger precursor/NaCl ratio and shorter ball milling time led to larger coercivity. [Preview Abstract] |
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H1.00244: The Magnetic Properties of Zigzag Boron Carbon Carbon Nitride Nanoribbon J. Rufinus Recently, substantial theoretical and experimental efforts have been made in the quest to find the candidates for future spintronic devices. Two-dimensional graphene-based structures have attracted much attention in the search for new spintronic materials due to some theoretical predictions that this type of materials show the half-metallic property. Here we present the results of an ab-initio self consistent density functional theory within a generalized gradient approximation of zigzag Boron Carbon Carbon Nitride Nanoribbon (ZBC2NNR). The result of our calculations shows different magnetic orderings. In general, however, we found that narrow ZBC2NNR prefers a magnetic state which depends on the shape and the orientation of the atoms on its edges. [Preview Abstract] |
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H1.00245: Micromagnetic Modes in Magnetoelectric Thin Films Ralph Skomski, Priyanka Manchanda, Pankaj Kumar, H. Fangohr, D.J. Sellmyer, Arti Kashyap The effect of an electric field on the anisotropy and coercivity of magnetic thin films investigated theoretically. We use numerical methods, including VASP and micromagnetic simulations, and model calculations to determine both intrinsic and extrinsic properties of metallic thin films. Emphasis is on homogeneneous thin flms and inversion-symmetric trilayers consisting of fcc Co, Pd, and Pt. The electric field redistributes electron states near the Fermi level, which has a fairly strong effect on the surface anisotropy. However, due to the inversion symmetry, the lowest-order net anisotropy of the films remains unchanged. By contrast, the electric field causes the micromagnetic nucleation mode to become spacially asymmetric, which leads to a reduction of the the nucleation field (coercivity) and --- for suitably chosen nanostructures --- to drastic changes in the hysteretic behavior. This nontrivial feature can potentially be exploited in magnetoelectric swuitching devices. [Preview Abstract] |
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H1.00246: Structural, magnetic, transport and dielectric properties of Lu, Y substituted nickel ferrite Ugendar Kodam, Markandeyulu Garimalla Structural, magnetic and transport properties of Lutetium (Lu) and Yittrium (Y) substituted Nickel ferrite (NFO) NiFe$_{1.925}$R$_{0.075}$O$_{4}$(R$=$Lu, Y) were investigated. The samples were prepared by the solid-state reaction method. The materials formed in the cubic inverse spinel phase with small amounts of RFeO$_{3}$ as secondary phases. The back scattered electron imaging confirms both phase. A small rhombohedral distortion of the cubic lattice was observed upon the substitution of Fe by R in the B site. Substitution of Lu and Y for Fe decreased saturation magnetization compared with pure NFO but no change in Curie temperature in contrast to reported. The saturation magnetostriction is seen not to change significantly by the substitution of Lu and Y. Electrical conductivity curves shows the semicoducting magnetic oxide nature. Analysis of the temperature-dependent conductivity indicates that the small polaron and variable-range-hopping mechanisms are operative in the 250-300 and 200-100 K temperature regions, respectively. The dielectric constant of the materials were decreased from that of the pure NFO. Frequency variation of the dielectric constant at room temperature shows a dispersion that could be modeled using modified Debye function which considers the more than one ion contributing to the relaxation. [Preview Abstract] |
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H1.00247: The bilayer ruthenate Sr$_{3}$Ru$_{2}$O$_{6}$ an hypothetical electrically anisotropic compound Pablo de la Mora, Sabina Ruiz-Chavarria, Juan Ramirez, Oliver Martinez, Gustavo Tavizon The bilayer ruthenate Sr$_{3}$Ru$_{2}$O$_{7}$ depending on its preparation it can be ferromagnetic or paramagnetic. In this study the hypothetical compound; Sr$_{3}$Ru$_{2}$O$_{6}$ is studied with quantum-mechanical calculations using the WIEN2k package. This compound is obtained from Sr$_{3}$Ru$_{2}$O$_{7}$ by removing an oxygen atom, then the unit cell is relaxed both in its internal atom positions and the cell dimensions. Before relaxation Sr$_{3}$Ru$_{2}$O$_{6}$ is weakly ferromagnetic, while after relaxation it becomes strongly antiferromagnetic. The parent compound, Sr$_{3}$Ru$_{2}$O$_{7}$, is electrically anisotropic, conducting mainly in the ab plane and Sr$_{3}$Ru$_{2}$O$_{6}$ is much more anisotropic. The electronic structure and magnetic calculations will be presented [Preview Abstract] |
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H1.00248: Multiferroic behavior on nanometric La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ / BaTiO$_{3}$ bilayers Pedro Prieto, John Edward Ordo\~nez, Maria Elena Gomez, Wilson Lopera We have deposited bilayers of the FM La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ and FE BaTiO$_{3}$ as a route to design systems with artificial magnetoelectric coupling on LCMO/BTO/Nb:STO system. We maintain a fixed magnetic layer thickness (t$_{\mathrm{LCMO}} =$ 48 nm) and varying the thickness of the ferroelectric layer (t$_{\mathrm{BTO}} =$ 20, 50, 100 nm). We analyze the influence of the thickness ratio (t$_{\mathrm{BTO}}$/ t$_{\mathrm{LCMO}})$ in electrical and magnetic properties of manganite. From X-ray diffraction analysis we observed that the samples grew textured. Magnetization and transport measurements indicate a possible multiferroic behavior in the bilayer. We found an increase in the Curie and metal-insulator transition temperature in the bilayer in comparison with those for LCMO (48nm)/STO. Hysteresis loops on bilayers show ferromagnetic behavior. This work has been supported by the ``El Patrimonio Aut\'{o}nomo Fondo Nacional de Financiamiento para CT{\&}I FJC'' Colciencias-CENM Research Projects: No. 1106-48-925531 and CI7917-CC 10510 contract 0002-2013 COLCIENCIAS-UNIVALLE. [Preview Abstract] |
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H1.00249: Interface magnetism of two functional epitaxial ferromagnetic oxides integrated with Si (100) Srinivasa Rao Singamaneni, J.T Prater, Fan Wu, J. Narayan Here, we report on the interface magnetic coupling of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrRuO$_{3}$ (LSMO/SRO) bilayer integrated with the technologically important substrate Si (100). We have taken a new approach\footnote{Narayan \textit{et al} J. Appl. Phys$.$ \textbf{93}, 278 (2003).} with which LSMO/SRO bilayer has been epitaxially integrated with Si(100). Magnetization data\footnote{S. S. Rao \textit{et al} under preparation (2013).} collected as a function of biasing layer (SRO) and biased layer (LSMO) thicknesses reveal astonishing evolution of magnetic characteristics. Notable observations include: tunable coercive field (6334-489Oe), exceptional magnetization reversal, intrinsic positive exchange bias, crossover from ferromagnetic to anti-ferromagnetic interface exchange coupling accompanied by additional increase in coercive field as a function of cooling field, double shifted hysteresis loops, and tuning of LSMO Curie temperature. We discuss these emergent physical phenomena in the context of strong interplay among Zeeman, anisotropy and exchange energies. These results have important implications for the physics of exchange biased systems, constitute a significant step in the field of interface magnetism and functional magnetic devices. [Preview Abstract] |
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H1.00250: High Resolution X-ray Diffraction Analysis of Residual Stresses in Epitaxial Thin Films of Rare Earth Manganite Thin Films on Silicon Grace Yong, Kevin Tanyi, Prakash Sharma, Zoey Warecki, Rajeswari Kolagani, Madhana Sunder Epitaxial integration of complex metal oxides on thin films on Si, which is needed for realizing device functionalities, offers challenges on account of several factors such as reactivity of oxide materials with Si at the high temperatures needed for epitaxial growth, the presence/formation of the amorphous native oxide layer, and the thermal expansion mismatch of Si with that of the oxides which leads to the accumulation of stresses during thermal cycling of the film. In order to achieve epitaxial growth circumventing these problems, lattice engineering schemes employing heterostructures of appropriate chemical buffers and structural-templates must be adopted. The film growth parameters and thermal cycling kinetics play a key role in determining the residual stresses in such heterostructures. It is important to monitor the stresses as a function of growth parameters and optimize the parameters to minimize the stresses. We will present our studies of the residual stresses in epitaxial thin films of hole doped rare earth manganite thin films grown on Si using high resolution four-circle x-ray diffraction. [Preview Abstract] |
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H1.00251: Boundary Magnetization and Exchange Bias of Boron Doped Cr$_{2}$O$_{3}$ Pinning Layers Michael Street, Will Echtenkamp, Peter Dowben, Christian Binek This research is part of an effort to utilize voltage-controlled boundary magnetization (BM) in the magnetoelectric (ME) Cr$_{2}$O$_{3}$ for spintronic applications. We exploit the electric switchable boundary magnetic moment (MM) of Cr$_{2}$O$_{3}$. The net MM at the interface can be useful to manipulate the magnetic states of an adjacent ferromagnetic (FM) material. Using a FM Pd/Co multilayer deposited on Cr$_{2}$O$_{3}$, reversible, room-temperature isothermal switching of the exchange bias field has been achieved by reversing the electric field. The voltage-controlled magnetization of the FM layer can be utilized as a state variable. However, to use voltage-controlled BM as a key spintronic material for devices operating at room temperature, the N\'{e}el temperature $T_{N}$ of the ME antiferromagnet must be increased above the bulk value of $T_{N} =$307 K of pure Cr$_{2}$O$_{3}$. First principles calculations show that boron doping of Cr$_{2}$O$_{3}$ can increase $T_{N}$. We diagram structural and magnetic characterizations of pure and B-Cr$_{2}$O$_{3}$ grown on Al$_{2}$O$_{3}$. An increase in $T_{N}$ of 120 K is achieved making Cr$_{2}$O$_{3}$ suitable for room temperature spintronic applications. Further, we attempt to create an exchange bias (EB) system using a FM Pd/Co multilayer on B-doped Cr$_{2}$O$_{3}$. From this, we attempt to switch the EB field via the electric field. [Preview Abstract] |
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H1.00252: Antiferromagnetic Spin Reorientation Transition induced by the coupling at NiO/CoO interface Jie Zhu, Qian Li, Junxue Li, Zhao Ding, Jianhui Liang, Xia Xiao, Yizheng Wu, C.Y. Hua, M.J. Huang, H.-J Lin Manipulating the antiferromagnetic (AFM) spin orientation is important for spitronic researches. But AFM spin-reorientation transition (SRT) can be realized only through limited mechanisms. In this contribution, we realized an in-plane to out-of-plane AFM SRT in NiO/CoO/MgO(001) system through a new mechanism, i.e., the exchange coupling between AFM spins. NiO and CoO spin orientations were determined by X-ray magnetic linear dichroism (XMLD) measurements. The CoO spin was fixed in-plane below Néel temperature (T$_{\mathrm{N}})$, while the NiO spin undergoes an in-plane to out-of-plane SRT above a critical NiO thickness. The SRT is attributed to the competition between NiO out-of-plane anisotropy from expansive strain and in-plane anisotropy from interfacial coupling with CoO spin. The SRT was influenced by CoO AFM ordering modulated by temperature, CoO thickness and interfacial coupling strength tuned by the thickness of MgO layer inserted between NiO and CoO. Besides, temperature-dependent XMLD measurement indicated a rise of CoO T$_{\mathrm{N}}$ by 80K with the proximity effect from NiO. Our experimental results can be further understood by Monte Carlo simulations. [Preview Abstract] |
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H1.00253: Penetration depth and absorption mechanisms of spin currents in Ir$_{80}$Mn$_{20}$ and Fe$_{50}$Mn$_{50}$ polycrystalline films by ferromagnetic resonance and spin pumping Pablo Merodio, Abhijit Ghosh, Christophe Lemonias, Ursula Ebels, Mairbek Chshiev, Helene Bea, Vincent Baltz, William E. Bailey Spintronics relies on the spin dependent transport properties of ferromagnets (F). Although antiferromagnets (AF) are used for their magnetic properties only, some fundamental F-spintronics phenomena like spin transfer torque, domain wall motion and tunnel anisotropic magnetoresistance also occur with AF, thus making AF-spintronics attractive. Here, room temperature penetration depths of spin currents in Ir$_{80}$Mn$_{20}$ and Fe$_{50}$Mn$_{50}$ are determined by F-resonance and spin pumping. We find unlike values in these AF, originating from different absorption mechanisms: dephasing and spin flipping. [Preview Abstract] |
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H1.00254: Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100) Srinivasa Rao Singamaneni, J.T Prater, Fan Wu, S. Nori, D. Kumar, L. Yue, S.-H. Liou, J. Narayan Thorough understanding of epitaxial Ni$_{82.5}$Fe$_{17.5}$ (permalloy, Py) magnetic properties when integrated with the technologically important substrate Si (100) is critical for CMOS-based magnetic devices. Interestingly, we find\footnote{S.S.Rao \textit{et al,} Curr. Opin. Solid State Mater. Sci. (2013), http://dx.doi.org/10.1016/j.cossms.2013.07.004;}$^,$\footnote{S.S.Rao \textit{et al}, under review (2013).} that the magnetic features of Py films in early stages of island coalescence are markedly different from the films formed initially and after extended deposition times. Magnetic data on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations, consistent with the magnetic force microscopy data. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of growth time. [Preview Abstract] |
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H1.00255: Theory of spin Hall magnetoresistance and spin pumping in magnetic trilayers Saburo Takahashi, Takahiro Chiba, Yan-Ting Chen, Gerrit Bauer A theory of spin Hall magnetoresistance (SMR) and spin pumping in a trilayer system made from a metal N sandwiched between two ferromagnetic insulators FI is presented. The SMR, which is induced by the simultaneous action of spin-Hall and inverse spin-Hall effects, is sensitive to the relative orientation of magnetizations of the two FI layers. We demonstrate that SMR in the slightly canted magnetization configuration is greatly enhanced compared with SMR in the parallel configuration. Spin pumping is caused by applying an ac current to the N layer along the direction of parallel magnetizations, thereby generating the out-of-phase precession motion of magnetizations driven by out-of-phase ac magnetic fields. We demonstrate a giant enhancement of spin pumping induced by the out-of-phase precession motion of magnetizations, in which the pumped spin accumulation is greatly enhanced compared to that in the in-phase precession motion. The giant enhancement of spin pumping is discussed in relation to enhanced Gilbert damping. [Preview Abstract] |
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H1.00256: Mode coupling in a two-mode spin-torque oscillator: coexistence, mode-hopping and linewidth broadening Olle Heinonen, Ezio Iacocca, Pranaba Muduli, Johan Akerman Spin-torque oscillators (STOs) are microwave frequency and spin-wave generators with potential technological applications. Single-mode oscillators have been described previously[1]. However, recent experiments have shown STO multi-mode generation [2,3]. By extending the single-mode auto-oscillator theory [1] taking into account mode coupling, we show that single-mode generation, coexistence, and periodic energy transfer are possible to describe analytically. Furthermore, the generation linewidth in a mode-hopping regime exhibits broadening due to the autocorrelation loss, similar to a thermally-driven particle in a double potential well obeying Arrhenius' equation. Our results provide the physical mechanism behind the linewidth broadening at current and temperature driven mode transitions. Argonne National Laboratory is a US DOE Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC. Supported by grants from the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), and the Knut and Alice Wallenberg Foundation. References: [1] Slavin and Tiberkevich, IEEE Trans. Magn. \textbf{45}, 1875 (2009). [2] Muduli et al., Phys. Rev. B \textbf{86}, 174408 (2012); Dumas et al., Phys. Rev. Lett. \textbf{110}, 257202 (2013). [3] Muduli et al., Phys. Rev. Lett. \textbf{108}, 207203 (2012). [Preview Abstract] |
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H1.00257: Transient grating-induced phase inhomogeneity in FeRh studied by time-resolved hard x-ray nanodiffraction Yi Zhu, Qingteng Zhang, Pice Chen, D.A. Walko, E.M. Dufresne, J.U. Thiele, E.E. Fullerton, Zhonghou Cai, P.G. Evans, Haidan Wen The photo-induced antiferromagnetic to ferromagnetic phase transition of FeRh at room temperature has important technological applications in the magnetic recording industry. This first-order phase transition is accompanied by a large, abrupt lattice expansion. In this study, spatially periodic phase modulation in a FeRh thin film was induced by an optical transient grating; the temporal and spatial evolution of the resulting lattice profile was probed by ultrafast hard x-ray nanodiffraction. We found that the transient grating induced lattice profile deviates from the initial sinusoidal spatial modulation during the recovery process, which allows us to quantitatively measure the in-plane propagation of the phase boundary. [Preview Abstract] |
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H1.00258: Exploring magnon-induced spin transfer torques with ultrafast MOKE J. Paul, P. Dey, W. Wendt, P. Jayathilaka, H. Belliveau, C. Miller, D. Karaiskaj We report our efforts to use pump-probe time-resolved magneto-optical Kerr effect (MOKE) to investigate magnon-induced spin torque. A femtosecond laser pulse is used to create magnons that transfer their momentum to the free layer; a probe pulse subsequently probes the spin torque transfer through the device. The samples had the structure Ta (5nm)/ Ni\textunderscore 80Fe\textunderscore 20 (10nm)/ Cu (5nm)/ Ni\textunderscore 80Fe\textunderscore 20 (10nm)/ IrMn (15nm)/ Ta (5nm), and were grown on Si (100) substrates via magnetron sputtering. Using e-beam lithography, nanopillars with dimensions 200 nm by 140 nm were created in an array, which was probed by ultrafast MOKE. [Preview Abstract] |
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H1.00259: Edge spin accumulation in the 2D Rashba system in the quasi-ballistic regime and arbitrary scattering in the bulk Alexander Khaetskii We consider a 2D structure with spin-orbit-related splitting of the electron spectrum described by the Rashba Hamiltonian. We concentrate on the quasi-ballistic case when a mean free path, being much smaller than the sample size, is larger than the spin precession length determined by the value of the spin-orbit splitting. We calculate the edge spin density which arises in the presence of a charge current through the structure for an {\it arbitrary} smoothness of the scattering potential in the bulk. We show that despite the absence of the bulk spin current, the edge spin density appears which character depends on the smoothness of the bulk impurity potential. [Preview Abstract] |
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H1.00260: Growth of Ferromagnetic Epitaxial Film of Hexagonal FeGe on (111) Ge Surface Dushyant Kumar, P.C. Joshi, Z. Hossain, R.C. Budhani The realization of semiconductors showing ferromagnetic order at easily accessible temperatures has been of interest due to their potential use in spintronic devices where long spin life times are of key interest. We have realized the growth of FeGe thin films on Ge (111) wafers using pulsed laser deposition (PLD). The stoichiometric and single phase FeGe target used in PLD chamber has been made by arc melting. A typical $\theta $-2$\theta $ diffraction spectra performed on 40 nm thick FeGe film suggests the stabilization of $\beta $-Ni$_{\mathrm{2}}$In (B8$_{\mathrm{2}}$-type) hexagonal phase with an epitaxial orientation of (0001)FeGe \textbar \textbar (111)Ge and [11-20]FeGe \textbar \textbar [-110]Ge. SEM images shows a granular structure with the formation of very large grains of about 100 to 500 nm in lateral dimension. The magnetization vs. temperature data taken from SQUID reveal the T$_{\mathrm{C}}$ of $\sim$ 270K. Since, PLD technique makes it easier to stabilize the B8$_{\mathrm{2}}$ (Ni$_{\mathrm{2}}$In) hexagonal phase in thin FeGe films, this work opens opportunities to reinvestigate many conflicting results on various properties of the FeGe system. [Preview Abstract] |
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H1.00261: Andreev transport through quantum dots coupled to ferromagnetic and superconducting leads Ireneusz Weymann, Krzysztof Wojcik, Piotr Trocha The local and nonlocal Andreev transport through the system consisting of quantum dot coupled to one superconducting electrode and two ferromagnetic leads is studied theoretically. The magnetizations of the leads are assumed to form either parallel or antiparallel magnetic configuration. To calculate basic transport characteristics, like Andreev current, local and nonlocal conductance, tunneling magnetoresistance, we employ the real-time diagrammatic technique assuming weak tunnel coupling of the dot to ferromagnetic leads. We study the effect of cotunneling processes on Andreev transport in the Coulomb blockade regime. We find a zero-bias anomaly of the Andreev differential conductance in the parallel configuration, which is associated with a nonequilibrium spin accumulation in the dot. We also analyze the linear response transport properties in the case of strong coupling to ferromagnetic leads, when the electronic correlations can lead to the Kondo effect. This transport regime is addressed by means of the numerical renormalization group method. We show that the linear conductance due to Andreev processes strongly depends on the magnitude of exchange field due to the presence of ferromagnetic leads, and the coupling strength to the superconducting lead. [Preview Abstract] |
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H1.00262: Novel Thermodynamics in Dy$_{2}$Ti$_{2}$O$_{7}$ Spin Ice: Two experimental case studies Laura Bovo, Ludovic D.C. Jaubert, Peter C.W. Holdsworth, Steve T. Bramwell Spin-ice systems[1,2] can be described by a network of corner-shared tetrahedra of localised magnetic moments: geometrical spin frustration arises. This problem is topologically equivalent to proton ordering in water ice: to minimise the energy the spins obey the `ice-rule'. Emergent magnetic monopoles[3,4] have been modelled as deconfined excitations carrying a magnetic Coulomb charge which are associated with violations of the ice rule. Spin ices show a variety of properties some of which are better described by spins, other by monopoles. Magnetic susceptibility is a spin property and it shows a peculiar crossover[5]. Here[6] we present a careful experimental observation for spherical crystals. The magnetic entropy[2] is another signature that can be described in terms of magnetic monopoles. Here[7] we show an alternative method based on Maxwell's thermodynamic equations that can yield to the magnetic entropy on an absolute scale. \\[4pt] [1] Harris M.J. et al. PRL 79, 2554(1997) [2] Ramirez A. P.et al. Nature 399, 333(1999) [3] Ryzhkin I.A. J. Exp. and Theor. Phys. 101, 481(2005) [4] Castelnovo C. et al. Nature 451, 42(2008) [5] Jaubert L.D.C. et al. Phys. Rev. X 3, 011014(2013) [6] Bovo L. et al. JPCM 25, 386002(2013) [7] Bovo L.et al. JPCM 25, 356003(2013) [Preview Abstract] |
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H1.00263: Theory of the magnetic properties of the bilayer iridate Sr$_{3}$Ir$_{2}$O$_{7}$ Vera I. Schnells, Henrik M. R\o nnow, Fr\'{e}d\'{e}ric Mila We propose a bilayer pseudospin-1/2 anisotropic Heisenberg model to describe the magnetic properties of the iridate Sr$_{3}$Ir$_{2}$O$_{7}$ at zero temperature using a combination of analytical and numerical methods to explore the excitation spectrum of the system. From x-ray scattering (RIXS) experiments, it is known that the compound's lowest magnetic excitation has a large spin gap of $\sim$92~meV and a bandwidth of $\sim$70~meV. Treating our model using bond-operator mean-field theory, it was possible to reproduce these features accurately. The anisotropy selects an easy $c$-axis collinear antiferromagnetic ground state that has also been observed experimentally. In comparison to other proposed models, we were able to describe both the first and second magnetic excitation branches as transverse and longitudinal triplet excitations. [Preview Abstract] |
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H1.00264: The spin dynamics in perfect and distorted kagome lattices Dirk Wulferding, Peter Lemmens, Young S. Lee, Tianheng Han, Shaoyan Chu, Zenji Hiroi, Hiroyuki Yoshida, Yoshihiko Okamoto When quantum spin systems are restricted in dimensionality and coordination they realize spin liquid states with enhanced quantum fluctuations and exotic correlation functions. We compare the experimentally determined excitation spectra of different spin liquid candidates on a kagome lattice. These include the s$=$1/2 Heisenberg antiferromagnets Herbertsmithite, Vesignieite and Volborthite. Using inelastic light scattering, we are sensitive to probe fractional spinon excitations. The effect of the crystal's lattice structure and defects on the spin dynamics is investigated. The data is also compared with theoretical modelling. [Preview Abstract] |
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H1.00265: Spin oscillation generated by an acoustic wave in single-molecule magnets containing a nanoresonator Gwang-Hee Kim We study the quantum beat of a tunneling spin coupled to a torsional resonator in the presence of an acoustic wave. When the oscillator frequency is large compared to the tunnel splitting, the system displays multiple transitions with macroscopic quantum beat structure during the field sweep. Entanglement of spin and mechanical angular momentum in the presence of a sound wave results in quantum beat as well as abrupt changes of oscillator dynamics, which coincide in time with spin transitions. We show that the size of the transition step in the torsional rotation angle is strongly affected by sound. We compare purely quantum and semiclassical dynamics of the system and discuss their experimental realizations. [Preview Abstract] |
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H1.00266: Electronic transport in Graphene doped with Single Molecule Magnets Sima Saeidi Varnoosfaderani, Adeline Fournet, Annaliese Thuijs, George Christou, Arthur Hebard We report on the interaction of monolayer graphene with Manganese-based single molecule magnets (SMMs) with various ligands. There is a linear relationship between density of states and energy in graphene. So unlike other metals, the density of states is very small near the Fermi energy in graphene and it can be easily modulated via doping. We combine the characterization techniques of Raman spectroscopy and atomic force microscopy with transport measurement to investigate the charge transfer and change in the electronic and magnetic properties of graphene after doping with this first discovered family of SMMs [Mn$_{12}$ O$_{12\, }$(O$_{2}$CR) $_{16}$ (H$_{2}$O) $_{4}$]. Transport measurements show that doping graphene with these magnetic molecules will transfer charge (electrons) from graphene to the molecules and decrease the graphene sheet's resistance and mobility. Magnetoresistance data has been taken to confirm the reduction in the mobility attributed to an increased density of charge impurity scattering centers by doping. [Preview Abstract] |
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H1.00267: Multiplets in single Fe-phthalocyanine molecule on MgO(001) Yukie Kitaoka, Kohji Nakamura, Toru Akiyama, Tomonori Ito, Toyokazu Yamada A challenge to miniaturize devices for novel magnetic application now extends to treating the extreme limit of a single atom or molecule. For molecules with transition-metals (TM), multiplet (or electronic configuration) of the $d$-electrons is an essential aspect in the electronic properties. Further, understandings of molecule-substrate interactions [1] are of crucial importance toward single-molecule-based applications. Previously [2], we demonstrated the utility of the FLAPW method based on the constraint DFT for determining the ground state of the $^{\mathrm{3}}$A$_{\mathrm{2g}}$ electronic configuration in a single FePc molecule. We here address our investigation to treat a single FePc on a MgO(001) substrate. The HOMO and LUMO states, governed by the Fe 3$d$-orbitals of the FePc molecule, clearly remains in the MgO band gap as seen in the isolated molecule, which gives rise to the ground state of the $^{\mathrm{3}}$B$_{\mathrm{2g}}$ electronic configuration. The transition in the electronic configurations is explained by a weak hybridization between the Fe $d_{\mathrm{z2}}$ and O $p_{\mathrm{z}}$ orbitals at the molecule-substrate interface. [1] S. Nakashima et al., Jpn. J. Appl. Phys. \textbf{52}, 110115 (2013). [2] K. Nakamura et al., Phys. Rev. B \textbf{85}, 235129 (2012). [Preview Abstract] |
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H1.00268: Direct calculation of correlation length based on quasi-cumulant method Noboru Fukushima We formulate a method of directly obtaining a correlation length without full calculation of correlation functions, as a high-temperature series. The method is based on the quasi-cumulant method, which was formulated by the author in J. Stat. Phys. 111, 1049-1090 (2003) as a complementary method for the high-temperature series expansion originally for an SU($n$) Heisenberg model, but is applicable to general spin models according to our recent reformulation. A correlation function divided by its lowest-order nonzero contribution has properties very similar to a generating function of some kind of moments, which we call quasi-moments. Their corresponding quasi-cumulants can be also derived, whose generating function is related to the correlation length. In addition, applications to other numerical methods such as the quantum Monte Carlo method are also discussed. [Preview Abstract] |
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H1.00269: Magnon breakdown in a two dimensional triangular Heisenberg antiferromagnet LuMnO$_{3}$ Joosung Oh, Manh-Duc Le, Jaehong Jeong, Je-Geun Park, Jung-Hyun Lee, Wan-Young Song, T.G. Perring, Hyungje Woo, W.J.L. Buyers, S-W. Cheong Magnons, the quasi-particles of long range ordered magnetic systems, have long been viewed as long lived excitations with spectra that are well described by linear spin wave theory (LSWT). Recent theoretical works, though, suggest that the magnon spectrum of 2D triangular Heisenberg antiferromagnet (THA) is highly renormalized downward with a roton-like minimum at the M point. This, as well as the decay of single magnons into two magnon states, was interpreted as the effects of a cubic interaction between magnons arising from the noncollinear spin structure LuMnO$_{3}$ is a good 2D THA candidate to test this prediction since it has a noncollinear 120$^{\circ}$ spin structure with S$=$2. We have conducted inelastic neutron scattering experiments using a LuMnO$_{3}$ single crystal. Much of the observed spectrum is well described by LSWT, but, a closer inspection of the M point show deviations: a minimum at the lowest energy mode, a flat dispersion at upper modes and line width broadening at the top of the dispersion due to magnon decay. These features agree qualitatively with the theoretical predictions, revealing the importance of the cubic interaction between magnons in 2D THA [Preview Abstract] |
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H1.00270: SDW State Within The Two-Band Model for Iron Pnictides: Role of Hund's Coupling Nimisha Raghuvanshi, Avinash Singh Following the recent discovery of superconductivity in doped iron pnictides such as RO$_{\mathrm{1-x}}$F$_{\mathrm{x}}$FeAs (R $=$ La, Ce, Nd, Sm, Gd) and A$_{\mathrm{1-x}}$B$_{\mathrm{x}}$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$ (A $=$ Ba, Sr, Ca, B $=$ K, Cs, Na), there has been great interest in their magnetic as well as superconducting state. We have investigated the spin wave excitations and the stability of the (0, $\pi )$ ordered spin density wave (SDW) state within the minimal two-band (d$_{\mathrm{xz}}$ and d$_{\mathrm{yz}})$ model for iron pnictides including a Hund's coupling term. The spin wave dispersion indicates the stability of SDW state in two distinct doping regimes; for finite hole doping in the lower SDW band for small NNN hoppings, and for low electron doping in the upper SDW band for comparable NN and NNN hoppings. Hund's coupling strongly stabilizes the SDW state in both the cases due to the generation of additional ferromagnetic spin couplings involving the inter-orbital part of the particle-hole propagator. The spin wave energies for the two-band model are in agreement with the inelastic neutron scattering studies of iron pnictides and similar to the one-band t-t' Hubbard model results obtained in our earlier work. [Preview Abstract] |
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H1.00271: Magnetic resonance in ferromagnetic films, multilayers and nanoparticle composites Natalia Noginova, Brittany Bates, Nicole Greene Incorporation of magnetic materials into metamaterial systems provides an opportunity to tune microwave permeability with external magnetic field. We studied magnetically dependent microwave properties of polymer composites with iron oxide nanoparticles, ferromagnetic films and ferromagnetic/dielectric multilayers. We show that the permeability of such systems can be magnetically tuned from positive to negative values in the range of ferromagnetic resonance, strongly affecting wave propagation. Strong changes in mu-metal permeability in low field range provides an additional possibility of tuning. [Preview Abstract] |
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H1.00272: High frequency magnetic properties of FeCoSiB thin films Ravi Hadimani, Mangui Han, David Jiles Currently, high frequency properties of magnetic materials are critical for the performances of many mobile electronic devices. Larger permeability can be obtained in ferromagnetic thin films that are suitable for high frequency applications. We report the high frequency properties of FeCoSiB thin films with different treatments and with different structures (single layer or FeCoBSi/SiO$_{2}$ multilayer). For instance, we have studied the annealing effects on the microwave permeability values. It is found that the as-prepared films and films annealed at 300 $^{\circ}$C for 1 hour are found in amorphous states and to be anisotropic in static magnetic properties. Nanocrystalline grains have been found in the films annealed at 400 $^{\circ}$C for 1 hour, which are isotropic in magnetic properties. With increasing the annealing temperature, the coercivity and saturation magnetic fields are found decreasing. The resonance frequency shows the same varying trend as the saturation magnetic fields. Very large microwave magnetic losses have been found in all the films, which indicate that FeCoSiB films have potential applications in microwave noise attenuation. [Preview Abstract] |
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H1.00273: Na ordering and Co magnetism in a metallic antiferromagnet Na$_{0.825}$CoO$_{2}$ Ben-Li Young, P.-Y. Chu, J. Y. Juang, G.J. Shu, F.C. Chou Sodium cobaltate, Na$_{x}$CoO$_{2}$, originally known as a battery material, has shown other prominent features such as thermoelectricity, magnetism, and superconductivity. For certain Na contents, the Na vacancies are not randomly distributed so that a superlattice structure is formed. We investigated the Na ordering and the Co magnetism in the $x=$0.825 phase of a metallic antiferromagnet, by nuclear magnetic-resonance (NMR) techniques. We successfully derived the three-dimensional superstructure of the Na ordering, and found additional magnetic susceptibility component emerging at 60 K. In addition, a magnetic field-induced glassy behavior near a metamagnetic transition was discovered. [Preview Abstract] |
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H1.00274: Magnetic Phases of the Shastry-Sutherland Model using Projected Entangled Simplex States Trithep Devakul, Adrian E. Feiguin We study the magnetic phases of the Shastry-Sutherland lattice at finite magnetic fields using the Projected Entangled Simplex States (PESS) class of tensor networks. The ground state is calculated via a projection approach by imaginary time evolution at various external fields. We study the convergence of the method and compare to results from Density Matrix Renormalization Group and Tensor Renormalization. We focus on the commensurate phases at low fields and establish the structure of the correlations at several plateaus. [Preview Abstract] |
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H1.00275: Quantitative analysis of spin Hall magnetoresistance in ferrimagnetic insulator/Cu/normal metal trilayer structure Ryo Iguchi, Daichi Hirobe, Kenichi Uchida, Eiji Saitoh A spin current, a flow of spin angular momentum without a charge current, has been attracted much attention in spintronics. As recently demonstrated, a spin current gives rise to a new magnetoresistance effect called spin Hall magnetoresistance (SMR) owing to the interaction between charge and spin currents via the direct and inverse spin Hall effects. [1] SMR has been intensely studied in the ferrimagnetic insulator(FI)/normal metal (NM) bilayer structure both experimentally and theoretically. In contrast, it is not quantitatively investigated in the FI/Cu/NM trilayer structure. The insertion of a Cu layer, which has a long spin diffusion length, between the FI and NM layers is useful for avoiding the possible appearance of an extrinsic proximity effect in NM close to the Stoner ferromagnetic instability such as Pd and Pt. Thus, the quantitative analysis of the FI/Cu/NM system helps to clarify the origin of magnetoresistive behavior observed in the FI/NM system. We studied SMR in the trilayer structure based on the spin diffusion equation and the spin circuit theory, and found that the reported experimental results are well reproduced by our calculation. [1] H. Nakayama et.al. PRL 110, 206601 (2013). [Preview Abstract] |
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H1.00276: Comparison of contact methods for molecular magnetic tunnel junctions Brian Ruderman, Patrick Truitt Self-assembled monolayers (SAMs) have potential application in charge and spin transport devices. A variety of techniques have been established for contacting SAMs with normal metal electrodes for charge transport studies. However, many of these techniques limit the types of SAMs that can be used or are incompatible with ferromagnetic (FM) electrode materials needed for spin transport. We discuss two methods that are promising for observing spin transport in SAMs. In the first method, we deposit FM electrodes on various sacrificial layers, and then transfer the electrodes to a PDMS stamp which can then be gently brought into contact with the SAM. In the second method, we float a layer of graphene on an aqueous surface and bring it into contact with the monolayer; the graphene acts as a barrier that protects the SAM during subsequent deposition of the FM electrode. Using the latter method, we have been able to fabricate non-shorting, molecular tunnel junctions with magnetic electrodes and current densities consistent with transport through an alkane SAM. We will present our findings on the yield and quality of both fabrication methods, as well as our progress towards functioning molecular spintronic devices. [Preview Abstract] |
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H1.00277: Interplay between the spin transfer and spin orbit torques on domain walls at the 5d/3d-alloy interfaces Alan Kalitsov, Sergey Okatov, Pavel Zarzhitsky, Mairbek Chshiev, Julian Velev, William Butler, Oleg Mryasov The manipulations of domain wall (DW) in thin ferromagnetic layers by current and the spin-orbit coupling (SOC) have attracted significant interest [1]. We report two band model calculations of the spin torque (ST) and the spin current (SC) at 5d/3d interfaces with head-to-head, Bloch and Neel DWs. These calculations are based on the non-equilibrium Green Function formalism and the tight binding Hamiltonian including the s-d exchange interactions and the Rashba SOC parameterized on the basis of ab-initio calculations for Fe/W, FeCo/Ta and Co/Pt interfaces. We find that SOC significantly modifies the ST and violates relations between the spin transfer torque and the divergence of the spin current [2]. \\[4pt] [1] I. M. Miron \textit{et al}., Nature \textbf{476}, 189 (2011).\\[0pt] [2] A. Kalitsov \textit{et al}., Phys. Rev. B \textbf{79}, 174416 (2009). [Preview Abstract] |
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H1.00278: Magnetic Moment Enhancement in Mn11Si19 micro-particles Kiyotaka Hammura, Haruhiko Udono, Tomosuke Aono Our paper aims to investigate a size dependence of Mn11Si19 magnetizm experimentally since there has not been a consensus on it. Mn11Si19, one of the family of compounds referred to as highly manganese silicides (HMS). HMS, in general, have attracted attention because of their potential to be used as thermoelectric materials. Investigation of HMS's basic properties is required. We measured magnetization curves in Mn11Si19 both in bulk and in powder (about 5$\mu$m in diameter) states using a SQUID magnetometer at 5K to 300K. We confirmed paramagnetic properties in bulk and soft ferromagnetic ones in powder states. The Arrott plotting was used for an analysis of the powder's data. [Preview Abstract] |
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H1.00279: Ultrafast measurements of the magnetic and structural phase transition of FeRh in the extreme ultraviolet range Dmitriy Zusin, Patrik Grychtol, Emrah Turgut, Henry Kapteyn, Margaret Murnane, Ronny Knut, Justin Shaw, Hans Nembach, Thomas Silva, Alejandro Ceballos, Catherine Bordel, Peter Fischer, Frances Hellman The temperature dependent transition from the anti-ferromagnetic to the ferromagnetic phase in FeRh is accompanied by a modification of its crystal lattice. In spite of extensive investigations, the interplay between the magnetic and the structural transition is still a matter of strong debate. A better understanding of the phase transition mechanism(s) is important, since the transition can be induced by femtosecond laser pulses and does not seem to be limited by heat transfer, as is the case in magnetic phase transitions that occur on longer (nanosecond) time scales. In this work, we use extreme ultraviolet radiation generated by a tabletop high harmonics source to perform element-selective investigations of the temperature-dependent magneto-optical response of a thin film FeRh sample. We study the optically induced phase transition using two ultrafast pump-probe spectroscopy approaches: by monitoring the time-resolved transversal magneto-optical Kerr effect (T-MOKE) and the transient change in reflectivity. [Preview Abstract] |
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H1.00280: Dynamic exchange coupling and spin pumping in ferromagnetic/normal metal bilayer Roberto Rodriguez, Sergio Rezende, Antonio Azevedo It is known that in ultra-thin ferromagnetic (FM) layers in contact with normal metals (NM), the spin pumping is the most important magnetic relaxation channel. In this work we present a detailed calculation of the NM thickness dependence of the magnetic relaxation in FM/NM bilayers. To calculate the relaxation rate we consider that at the FM/NM interface the spins of the FM layer interact with the NM conduction electron spins through the s-d exchange interaction. The coupled motion of the FM magnetization with the NM spin accumulation transfers to the FM magnetization an additional relaxation from the overdamped motion of the conduction electron spins in the NM layer. We compare our results with the well know treatment that consider only spin currents and show that both yield the same result. [Preview Abstract] |
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H1.00281: Exploration of the new class of layered III-VI Diluted Magnetic Semiconductors (DMS) Thomas Pekarek, I. Miotkowski, A.K. Ramdas We have explored a new class of quasi-two-dimensional III-VI Diluted Magnetic Semiconductors (DMS) exhibiting a wide range of magnetic behavior. Several are good candidates for potential device applications. In In1-xMnxSe, we found a remarkably large thermal hysteresis (Delta T is approximately 200 K) extending up to room temperature. This is an important material because a typical thermal hysteresis in most materials has a Delta T approximately 20 K occurring well below room temperature. The thermal hysteresis is also seen in transport measurements for In1-xMnxSe. To date, we have found good agreement between experiment and theory for the 1st three III-VI DMS systems (In1-xMnxSe, In1-xMnxS, and Ga1-xMnxS). Ga1-xFexSe is unique amount the III-VI DMS exhibiting substantial magnetic anisotropy. In Ga1-xMnxS, we have found a spin glass transition and critical exponents ($\gamma \quad =$ 4.0, $\beta \quad =$ 0.8, and $\delta \quad =$ 5.5) that are in agreement with the theory. We surprisingly found that the spin glass transition in the 2-D III{\-}VI DMS similar to spin glass in 3-D II-VI DMS. [This research was supported by the UNF Terry Presidential Professorship, a Purdue University Academic Reinvestment Program and by the National Science Foundation (NSF) Grant Nos. DMR-07-06593 and DMR-04-05082.] [Preview Abstract] |
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H1.00282: Skyrmion dynamics with spin waves Yizhou Liu, Jiadong Zang, Gen Yin, Shanshan Su, Roger Lake A magnetic Skyrmion is a topological stable spin texture configuration that has attracted wide attention due to its unique properties such as the Topological Hall Effect and current-driven motion. The interaction between a magnon and a single Skyrmion has been studied recently. There are still many questions concerning the interaction of magnons and multiple Skyrmions in confined geometries. We theoretically study the interaction between magnons and Skyrmions by micromagnetic simulations. We simulate Skyrmion dynamics in some various confined geometries to observe their behavior. These interesting properties may be useful for future Skyrmion-based spintronic devices. [Preview Abstract] |
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H1.00283: Structural, Specific heat and Magnetic Studies in YCrO$_{3}$ Doped with Praseodymium Eduardo Verdin, Alejandro Duran, Francisco Morales, Roberto Escudero Many applications and critical phenomena have been found in perovskite type compounds as ferroelectricity, ferromagnetism, multiferroicity among others. Materials that simultaneously show ferromagnetism and ferroelectricity have recently seen a significant revival based on the discovery of new compounds with a strong multiferroic coupling. One of these is the orthochromites family since both phenomena coexist in the same crystal structure. Here, we was studied the magnetism, specific heat and ferroelectric characteristics of the YCrO3 doped with Pr. Rietveld analysis shows that cell volume decreases as Pr doping. Besides, the Dzyaloshinskii-Moriya (D-M) exchange interaction depends of the Pr doping degree as a consequence a negative magnetization and strong changes in the coercive field appear. Here, these results are presented.. [Preview Abstract] |
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H1.00284: Effect of Cu doping on the magnetism of MnCo$_{2}$$_{-}$$_{x}$Cu$_{x}$O$_{4}$ cubic spinels S.K. Singh, M.S. Seehra, S. Thota MnCo$_{2}$$_{-}$$_{x}$Cu$_{x}$O$_{4}$ is a cubic spinel whose magnetic properties are not yet properly understood [1]. Here we report changes in the magnetic properties of MnCo$_{2}$$_{-}$$_{x}$Cu$_{x}$O$_{4}$ samples with change in {\it x} = 0, 0.05 and 0.20. X-ray diffraction measurements of the samples, synthesized by the sol-gel method followed by calcination at 700 $^\circ$C for 2 hours, showed lines only due to the cubic spinel phase without any CuO impurity. Measurements of the magnetization ``M'' vs. temperature ``T'' in H=100 Oe for the ZFC and FC modes showed ferrimagnetic ordering at T$_{c}$ = 175 K, 175 K and 166 K for {\it x} =0, 0.05 and 0.20 samples, respectively. However, for T ${\ll }$T$_{c}$, M for { \it x} = 0.05 (0.20) is smaller (larger) by a factor of three (five) as compared to that for the {\it x} = 0 sample. Hysteresis loops for the {\it x} = 0.20 sample show strong domain wall pinning. These unusual changes in the magnetic properties observed with Cu doping will be discussed in terms of changes in the site occupancies of Cu$^{2+}$ ions on the A and B sites [2]. \\[4pt] [1] P.A. Joy et al, J. Magn. Magn. Mater. 218, 229 (2000).\\[0pt] [2] J. D. Rall et al, Appl. Phys. Lett. 100, 252407 (2012). [Preview Abstract] |
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H1.00285: On the difference between the pyroxenes LiFeSi$_{2}$O$_{6}$ and LiFeGe$_{2}$O$_{6}$ in their magnetic structures and spin orientations Changhoon Lee, Jisook Hong, Ji Hoon Shim, Myung-Hwan Whangbo The clinopyroxenes LiFeSi$_{2}$O$_{6}$ and LiFeGe$_{2}$O$_{6}$, crystallizing in a monoclinic space group P2$_{1}$/c, are isostructural and isoelectronic Their crystal structures are made up of zigzag chains of edge-sharing FeO$_{6}$ octahedra containing high-spin Fe3$+$ ions, which run along the c direction. Despite this structural similarity, the two have quite different magnetic structures and spin orientations. In LiFeSi$_{2}$O$_{6}$ the Fe spins have a ferromagnetic coupling within the zigzag chains along $c$ and such FM chains have an antiferromagnetic coupling along $a$. In contrast, in LiFeGe$_{2}$O$_{6}$, the spins have an AFM coupling within the zigzag chains along $c$ and such FM chains have an $\uparrow \uparrow \downarrow \downarrow $ coupling along $a$. In addition, the spin orientation is parallel to $c$ in LiFeSi$_{2}$O$_{6}$, but is perpendicular to $c$ in LiFeGe$_{2}$O$_{6}$. To explain these differences in the magnetic structure and spin orientation, we evaluated the spin exchange parameters by performing energy mapping analysis based on LDA$+$U and GGA$+$U calculations and also by evaluating the magnetocrystalline anisotropy energies in terms of GGA$+$U$+$SOC and LDA$+$U$+$SOC calculations. Our study show that the magnetic structures and spin orientations of LiFeSi$_{2}$O$_{6}$ and LiFeGe$_{2}$O$_{6}$ are better described by LDA$+$U and LDA$+$U$+$SOC calculations. [Preview Abstract] |
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H1.00286: Gilbert damping up to 300 GHz in Ni81Fe19 Yi Li, A.-L. Barra, S. Auffret, U. Ebel, W.E. Bailey High magnetic fields ($>$10 T) at central facilities, combined with frequency sources approaching 1 THz, enable studies of ferromagnetic resonance (FMR) in a new frequency range. To date, the upper frequency limit of FMR studies of the technologically important alloy Ni$_{81}$Fe$_{19}$ (Py) has been 70 Ghz. No experiments have addressed whether the relatively high levels of Gilbert damping $\alpha$ in this alloy (6-9$\times10^{-3}$), described by $\Delta H=\Delta H_0 +\alpha\omega/\gamma$, where $\Delta H$ is the field-swept linewidth, $\Delta H_0$ is the inhomogeneous broadening, and $\omega/2\pi$ is the microwave frequency, represent a low-frequency limit of richer behavior near THz frequencies. In this work, we compare perpendicular FMR measurements of Ni$_{80}$Fe$_{20}$(5nm) between 4-24 GHz, using a laboratory electromagnet and coplanar waveguide, with measurements at 331.2 GHz and 4-295 K using a 16 T superconducting magnet. We find a consistent Gilbert-type damping between the low- and high-frequency data, with the former predicting a linewidth of $193.4\pm9.5$ mT from the extrapolation and the latter resulting $189.8\pm6.2$ mT. [Preview Abstract] |
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H1.00287: Anomalous Nernst Effect with Magnetocrystalline Anisotropy (110) Carlos Chesman, Jose Costa Neto When a ferromagnetic material is submitted to a temperature gradient and the magnetic field generates voltage on the edges of the samples, this is called the Anomalous Nernst Effect (ANE). The Heusler alloys that currently exhibit this effect are the most promising for spintronics and spin caloritronics. In this study we perform a theoretical investigation of voltage curves associated to the ANE, when the material displays magnetocrystalline anisotropy for experimental results in two configurations, ANE versus applied magnetic field and planar angle variations of ANE. We analyzed three types of magnetocrystalline anisotropy: cubic anisotropy (100) with C4 symmetry, uniaxial anisotropy with C2 symmetry and cubic anisotropy (110). The aim was to prove that cubic anisotropy (110) is equivalent to anisotropy (100) combined with uniaxial anisotropy. Theoretical fitting of experimental ANE data demonstrates this total equivalence and that a new interpretation with the use of cubic anisotropy (110) may be due to the atomic arrangement of the so-called full-Heusler. Comparative analyses of Co$_{\mathrm{2}}$FeAl and Co$_{\mathrm{2}}$MnGe alloys will be presented. [Preview Abstract] |
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H1.00288: Micromagnetic investigations of spatial fluctuations of the first order perpendicular anisotropy in thin films Sergei Wallace, Andrew Tuggle, Matthias Buchmeier, Claudia Mewes, Tim Mewes We report on micromagnetic investigations of spatial fluctuations of the first order perpendicular anisotropy constant K1 in thin films and their influence on the effective anisotropy constant for these materials. In particular we show that spatial fluctuations of K1 on a sufficiently small length scale lead to a second order anisotropy constant K2. Such a second order perpendicular anisotropy constant is frequently assumed in the literature based on a phenomenological approach, without a model for its physical origin. Based on arguments similar to Slonczewski's for explaining the biquadratic exchange coupling (Phys. Rev. Lett.\textbf{ 67}, 3127 (1991)) one expects that fluctuations of K1 will lead to a significant K2. In the limit of small-scale fluctuations one expects this fluctuation induced K2 to scale with the square of the magnitude of the first order anisotropy fluctuations $\Delta $K1 and the square of the characteristic length scale L of the fluctuations (JMMM \textbf{236}, 339 (2001)). The sign of the induced K2 is such that it can lead to an `easy cone' magnetization. In addition to investigations of the quasi-static properties we will also discuss how the spatial fluctuations influence the dynamic properties of thin films. [Preview Abstract] |
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H1.00289: Role of magnetoelastic coupling in magnetic anisotropy of Co$_{2}$(Fe)MnSi thin films Himanshu Pandey, P.K. Rout, Anupam Guleria, P.C. Joshi, Z. Hossain, R.C. Budhani The influence of epitaxial strain on uniaxial magnetic anisotropy of Co$_{2}$Fe(Mn)Si [CF(M)S] Heusler alloy thin films grown on (001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is susceptible to tune by varying the thickness of the films on STO, while on MgO the films show in-plane easy axis for magnetization irrespective of their thickness. The analysis of magnetic free energy functional within the Stoner-Wohlfarth coherent rotation model with out-of-plane uniaxial anisotropy for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant $\sim$ (12.22$\pm$0.07)$\times$10$^{-6}$ and (2.02$\pm$0.06)$\times$10$^{-6}$, in addition to intrinsic magnetocrystalline anisotropy $\sim$ -1.72$\times$10$^{6}$ erg/cm$^{3}$ and -3.94$\times$10$^{6}$ erg/cm$^{3}$ for CFS and CMS, respectively. The single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane orientation of magnetization with the decreasing film thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The distinct behaviour of magnetization in the films with lower thickness on STO is attributed to strain-induced tetragonal distortion. [Preview Abstract] |
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H1.00290: Spin and orbital moments of Co-carbide nanoparticles for permanent magnet applications D.A. Arena, G.E. Sterbinsky, K.J. Carroll, H. Yoon, S. Meng, Z.J. Huba, E.E. Carpenter Many efforts are currently devoted to the development of rare earth free permanent magnets (REFPMs). In newly developed permanent magnet materials, examination of the atomic scale magnetic properties is critical to gaining knowledge of the mechanisms of magnetism and hence furthering the development of these materials. X-ray magnetic circular dichroism (XMCD) is a core-level technique ideally suited for such studies as it provides element-specific information on magnetic properties. We present an XMCD study of the REFPM nanoparticulate Co-carbide using a new high-field end-station at beamline U4B of the National Synchrotron Light Source. This end-station facilitates measurement of XMCD spectra from magnetically hard materials. The Co-Carbide nanoparticles (NPs) under study are synthesized via wet chemical methods, which can lead to differences between the atomic and magnetic structures of the surface and bulk of NPs. To separate the determination of the surface and bulk magnetic properties we have combined our XMCD measurements with in-situ surface treatment. Preliminary measurements of Co L-edge XMCD spectra and element specific hysteresis point to the role of the Co orbital and spin moments in the establishment of the high coercive field and $(BH)_{max}$ in Co-carbide NPs. [Preview Abstract] |
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H1.00291: Electric-field control and effect of Pd capping on interface magnetocrystaline anisotropy of FePd-based thin films Phuong-Vu Ong, Nicholas Kioussis, P. Khalili Amiri, K.L. Wang, Gregory P. Carman, Ruqian Wu Using \textit{ab initio} electronic structure calculations, we investigate effects of electric field and heavy metal cap of Pd on magnetocrystalline anisotropy (MCA) of FePd ultrathin film. It is revealed that while Pd ions favor in-plan MCA, perpendicular MCA of the thin film is mainly due to the spin-orbit coupling between unoccupied Fe $d_{xy}$ and occupied Fe $d_{x^{2}-y^{2}}$ states. The sensitivity of the surface anisotropy energy to applied electric field is 18 fJ.V$^{-1}$.m$^{-1}$. By mapping distributions of $d$-orbital characters over electronic states, mechanism of the field control of anisotropy is elucidated. Furthermore, MCA of the thin film is shown to be strongly affected by Pd capping and a switching from perpendicular to in-plane anisotropy can be obtained by tuning the capping thickness. The effect is explained by spin-orbit couplings of the spin-polarized quantum well states induced by the Pd cap. These results are of practical importance since in magnetic junctions the ferromagnetic layer is mostly capped by a heavy metal electrode. [Preview Abstract] |
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H1.00292: Azimuthal angular dependence of exchange bias in FeMn/Py bilayers with Ta/Cu hybrid underlayers: Effect of deposition sequence and sense of rotation Ki-Yeon Kim, Hyeok-Cheol Choi, Chun-Yeol You We have investigated the azimuthal angular dependent exchange bias of bottom-pinned Py(5nm)/FeMn(5nm) and top-pinned FeMn(5nm)/Py(5nm) bilayers prepared at the same deposition condition except deposition order by vector MOKE experiment. It was found that exchange biased (EB) direction is not collinear with an applied magnetic field during deposition. Second, the critical angle at which the phase of a transverse loop reverses is once (160$^{\circ}$ @CCW, 170 $\sim$ 175$^{\circ}$ @CW) for Py/FeMn bilayer and twice (155 $\sim$ 160$^{\circ}$, 340 $\sim$ 345$^{\circ}$ @CCW, 10 $\sim$ 15$^{\circ}$, 195-200$^{\circ}$ @CW) for FeMn/Py bilayer. Therefore, phase of transverse loop remains the same as the initial transverse loop or reverse after 360$^{\circ}$ rotation, depending on deposition sequence. Third, hysteresis is observed in the transverse magnetization component only if hysteresis loops are measured consecutively between cw and ccw directions over the angular range including the critical angle. This is considered to originate from thermally activated irreversible rearrangement of uncompensated AF spins via interface exchange coupling. Fourth, exchange bias field and coercivity of top-pinned FeMn/Py bilayers with Ta/Cu underlayers are enhanced compared with those of bottom-pinned Py/FeMn bilayers. This is in consistent with our previous results. [Preview Abstract] |
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H1.00293: Magnetic properties of a two-dimensional spin 1 easy axis Heisenberg antiferromagnet with competing interaction Antonio Pires, Griffith Sousa The square lattice antiferromagnet with next and next nearest neighbor exchange interaction has been the subject of intense research in the last years. It can present the behavior of a frustrated system and can otherwise describe real materials. However, a large part of the work has been dedicated to spin 1/2 and done at zero temperature. A system with spin 1 is of interest because it can have a single ion anisotropy. To study these models simple approaches which yield an analytical description are very useful for practical purposes. Here we use a Modified Spin Wave theory, where corrections owing to spin wave interactions are taken into account self-consistently, to study the easy axis two dimensional spin 1 antiferromagnet with competing interaction and single ion anisotropy. We calculate the phase diagram at zero temperature, and several thermodynamic quantities such as the magnetization, the gap and the specific heat. Their relations with the temperature and anisotropy parameter are analyzed over the entire range of temperature. We have found a Neel and a collinear phase separated by a disordered phase. This disordered phase could be a candidate for a spin liquid. [Preview Abstract] |
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H1.00294: Fermionic Representation of a Spin S chain Using subalgebra of SU(2S+1) Solomon F. Duki, Yi-Kuo Yu Quantum mechanical spins behave neither as pure bosonic nor as pure fermionic operators. Over the years many different kinds of important mappings have been introduced that transform spins systems in to either multi-bosonic or multi-fermionic systems. These mappings have often successfully transformed some of the most difficult many body problems into simpler ones. Moreover, because symmetries that are hidden in one representation can be manifested in other representations, such mappings are also helpful in uncovering hidden symmetries in physical problems. Examples of such transformations include the Holstein-Primakoff, the Schwinger bosons, the Matsubara-Matsuda, and the Jordan-Wigner transformations. Despite their success for low dimensional systems and at smaller values of spins, these transformations become ineffective in reducing the degree of difficulty of correlated systems when the system dimension increase or when the underlying system has a higher spin values. In the context of a spin chain, we introduce a new spin fermion transformation for arbitrary spin S using the subalgebra of the bigger su(2S+1) algebra and discuss its potential applications in physical problems. [Preview Abstract] |
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H1.00295: Magnetic Phase Transitions in Nanostructured Mn-intercalated TaS$_{2}$ Paul Shand, Corbyn Mellinger, Corey Cooling, Kayla Boyle, Tim Kidd, Laura Strauss Samples of nanostructured Mn-intercalated TaS$_{2}$ with different concentrations of Mn have been fabricated. Previous work on nanostructured Mn$_{x}$TaS$_{2}$ has shown that ferromagnetism competes with a cluster-glass phase as the atomic fraction $x$ of Mn increases. There is a tricritical point near $x=$ 0.23 as indicated by critical exponent values significantly greater than those associated with the three-dimensional Ising or Heisenberg models. To further understand the phase diagram, we have studied nanostructured Mn$_{x}$TaS$_{2}$ with $x=$ 0.235. dc magnetization and ac susceptibility measurements indicate that there are two transitions as the temperature is varied. Arrott-Noakes and Kouvel-Fisher analyses indicate a ferromagnetic transition at $T_{C}=$ 74 K, with critical exponent values $\beta =0.86$ and $\gamma =1.22$. The anomalous $\beta $ value associated with the ferromagnetic transition was also seen in the sample that exhibited tricritical-like behavior. There is a sharp increase in the susceptibility as the temperature is lowered, with a peak occurring near 40 K. An excellent Vogel-Fulcher fit to the dynamic susceptibility data confirms a cluster glass transition. Our current results are consistent with a steep boundary between the ferromagnetic and cluster-glass phases. [Preview Abstract] |
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H1.00296: First-principles studies of the piezomagnetic effect in transition-metal fluorides Sai Mu, Kirill Belashchenko The piezomagnetic effect can facilitate the manipulation of magnetization by strain, especially in combination with a piezoelectric element. We formulate a model suitable for the first-principles evaluation of the piezomagnetic coefficients and apply it to the series of transition-metal fluorides (MnF$_{\mathrm{2}}$, FeF$_{\mathrm{2}}$, CoF$_{\mathrm{2}})$. The longitudinal piezomagnetic tensor component $\Lambda_{\mathrm{zxy}}$ reaches a maximum at finite temperature similar to the longitudinal magnetoelectric susceptibility. This component is due to the symmetry-breaking response of the parameters of the microscopic spin Hamiltonian to strain, which is calculated from first principles. The transverse component $\Lambda_{\mathrm{xyz}}$, which is entirely due to spin-orbit coupling, is evaluated by minimizing the total energy with respect to the canting of the local moments. The results are compared with available experimental data. [Preview Abstract] |
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H1.00297: Synthesis and Magnetic Characterization of Maghemite Nanoparticles Designed for Targeted Cancer Therapy K. Pisane, E. Despeaux, P.M. Gannett, M.S. Seehra Adopting the procedure described by Hyeon et al [1], oleic acid coated maghemite nanoparticles of 7 nm average size as determined by TEM were synthesized for use in targeted cancer therapy. Here we report their magnetic properties. Using a PPMS magnetometer, magnetization (M) vs. temperature (2 K - 350 K) and magnetic field (up to $\pm$ 90 kOe) was measured under the zero-field-cooled (ZFC) and field-cooled (FC) conditions. The results for H $=$ 100 Oe show a blocking temperature $T_{B} =35K$ which shifts to lower temperatures with increase in H. For$T > T_{B}$, isotherms of M vs. H were measured at several temperatures and, following the procedures reported recently [2], data were fitted to a modified Langevin function: $M=M_{0} L(\mu_{p} H/k_{B} T)+\chi_{a} H$ with $\mu_{p} \simeq 7500\mu _{B} $ per particle. Using this magnitude of $\mu_{p} $, particle diameter D $=$ 6.9 nm is determined which agrees with the TEM data. Procedures for \textit{in vitro} studies include coating with biocompatible polymer and functionalization with therapeutic and targeting ligands. Toxicity testing and determination of \textit{in vivo} activity are in progress.\\[4pt] [1] T. Hyeon et al, J. Am. Chem. Soc. 123, 12798 (2001)\\[0pt] [2] M. S. Seehra et al, J. Phys. Chem. Solids 71, 1362 (2010) [Preview Abstract] |
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H1.00298: On the Cubic Phase Stability and Magnetic Properties of Cu-doped ZrO$_{2}$ S. Thota, K. Pisane, S. Singh, M.S. Seehra Magnetic properties and room temperature cubic-phase stability of Cu-doped ZrO$_{2}$ nano-crystallites (16 nm size) with various compositions of Zr$_{1-x}$Cu$_{x}$O$_{2-x}$ (0.01$\le $x$\le $0.25) are reported. The samples were synthesized at a constant pH $=$ 8 using zirconyl nitrate hydrate and copper acetate monohydrate as precursors and ethanol as a solvent. Thermal analysis shows that the cubic phase is not stable beyond calcination temperature of 500$^{\circ}$C for 8 hours in air and a critical composition x$_{c} \approx $ 0.10. For x \textgreater x$_{c}$ , monoclinic ZrO$_{2}$ and CuO emerge as secondary phases with a shrinking unit-cell volume for increasing Cu content. Against expectations [1], the temperature and magnetic field dependence of magnetization exhibit no signatures of ferromagnetism down to 2 K. Instead, temperature dependence of magnetic susceptibility for all compositions yields Curie-law variation with a magnetic moment $\mu \approx 1.3\mu_{B} $ per Cu$^{2+}$, which is somewhat smaller than the expected value of $\mu \approx 1.9\mu_{B} $ per Cu$^{2+}$. Electron magnetic resonance studies show a signal near g $\approx $ 2.1 due to Cu$^{2+}$ substituting at Zr$^{4+}$ sites with four-line hyperfine splitting from the nuclear spin I $=$ 3/2 of Cu.\\[4pt] [1]. S. Ostanin et al, Phys. Rev. Lett. 98, 016101,(2007) [Preview Abstract] |
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H1.00299: PHYSICS OF CLIMATE |
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H1.00300: Climate Variability and Local Land Use in the Upper Midwest Zachary Klassen, Josef Wieber, Sylke Boyd We have analyzed the longitudinal weather records from 12 distinct weather stations in Minnesota and the Dakotas in conjunction with long-term changes in land use in those locations including diurnal temperature range, precipitation, daily maximum, minimum, and mean temperatures and other data. The land types include rural cultivated land, urban areas and forest. One motivation for this study was to investigate the role of the transition from prairie land to high-evapo-transpiration crops such as soy and corn. The weather records were obtained from the National Climatic Data Center of the National Oceanic and Atmospheric Administration. We observe an increase in the extreme minimum temperatures throughout all months of the year. The increase in minimum temperatures is most pronounced for the northern-most locations in the dataset and for the winter months. Consistent with similar observations from other US locations, the mean daily temperature range has a decreasing trend for all non-urban locations. Urban locations are showing clear heat-island effects of increases in all temperature markers but no significant variations in daily temperature range. No significant difference in trends was found between cultivated and forested locations. [Preview Abstract] |
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H1.00301: Data collection and analysis on Halo displays using an all-sky camera Stephen Sorenson, James Froberg, Sylke Boyd Observations of atmospheric optical phenomena can reveal much about the physical properties of the troposphere. The goal is to set up a facility for long-term observation and data collection on frequency and type of optical displays at the University of Minnesota-Morris.We aim to utilize these optical phenomena for remote observation of atmospheric conditions that influence the ice crystal shapes, sizes, orientations and particle densities in cirrus altitude. They affect the color, angular intensity distribution, brightness and type of optical displays. An all-sky camera is sampling the sky at regular intervals. We present our work on image analysis software for the automatic detection of the presence of common halo-related optical phenomena. This will allow systematic cataloguing as well as data on frequency and seasonal distribution of the various types of displays for our area. We also present a Matlab simulation correlating the observed angular intensity distribution with the types, sizes and orientations of ice crystals present in the generating layer. Based on sequences of refraction and reflection processes on the various surfaces of the ice crystal, the exit angle distributions for large numbers of incident rays are compiled. [Preview Abstract] |
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H1.00302: CO2 exchange over a mixed-grassland savanna in Central Brazil Paulo Arruda We used eddy covariance technique to measure the net ecosystem exchange (NEE) of CO$_{2}$ between the atmosphere and an savanna in Central Brazil (locally known as cerrado), from February 2011 to February 2013, the data set included measurements of climatological variables. This part of brazilian savana has a long history of land cover change due to human activity, mainly due agricultural activity. Thus, the aim of this study was to evaluate the temporal variation in energy flux in areas of degraded, grass-dominated cerrado (locally known as \textit{campo sujo}) in Central Brazil. The NEE variability is controlled mainly by solar radiation, temperature and air humidity on diel course. Seasonally, soil moisture and changes on land cover plays a strong role on the ecossystem. Daytime CO2 uptake under high irradiance averaged 4-12 $\mu$ mol$\cdot$m$^{-2}$ $\cdot$ s$^{-1}$ in the wet season (October to April) and 0-3 $\mu$ mol $\cdot$ m$^{2}$ $\cdot$ s$^{-1}$ on the dry season (May to September). The net sign of NEE is negative (sink) during of the wet season and positive (source) in the dry season. [Preview Abstract] |
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H1.00303: FLUIDS |
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H1.00304: A water flow molecular dynamics simulation in a methyl functionalized imogolite nanotube Nathan Cannon, Takumi Hawa Some nanotubes have enhanced water transport properties, but the imogolite nanotube, which is a hydrous aluminosilicate nanotube, is not known to and we suspect that it does not. To achieve enhanced water transport, its inner surface was made hydrophobic by replacing an OH group with a CH3 group. The performance of the natural and modified imogolites was measured by inducing water flow and comparing the results with continuum theory using molecular dynamics simulations to determine transport efficiency. Simulations were run using the CLAYFF and CVFF potentials for the nanotube and the SPC/e model for water. The natural imogolite performed 200 times worse than continuum theory, while the modified imogolite performed 10 times better. We also investigated the interaction of the inner surface atoms with the water molecules to help to explain what factors are the most influential in effecting the transport of water. [Preview Abstract] |
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H1.00305: Charged Nanoparticle Translocation through solid state nanopores fabricated using different techniques Santoshi Nandivada, Jiali li, Mourad Benamara Solid-state nanopores are widely used for detection of biomolecules and small particles by measuring the pore resistance change when the molecules or particles are electrophoretically driven through. In this work, we use well-characterized spherical nanoparticles and long chain double-stranded DNA molecules to study the interactions of these nanoparticles and voltage biased solid-state nanopores. Charged nanoparticles of $\sim$ 30nm or smaller are used to study the volume and charge dependence of their translocation dynamics in solid-state nanopores made from silicon nitride. Nanopores fabricated using two different techniques are used in this study: one is to use noble gas ion beams to sculpt $\sim$ 100 nm pores milled by focused ion beam; another is to use e-beam lithography to first write a micrometer size pattern, then to thin the patterned region, and finally drill a nanopore in the thinned micrometer region by a high energy electron beam in a TEM. The 3D geometry of both types of nanopores are measured using HR-TEM . Furthermore, COMSOL is used to model the experimental results. These studies will improve our understanding of solid-state nanopore as a sensor for charged nanoparticle detection. [Preview Abstract] |
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H1.00306: Instabilities of structured liquid metal geometries on nanoscale Nanyi Dong, Yueying Wu, Jason Fowlkes, Philip Rack, Lou Kondic Directed assembly on nanoscale is one of quickly growing fields in materials science, and understanding basic physical mechanisms that lead to formation of desired patterns is crucial for future progress. This contribution, motivated by the experiments carried out with structured metal geometries liquefied by laser irradiation, centers on formulating simple but realistic models that allow to reach this understanding. The model is based on long-wave limit of Navier-Stokes equations relevant to evolution of liquid metals. Liquid-solid interaction forces are included and we show that these are crucial for instability development. We carry out fully nonlinear simulations of the derived model, and find that the computational results are fully consistent with the experimental ones, thus confirming that the main feature of the experiments could be captured by a simplified continuum model. In addition, our simulations suggest that stochastic effects, possibly due to thermal noise, may play an important role. [Preview Abstract] |
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H1.00307: Universality Results for Multi-layer Radial Hele-Shaw Flows Prabir Daripa, Craig Gin Saffman-Taylor instability is a well known viscosity driven instability of an interface separating two immiscible fluids. We study linear stability of this displacement process in multi-layer radial Hele-Shaw geometry involving an arbitrary number of immiscible fluid phases. Universal stability results have been obtained and applied to design displacement processes that are considerably less unstable than the pure Saffman-Taylor case. In particular, we derive universal formula which gives specific values of the viscosities of the fluid layers corresponding to smallest unstable band. Other similar universal results will also be presented. The talk is based on ongoing work. [Preview Abstract] |
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H1.00308: The Lattice Boltzmann Method for quantum fluids and the fourth order Hermite polynomial expansion Mauro Doria, Rodrigo Coelho, Anderson Ilha, Rodrigo Miranda Pereira, Valter Y. Aibe One of the greatest achievements of the Boltzmann equation is to determine the macroscopic hydrodynamical equations (MHE) of a fluid from a phase space distribution function. Nearly eighty years have passed since E. A. Uehling and G. E. Uhlenbeck solved the Bolztmann equation for the quantum fluid and derived their MHE through the so-called Chapman-Enskog analysis, from where they obtained the viscosity and the thermal conductivity coefficients of the quantum fluid. In the late eighties a numerical method was formulated to solve the Boltzmann equation for the classical fluid with the Bhatnagar-Gross-Krook collision term, the lattice Boltzmann method (LBM), that became widely known because of its numerical advantages. Many years after H. Grad devised another method to solve the Boltzmann equation based on an expansion of the distribution function in terms of Hermite polynomials. Here we show that this Hermite polynomial expansion must be carried to fourth order in order to obtain the MHE of the quantum fluid such that its viscosity and thermal coefficients are those obtained from the Uehling-Uhlenbeck approach. Hence we show how an LBM for the quantum fluid must be constructed and numerically solved. [Preview Abstract] |
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H1.00309: Capillary Condensation: an Analysis of the Phase Transition Marie Romano, Anastasia Yorke, Katharyn Christiana, Carolina C. Ilie We explore herein the capillary condensation for planar geometry. Capillary condensation is studied in the presence of van der Waals forces. We derive the grand free energy for one planar substrate, then for two identical substrates, and we analyze the phase transitions, the absorption isotherms and the triple point. Phase transitions between full, empty and two films are investigated and the shape of the liquid between two infinite planes in the transition case between full and film. Other interesting cases may be inspected. [Preview Abstract] |
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H1.00310: Shape Instabilities in Single Bubble Sonoluminescence; Stability, Period Doubling and Bubble Death Mogens Levinsen Excitation of shape instabilities represents one route to bubble death in single-bubble sonoluminescence. By extending the theory for excitation of shape instabilities, represented by expansion in spherical harmonics, to second order, it is shown that the exponential growth into bubble disruption in a certain parameter regime is checked and a saturated stable state of shape distortion is possible. Experimental evidence provided by Mie scattering is presented and a possible connection to simultaneous spatially anisotropic light emission discussed. Implications for the mechanism behind bubble death is discussed in connection with the experimental results. [Preview Abstract] |
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H1.00311: Microstreaming from Sessile Semicylindrical Bubbles Sascha Hilgenfeldt, Bhargav Rallabandi, Lin Guo, Cheng Wang Powerful steady streaming flows result from the ultrasonic driving of microbubbles, in particular when these bubbles have semicylindrical cross section and are positioned in contact with a microfluidic channel wall. We have used this streaming in experiment to develop novel methods for trapping and sorting of microparticles by size, as well as for micromixing [1,2]. Theoretically, we arrive at an analytical description of the streaming flow field through an asymptotic computation that, for the first time, reconciles the boundary layers around the bubble and along the substrate wall, and also takes into account the oscillation modes of the bubble. This approach gives insight into changes in the streaming pattern with bubble size and driving frequency, including a reversal of the flow direction at high frequencies with potentially useful applications [3].\\ \\ $[1]$ C. Wang, S.Jalikop, and S.Hilgenfeldt, Appl. Phys. Lett. 99, 034101 (2011). \\ $[2]$ C. Wang, B.Rallabandi, and S.Hilgenfeldt, Phys. Fluids 25, 022002 (2013).\\ $[3]$ B.Rallabandi, C.Wang, and S.Hilgenfeldt, J. Fluid Mech., in press (2013).\\ [Preview Abstract] |
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H1.00312: Velocity profile of water vapor inside a cavity with two axial inlets and two outlets Jos\'e Guadarrama-Cetina, Gerardo Ruiz Chavarr\'Ia To study the dynamics of Breath Figure phenomenon, a control of both the rate of flow and temperature of water vapor is required. The experimental setup widely used is a non hermetically closed chamber with cylindrical geometry and axial inlets and outlets. In this work we present measurements in a cylindrical chamber with diameter 10 cm and 1.5 cm height, keeping a constant temperature (10 $^{\circ}$C). We are focused in the velocity field when a gradient of the temperatures is produced between the base plate and the vapor. With a flux of water vapor of 250 mil/min at room temperature (21 $^{\circ}$C), the Reynolds number measured in one inlet is 755. Otherwise, the temperatures of water vapor varies from 21 to 40 $^{\circ}$C. The velocity profile is obtained by hot wire anemometry. We identify the stagnations and the possibly instabilities regions for an empty plate and with a well defined shape obstacle as a fashion sample. [Preview Abstract] |
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H1.00313: Flow Dynamics on the Reconstitution of Lyophilized Products Dezhuang Ye, Hanyu Song, Robin Bogner, Tai-Hsi Fan Due to stability concern, pharmaceuticals are often freeze-dried before shipping and storage. When needed, sterile water can be injected into the vial to reconstitute the medication. Finding an optimal reconstitution condition for dissolving lyophilized pharmaceutical products is difficult without basic understanding of the relevant fluid dynamics and multiphase mass transfer phenomena. The reconstitution efficiency strongly depends on the normal and shear motions in the solution. The right combination of vial size, shaking pattern, and the amount of solvent would enhance the dissolution rate and reduce the clump formation during the reconstitution process. Here we present the theoretical analysis of shaking pattern in terms of cylindrical traveling and resonant free surface waves under the small-amplitude assumption, and compare the results with direct simulation that can be extended to nonlinear and large-amplitude regimes. The analysis and experimental validation are used to predict a range of pharmaceutical dissolution conditions. [Preview Abstract] |
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H1.00314: POSTDEADLINE |
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H1.00315: A Study of Photoluminiscence and UV-Vis in Enhanced GaN Nanofibers Joshua Robles-Garcia, Anamaris Melendez-Zambrana, Idalia Ramos The photoluminiscence (PL) and UV-Vis properties of Gallium Nitride (GaN) nanofibers were investigated for samples fabricated with a precursor solution containing Gallium Nitrate Hydrate, Cellulose Acetate, and Urea in the solvents Dimethylacetamide (DMA) and Acetone. GaN is a wide bandgap (3.4 eV) semiconductor that can be used in a variety of applications including solid-state lighting, high power, and high frequency devices. In previous work, we produced polycrystalline GaN nanofibers with wurtzite structure, using the electrospinning method and a thermal treatment in nitrogen and ammonia at 1000C. In this research we study the addition of urea to the precursor solution to enhance the crystallinity of the fibers at lower sintering temperatures. The molar ratios of urea added to the precursor range from 0 to 1.7 M. After electrospinning the fibers were sintered in Nitrogen at 450C for 3 hours and then, under ammonia gas flow at 900C for 5 hours. X-Ray Diffraction (XRD), UV-Vis spectroscopy, and PL measurements at room temperature were used to study the structural and optical properties of the fibers during the sintering process. [Preview Abstract] |
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H1.00316: Incommensurate phases of a supported nanoparticle film subjected to uniaxial compression Siheng You, Bran Leahy, Minke Zhang, Yenchao Chua, Ka Yee C. Lee, Susan N. Coppersmith, Binhua Lin We investigate experimentally and theoretically the sequence of phases that occurs when a self-assembled monolayer of gold nanoparticles supported on a fluid is compressed uniaxially in a Langmuir trough. Uniaxial compression of the monolayer results in the appearance of lines that have been shown to be regions of trilayer. These lines exhibit complex patterns that depend on the extent of compression. We show that these patterns can be understood in terms of an equilibrium statistical mechanical theory, originally developed in the context of commensurate--incommensurate transitions in krypton monolayers adsorbed on graphite, in which there is an energy cost to line deformations and to line intersections. Even though line intersections are energetically costly, they lower the free energy because they cause the entropy of the system to increase when the density of lines is low enough. Our analytic and Monte Carlo analyses of the model demonstrate that the model exhibits two-phase coexistence. Our experimental observations are qualitatively consistent with the predictions of the model. [Preview Abstract] |
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H1.00317: Triply-intergrown distorted ths nets: A new tricontinuous equilibrium morphology in copolymeric systems Michael G. Fischer, Liliana de Campo, Stephen T. Hyde, Gerd E. Schroeder-Turk Copolymeric self-assembly provides an efficient route to the formation of ordered 3D nanostructures. The most complex equilibrium structure in diblock copolymer melts is the core-shell Gyroid based on the intergrowth of two continuous network domains. Adaption of the molecular architecture is a strategy to achieve different phases, such as kaleidoscopic columnar phases in star-shaped triblock terpolymers. However, the formation of phases based on more than 2 network domains has not yet been reported in copolymer melts. We show that a triply-periodic tricontinuous structure based on the intergrowth of three nets is a stable equilibrium phase of star-shaped triblock copolymers when an extended core is introduced into the molecules. We use self-consistent field theory to confirm the geometric intuitions why the introduction of the core leads to the formation of this new phase. Its effect is a change in the relative importance of interface tension between the three polymeric species and entropic chain stretching to the free energy. This phase is the first tricontinuous network phase in copolymer melts, which has long-range crystalline order but low symmetry. [Preview Abstract] |
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H1.00318: Ising Lattices of Asymmetric Colloidal Dimers by Short-range Dipolar Attraction under Electric Field Fuduo Ma, Sijia Wang, Hui Zhao, David Wu, Ning Wu Colloids with anisotropic interactions could assemble into much more diversified structures than isotropic particles. Here, we investigate the impact of geometric anisotropy on the assembly of colloidal dimers on conducting substrates under applied electric fields. We have found that interactions between dimers are strongly dependent on their relative orientations. For example, when dimers stand up on the substrate, interaction is attractive between dimers with alternating orientations, while repulsive between dimers with same orientations. Such orientation-dependent interactions bring new structures, such as dimers crystals with alternating orientations. Our numerical model based on dipolar interaction agrees well with experimental results and provides further insights on electric-field assisted assembly of anisotropic particles. [Preview Abstract] |
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H1.00319: Temporal asymmetries in Interbank Market: an empirically grounded Agent-Based Model Vinko Zlatic, Marko Popovic, Hrvoje Abraham, Guido Caldarelli, Giulia Iori We analyse the changes in the topology of the structure of the E-mid interbank market in the period from September $1^{st}$ 1999 to September $1^{st}$ 2009. We uncover a type of temporal irreversibility in the growth of the largest component of the interbank trading network, which is not common to any of the usual network growth models. Such asymmetry, which is also detected on the growth of the clustering and reciprocity coefficient, reveals that the trading mechanism is driven by different dynamics at the beginning and at the end of the day. We are able to recover the complexity of the system by means of a simple Agent Based Model in which the probability of matching between counter parties depends on a time varying vertex fitness (or attractiveness) describing banks liquidity needs. We show that temporal irreversibility is associated with heterogeneity in the banking system and emerges when the distribution of liquidity shocks across banks is broad. [Preview Abstract] |
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H1.00320: Enhanced quantum coherence in graphene caused by Pd cluster deposition and its zero-temperature saturation Fengqi Song, Junhao Han, Baigeng Wang, Guanghou Wang The surface decoration of graphene offers great opportunities because graphene is a fully open system. Functional defects, p/n type doping, spin polarization, and additional spin--orbit interactions can be introduced when atoms are absorbed from an external source. Researchers are even considering inducing topologically nontrivial gaps inside the Dirac cone. Despite the potential advances, however, an important problem remains that surface absorption, along with introducing the required functionality, induces additional electronic scattering Such scattering may suppress the coherence of the Dirac fermions and may even disable these desired quantum states. Here we report on the unexpected increase of the dephasing lengths of a graphene sheet caused by the deposition of Pd nanoclusters, demonstrated by weak localization measurements. The dephasing lengths reached saturated values at low temperatures, essentially related to zero-temperature dephasing. The temperature-dependent dephasing was described by 1/(TlnT) and the saturated dephasing period was found to depend on $\sigma $le. This reveals disorder-induced zero-temperature dephasing in our defect-enriched graphene. Combined with theoretical calculations, we suggest that competition between surface scattering and charge transfer leads to the improvement of quantum coherence in cluster-decorated graphene. (in review) [Preview Abstract] |
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H1.00321: Atom interferometer inertial sensor with radially expanding atom ensemble Stefan Riedl, Greg Hoth, Elizabeth Donley, John Kitching We present our work towards a novel compact atom interferometer inertial sensor based on a single radially expanding ensemble of laser-cooled atoms interrogated by pulsed stimulated Raman transitions. The sensor design emphasizes small size and simplicity of operation, while potentially achieving a performance level suitable for inertial navigation. The expansion of the atom ensemble together with spatially-resolved detection enables to separate acceleration-induced phase shifts from rotation-induced phase shifts, allowing acceleration and rotation to be independently measured. [Preview Abstract] |
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H1.00322: Connecting electron and phonon spectroscopies to consistently determine quasi-particle -- phonon coupling on the surface of topological insulators Colin Howard, Michael El-Batanouny, Fang-Cheng Chou, Raman Sankar Photoemission and phonon spectroscopies have yielded widely varying estimates of the electron-phonon coupling parameter on the surfaces of topological insulators, even for a particular material and technique. We connect the results of these experiments by deter- mining the Dirac fermion quasiparticle spectral function using information from measured spectra of a strongly-interacting, low-lying optical surface phonon band. The manifest spectral features resulting from the coupling are found to vary on energy scales $<$ 1 meV, and are distinct from those traditionally observed in the case of acoustic phonons in met- als. We explore different means of determining $\lambda$ from the electron perspective and identify definitions that yield values consistent with phonon spectroscopy. [Preview Abstract] |
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H1.00323: The effect of oxygen vacancies on the electrical properties of TiO$_{\mathrm{2-x}}$ Re-RAM switching devices Maamar Benkraouda The main goal of this work is to contribute toward an accurate determination of the electronic properties of Resistance random access memory (Re-RAM) using the density functional theory, which is the current state of the art method that employs high accuracy, it can treat a few hundred atoms on medium sized PC. All the fundamental properties are studied as a function of the mole fraction. The density of states arising from vacancy distribution, the electron transport and formation energy are analyzed. Using controllable mole fraction, various intermediate resistance states are induced. Oxygen vacancy has a considerable effect on the electrical properties of most transition metal oxides such as TiOx Re-RAM devices. The presence of oxygen vacancies is linked to the on-state conduction and resistance switching mechanism. Hydrogen is a ubiquitous impurity in most semiconductors, insertion of hydrogen atoms will remove some of defect states which were induced by oxygen vacancies; this will obviously have an effect on the conductive path, because hydrogen in the vacancy site results in the rupture of conductive channel by localizing electrons, the conductivity may decrease in this case. [Preview Abstract] |
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H1.00324: Spin-Orbit Interaction Effect in SrIrO3 Thin Films Yanbin Chen, Shan-Tao Zhang, Yan-Feng Chen Spin-orbit interaction assistant Mott-insulator in Sr2IrO4 induces intensive study to explore the novel phases and corresponding physical properties that results from competition between electron-electron and spin-orbit interaction. In this work, we studied the physical property of SrIrO3 thin films, in which the spin-orbit interaction is larger than electron-electron interaction. In SrIrO3 films, we observed the metal-insulator transition when the thickness of SrIrO3 is thinner than 4 nm. The detailed analysis of temperature-dependent resistance and magnetoresistance substantiate that the metal-insulator transition is attributed to Anderson localization. Spin-orbit interaction plays the crucial role on the magnetoresistance at low magnetic field range (less than 2.5T). By analysis magnetoresistance, we observe that spin-orbit interaction coefficient is strongly dependent on temperature, which is explained by the strongly temperature-dependent g-factor. These studies may shield more light on the physical properties induced by synergetic contribution coming from electron-electron and spin-orbit interaction. [Preview Abstract] |
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H1.00325: Measurement of refractive index distribution of biotissue by scanning focused refractive index microscopy Qing Ye, Tengqian Sun, Jin Wang, Xiaowan Wang, Zhichao Deng, Wenyuan Zhou, Chunping Zhang, Jianguo Tian A novel scanning focused refractive-index microscopy (SFRIM) technique are presented. With a focused laser serves as the light source, we combine the derivative total reflection method (DTRM), microscopy and the scanning technique together to obtain the refractive-index profiles (RIP) of objects. The refractive index (RI) accuracy is 0.002. The central spatial resolution of SFRIM achieves \textit{1 }$\mu m$, smaller than the size of the focal spot. Results of measurements carried out on cedar oil and a gradient-refractive-index (GRIN) lens agree well with theoretical expectations, thereby verifying the accuracy of SFRIM. Refractive index distribution of biotissue are measured by this microscopy. The use of SFRIM opens up possibilities for RIP measurement in many applications, including optical waveguides, photosensitive materials and devices, the study of the photorefractive effect, and RI imaging in biomedical fields. [Preview Abstract] |
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H1.00326: Improvement of Thermoelectric Cooling with Inhomogeneous Thermal Conductivity Jun Zhou, Tingyu Lu, Baowen Li Thermal rectifier with inhomogeneous thermal conductivity has been theoretically proposed [ Li, Wang, and Casati, Phys. Rev. Lett. \textbf{93}, 184301 (2004); Segal and Nitzan, Phys. Rev. Lett. \textbf{94}, 034301 (2005); Terraneo, Peyrard, and Casati, Phys. Rev. Lett. 88, 094302 (2002)] and been experimentally observed in carbon and boron-nitride nanotubes which are mass-loaded externally and inhomogeneously with heavy molecules [Chang et al., Science \textbf{314}, 1121 (2006)]. We theoretically investigate the thermal rectification effect on the thermoelectric cooling process with linearly changed spatial dependent thermal conductivity. We find that the dissipation of Joule heat generated in such thermoelectric devices could be inhomogeneous that is very different from the convention thermoelectric devices. Such inhomogeneity of heat dissipation could enhance the heat absorption at the cold end in cooling and therefore enhance the cooling power. The energy conversion efficiency can also be modified with a redefined thermoelectric figure-of-merit ZT. Our finding is believed to be useful for high performance of thermoelectric devices in the future. [Preview Abstract] |
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H1.00327: Nanomorphological study of polymer bulk heterojuntion used in flexible solar devices Gabriel Calder\'on-Ortiz, Hector Carrasco, Josee Vedrine-Pauleus Solar cells fabricated with organic polymeric materials can enable large area fabrication on printable and flexible substrates, but increasing their efficiency is coupled to understanding their electrical properties and mechanical function on the nanoscale. In this study we measure the nanoscale conducting and mechanical properties of organic bulk heterojunction polymers coated on graphene and flexible PET or Si substrates.~~We characterize the nanomorphology of bulk heterojunction conducting polymers by applying conductive atomic force microscope (c-AFM), and force~volume mapping for quantitative nanomechanical property calculations. [Preview Abstract] |
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H1.00328: Bulk Nuclear Hyperpolarization in Diamond Melanie Drake, Eric Scott, Jonathan King, Jeffrey Reimer Optical pumping in diamonds containing a high density of nitrogen vacancy (NV) centers is shown to generate large bulk 13C spin polarization at high magnetic fields. The phenomenon occurs spontaneously and at room temperature. The sign and magnitude of the nuclear polarization is found to be sensitively dependent on crystal orientation and light polarization. We discuss possible mechanisms for the polarization transfer between the NV and nuclear spins, revisiting a previous model where the thermal contact between the NV ensemble dipolar energy reservoir and the nuclear Zeeman reservoir was used to explain the observed nuclear polarization. [Preview Abstract] |
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H1.00329: e-Learning - Physics Labs Hashini Mohottala The general student population enrolled in any college level class is highly diverse. An increasing number of ``nontraditional'' students return to college and most of these students follow distance learning degree programs while engaging in their other commitments, work and family. However, those students tend to avoid taking science courses with labs, mostly because of the incapability of remotely completing the lab components in such courses. In order to address this issue, we have come across a method where introductory level physics labs can be taught remotely. In this process a lab kit with the critical lab components that can be easily accessible are conveniently packed into a box and distributed among students at the beginning of the semester. Once the students are given the apparatus they perform the experiments at home and gather data All communications with reference to the lab was done through an interactive user-friendly webpage -- Wikispaces (WikiS). Students who create pages on WikiS can submit their lab write-ups, embed videos of the experiments they perform, post pictures and direct questions to the lab instructor. The students who are enrolled in the same lab can interact with each other through WikiS to discuss labs and even get assistance. [Preview Abstract] |
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H1.00330: Physics Teaching Assistants' Experiences in Teaching Nature of Science (NOS) in Physics Laboratories Mehmet Aydeniz, Kubra Yeter-Aydeniz The purpose of this study is to investigate physics teaching assistants' experiences with teaching the nature of science to their students. The participants consist of 10 teaching assistants who had taught various undergraduate physics lab sections at least one semester. Data were collected through an open-ended questionnaire, one semi-structured interview and document analyses. The results show that majority of students have difficulty in appropriating the epistemic norms of science in their laboratory reports. The analyses of lab reports show that students fail to develop robust scientific explanations for the data they gather through experiments. The discussion focuses on enhancing teaching assistants' pedagogical content knowledge for promoting students' adequate understanding and use of NOS in their reports. [Preview Abstract] |
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H1.00331: First-principles analysis of phase stability in layered-layered composite cathodes for lithium-ion batteries Hakim Iddir, Roy Benedek The atomic order in layered-layered composites with composition xLi2MnO3$\cdot$(1-x)LiCoO2 is investigated with first-principles calculations at the GGA$+$U level. This material, and others in its class, are often regarded as solid solutions, however, only a minute solubility of Li2MnO3 in a LiCoO2 host is predicted. Calculations of Co-vacancy formation and migration energies in LiCoO2 are presented, to elucidate the rate of vacancy-mediated ordering in the transition-metal-layer, and thus determine whether low vacancy mobility could result in slow equilibration. The Co-vacancy formation energy can be predicted only to within a range, because of uncertainty in the chemical potentials. Predicted migration energies, however, are approximately 1 eV, small enough to be consistent with rapid ordering in the transition metal layer, and therefore separated Li2MnO3 and LiCoO2 phases. The relatively small (of the order of a few nm) Li2MnO3 domain sizes observed with TEM in some xLi2MnO3$\cdot$(1-x)LiMO2 composites may result from other factors, such as coherency strain, which perhaps block further domain coarsening in these materials. [Preview Abstract] |
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H1.00332: A metrology technique for phosphorus-donor clusters in silicon based on hyperfine splittings Yu Wang, Holger Buch, Lloyd Hollenberg, Gerhard Klimeck, Michelle Simmons, Rajib Rahman The spin states of electrons at phosphorus-donors in silicon are promising candidates for solid-state qubits. A single phosphorus atom in silicon can act as an electron-spin qubit, which shows long relaxation time. However, even with atomically precise fabrication techniques, it is challenging to precisely control the number of phosphorus atoms implanted in silicon. A phosphorus-donor cluster in silicon is an experimentally less demanding alternative for a qubit. Recently, single-shot spin-readout measurements have been performed on phosphorus-donor clusters and show long relaxation time ($\sim$ 2s). However, there is uncertainty in the number of donors, number of electrons and donor locations of a donor cluster, which is difficult to characterize directly in experiments. Since the hyperfine couplings between electron and nuclear spins in a donor cluster are sensitive to variations on an atomic scale, characterization techniques can be devised to extract the configurations of donor clusters based on electron spin resonance, which is useful to design qubit control parameters needed for scaled-up devices. In this work, we propose a unique metrology technique based on large-scale atomistic electronic structure calculations for donor clusters in silicon. [Preview Abstract] |
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H1.00333: Dopant's chemical coordination: a path for engineering high performance thermoelectric sodium cobaltate M. Hussein N. Assadi, Hiroshi Katayama-Yoshida Engineered Na$_{0.75}$CoO$_{2}$ is considered a prime candidate to achieve high efficiency thermoelectric systems to generate electricity from waste heat. Our recent experiments on Mg doped Na$_{0.75}$CoO$_{2}$ demonstrated 50\% enhancement in power factor at ambient. This motivated us to theoretically analyze the mechanisms behind simultaneous improvement of interdependent Seebeck coefficient and electrical conductivity. For this, we comprehensively studied the electronic and crystallographic structure of Na$_{0.75}$CoO$_{2}$ doped with 5 elements Mg, Sb, Zn, Ni and Eu. These elements represent wide variety of electronic configurations such as open {\it d} and {\it f} shells, closed {\it d} and {\it s} shells, combined with great variation in atomic mass. Systematic density functional calculations showed that the Ni and Zn were more stable when substituting Co with formation energy 2.35 eV, 2.08 eV. While Eu and Mg and Sb are more stable when it substitutes Na. In the case of Mg these results are consistent with Raman scattering measurement. This suggests that the doped Mg ions immobilize Na ions, reducing the resistivity by improving the mobility of carriers and thus enhancing the thermo-power. [Preview Abstract] |
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H1.00334: Fluctuations in the electron system of a superconductor exposed to a photon flux Pieter De Visser, Jochem Baselmans, Juan Bueno, Nuria Llombart, Teun Klapwijk In a superconductor, in which electrons are paired, the density of unpaired electrons should become zero when approaching zero temperature. Therefore radiation detectors based on breaking of pairs promise supreme sensitivity, which we demonstrate using an aluminium superconducting microwave resonator. We show that the resonator also enables the study of the response of the electron system of the superconductor to pair-breaking photons, microwave photons and varying temperatures. A large range in radiation power (at 1.54 THz) can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48 $\pm$ 8{\%}) and showing an unprecedented detector sensitivity. At low radiation power fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime. [Preview Abstract] |
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H1.00335: Thermal doping by vacancy formation in copper sulfide nanocrystal arrays Yehonadav Bekenstein, Kathy Vinokurov, Shay Keren-Zur, Oded Millo, Uri Banin Doping semiconductor nanocrystals (NCs) is a highly pursued challenge, providing another means, along with size and shape, for controlling their electronic properties. We present a new, impurity free, method for NC doping by thermal treatment at moderate temperatures of under 400K, thus creating vacancies leading to free charge carriers. This method is applied here for Cu$_{2}$S NCs, where Cu vacancies easily form due to the low chemical potential of Cu(0), resulting in p-type doping. This thermal doping procedure is used here to controllably increase the conductance of Cu$_{2}$S-NC arrays, achieving up to 6 orders of magnitude enhancement, for which we extract the activation energy for Cu vacancy formation, $\sim$1.6eV. The thermal doping effect manifests itself also in tunneling spectra by the emergence of in-gap states and a shift of the Fermi level towards the valance band, signifying p-type doping. In addition we demonstrated local thermal doping of the NC film via a focused laser beam, serving as the heating source, which enables fabrication of advanced NC devices. [Preview Abstract] |
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H1.00336: Perceptions of the Schrodinger equation Spyros Efthimiades The Schrodinger equation has been considered to be a postulate of quantum physics, but it is also perceived as the quantum equivalent of the non-relativistic classical energy relation. We argue that the Schrodinger equation cannot be a physical postulate, and we show explicitly that its second space derivative term is wrongly associated with the kinetic energy of the particle. The kinetic energy of a particle at a point is proportional to the square of the momentum, that is, to the square of the first space derivative of the wavefunction. Analyzing particle interactions, we realize that particles have multiple virtual motions and that each motion is accompanied by a wave that has constant amplitude. Accordingly, we define the wavefunction as the superposition of the virtual waves of the particle. In simple interaction settings we can tell what particle motions arise and can explain the outcomes in direct and tangible terms. Most importantly, the mathematical foundation of quantum mechanics becomes clear and justified, and we derive the Schrodinger, Dirac, etc. equations as the conditions the wavefunction must satisfy at each space-time point in order to fulfill the respective total energy equation. [Preview Abstract] |
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H1.00337: Synthesis and Electrochemical Characterization of Liquid Phase Exfoliated Graphene Flakes Julianna Richie, Jacob Huffstutler, Milinda Wasala, Andrew Winchester, Sujoy Ghosh, Swastik Kar, Saikat Talapatra We will present our results on synthesis and characterization of few-layer graphene nanoflakes obtained from bulk graphite in isopropanol alcohol (IPA) using Liquid-phase exfoliation technique. Results of sample characterization using ultraviolet-visible (UV-VIS) spectroscopy, transmission electron microscopy (TEM), cyclic voltammetry (CV), electrical impedance spectroscopy (EIS), and galvanostatic charge-discharge will be presented. Potential use of these materials as electric double-layer capacitor (EDLC) electrodes were investigated using 6M KOH as electrolyte. We found that these devices possess specific capacitance values as high as 23F/g at a 1 mV scan rate. Several other parameters related to the EDLC performances will be presented in detail. [Preview Abstract] |
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H1.00338: Anomalous velocity distributions in a model for active Brownian suspensions Benjamin Vollmayr-Lee, Andrea Fiege, Annette Zippelius Large scale simulations and analytical theory have been combined to obtain the non-equilibrium velocity distribution, $f(v)$, of randomly accelerated particles in suspension. The simulations are based on an event-driven algorithm, generalised to include friction. They reveal strongly anomalous but largely universal distributions which are independent of volume fraction and collision processes, which suggests a one-particle model should capture all the essential features. We have formulated this one-particle model and solved it analytically in the limit of strong damping, where we find that $f(v)$ decays as $1/v$ for multiple decades, eventually crossing over to a Gaussian decay for the largest velocities. Many particle simulations and numerical solution of the one-particle model agree for all values of the damping. [Preview Abstract] |
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H1.00339: Analysis of Optogalvanic Transients at 621.7 nm, 633.4 nm and 640.2 nm of Neon in a Discharge Plasma Fitted with a Monte Carlo Mathematical Model. Kayode Ogungbemi, Xianming Han, Micheal Blosser, Prabhakar Misra Optogalvanic transitions have been recorded and fitted for 1s$_{\mathrm{5}}$ - 2p$_{\mathrm{7\thinspace }}$(621.7 nm), 1s$_{\mathrm{5}}$ - 2p$_{\mathrm{8}}$ (633.4 nm) and 1s$_{\mathrm{5}}$ - 2p$_{\mathrm{9}}$ (640.2 nm) transitions of neon in a Fe-Ne hollow cathode plasma discharge as a function of current (2-19 mA) and time evolution (0-50 microsec). The optogalvanic waveforms have been fitted to a Monte carlo mathematical model. The variation in the excited population of neon is governed by the rate of collision of the atoms involving the common metastable state (1s$_{\mathrm{5}})$ for the three transitions investigated. The concomitant changes in amplitudes and intensities of the optogalvanic signal waveforms associated with these transitions have been studied rigorously and the fitted parameters obtained using the Monte Carlo algorithm to help better understand the physics of the hollow cathode discharge. [Preview Abstract] |
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H1.00340: Democracy is a historical urgency Miroslav Synek Survival of human society on this planet depends heavily on coping with advanced nuclear technological development. Democracy is a historical urgency, in the age of intercontinental nuclear missiles, computerized on a push-button, conceivably controllable by a miscalculating, suicidal and very powerful dictator, producing a global nuclear holocaust, on our entire planet. Diplomacy should help humanity to approach the contemporary situation. [Preview Abstract] |
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H1.00341: Characterization of electrochemically formed nanoscale dimple patterns by morphological and hexatic correlation analysis Hussain Sangji, Sherdeep Singh, Stephen Wang, Peter Kruse, Paul Wiseman We have previously described the emergence of ordered nanoscale dimple lattices by dissipative processes, which cover several $cm^2$ of the surface, during electropolishing of titanium, tungsten, zirconium and tantalum. Techniques to quantitatively characterise the properties of the surface pattern are useful for tuning the experimental parameters to generate desirable surfaces. Here we present SEM image analysis methodologies and results for the characterization of dimple patterns on Tantalum. We study morphological properties by colour coding the angular orientation of the hexagonal cells formed by the dimples with their nearest neighbours, and by labelling defects in the hexagonal lattice. We show that the morphology of the pattern is affected by the grain boundaries of the tantalum substrate and variations in its height. We also quantify the average quality of the pattern using a hexatic order parameter and spatial correlation function, and find that the quality can vary under constant electrochemical conditions according to the tantalum grain. These studies may facilitate the development of tunable self-ordered nanoscale patterns on surfaces for applications in solar cells, biocompatible materials and catalysis. [Preview Abstract] |
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H1.00342: Fitting of interatomic potentials without using force information: a parallel particle swarm optimization algorithm Diego Gonz\'alez, Sergio Davis In this work we present a methodology for fitting interatomic potentials to \emph{ab initio} data, using the particle swarm optimization (PSO) algorithm. The objective function to be minimized is the total prediction error in the energies for the configurations provided, thus the algorithm does not require any information besides the atomic positions for each configuration and their corresponding ab initio energies. In particular it does not require the atomic forces, as in other fitting procedures such as force matching methods. Our procedure has been tested by fitting both pair potentials and embedded atom potentials, up to a prediction error of the order of 10$^{-4}$ eV/atom, using only 10 different configurations. The implementation code is parallelized using message passing interface (MPI) libraries. [Preview Abstract] |
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H1.00343: \textit{In situ} resistivity of endotaxial FeSi$_{2}$ nanowires on Si(110) Peter Bennett, David Smith, Sam Tobler We present in situ UHV measurements of the resistivity of self-assembled endotaxial FeSi$_{2}$ nanowires (NWs) on Si(110) using a variable-spacing two-point method with an STM tip and a fixed contact pad. The resistivity at room temperature was found to vary with NW width with approximate values of $\rho_{\mathrm{NW}} =$ 220 $\mu \Omega $cm at 12 nm and 400 $\mu \Omega $cm at 3 nm. The increase at small W is attributed to boundary scattering, and is fit to the F-S model, yielding values of $\rho_{0} =$ 120 $\mu \Omega $cm and $\lambda $ $=$ 7 nm, for specularity parameter p $=$ 0.5. Upon partial oxidation by exposure to air, the resistivity of a 4 nm NW increased approximately 50{\%}. The resistivity is relatively insensitive to NW size or oxidation, which is attributed to a high concentration of point defects in the FeSi$_{2}$ structure, with a correspondingly short inelastic electron scattering length. It is remarkable that the defect concentration persists in very small structures. [Preview Abstract] |
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H1.00344: Adiabatic quantum state transfer in the presence of cavity shot noise Christopher Chamberland, Aashish Clerk, Bill Coish Many areas of physics rely upon adiabatic state transfer protocols, allowing a quantum state to be moved between different physical systems for storage and retrieval or state manipulation. However, these state transfer protocols suffer from dephasing and dissipation. This work goes beyond standard open-systems treatment of quantum dissipation allowing us to consider non-Markovian environments. After developing the general theoretical tools, we apply our methods to adiabatic state transfer between qubits in a driven cavity. We explicitly consider dephasing effects due to unavoidable photon shot noise. These results will be useful to ongoing experiments in circuit QED systems. [Preview Abstract] |
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H1.00345: High-quality epitaxial graphene devices with low carrier density for resistance metrology Yanfei Yang, Lung-I Huang, David Newell, Mariano Real, Randolph Elmquist Epitaxially grown graphene on silicon carbide (SiC) is a promising material for both quantum resistance metrology and wafer-scale electronics. However, monolayers are typically found to be heavily n-doped due to the charge exchange between the graphene and the non-conducting buffer layer beneath that is covalently bonded to the SiC substrate. Carrier densities are usually in the range of 10$^{12}$ $\sim$ 10$^{13}$ cm$^{-2}$, where heavy doping shifts the quantized Hall resistance plateau to high magnetic field values. Various gating methods have been developed to reduce the carrier density, but require lithography processes that increase the probability of contamination that degrades the performance of the devices. Recently, we fabricated high-quality Hall devices on diced semi-insulating SiC wafers, obtaining carrier densities in the range of 10$^{10}$ $\sim$ 10$^{11}$ cm$^{-2}$ and mobility above 10$^{4}$ cm$^{2}$V$^{-1}$s$^{-1}$ without gating. Graphene is grown on the Si face of SiC(0001) substrates and devices are fabricated using a metal layer subtractive process without organic chemical contamination of the graphene. We measure well-developed quantum Hall plateaus with filling factor $\nu =$ 2, the fingerprint for monolayer graphene, at magnetic fields below 2 T at liquid helium temperature. A variety of quantum phenomena are observed in these clean, high quality graphene devices. [Preview Abstract] |
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H1.00346: Effect of ECM Stiffness on Integrin-Ligand Binding Strength Gawain Thomas, Qi Wen Many studies have shown that cells respond to the stiffness of their extracellular matrix (ECM). However, the mechanism of this stiffness sensing is not fully understood. We believe that cells probe stiffness by applying intracellular force to the ECM via the integrin-mediated adhesions. The linkage of integrins to the cytoskeleton has been modeled as a slip clutch, which has been shown to affect focal adhesion formation and hence force transmission in a stiffness dependent manner. In contrast, the bonds between integrins and ECM have been characterized as ``catch bonds.'' It is unclear how ECM viscoelasticity affects these catch bonds. We report, for the first time, the effects of ECM stiffness on the binding strength of integrins to ECM ligands by measuring the rupture force of individual integrin-ligand bonds of cells on collagen-coated polyacrylamide gels. Results show that the integrin-collagen bonds of 3T3 fibroblasts are nearly four times stronger on a stiff (30 kPa) gel than on a soft (3 kPa) gel. The stronger integrin bonds on stiffer substrates can promote focal adhesion formation. This suggests that the substrate stiffness regulates the cell-ECM adhesions not only by affecting the cytoskeleton-integrin links but also by modulating the binding of integrins to the ECM. [Preview Abstract] |
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H1.00347: Insulator-quantum Hall transition and Dirac fermion heating in low-carrier-density monolayer epitaxial graphene Lung-I Huang, Yanfei Yang, Randolph Elmquist, David Newell, Chi-Te Liang We present magneto-transport measurements on ungated, low-carrier-density epitaxial graphene Hall devices at low temperatures $T$. At $T=$4.25 K the carrier density and mobility of one device are 1.38x10$^{11}$ cm$^{-2}$ and 6500 cm$^{2}$V$^{-1}$s$^{-1}$, respectively. At low magnetic fields $B$, this device shows insulating behavior in the sense that the measured resistivity $\rho_{\mathrm{xx}}$ increases with decreasing $T$. A highly developed quantum Hall (QH) resistivity plateau $\rho _{\mathrm{xy}}\approx \frac{h}{2e^{2}}$ corresponding to a Landau-level filling factor $\nu =$2 in monolayer graphene can be observed at magnetic fields $B\ge $ 1.5 T. Between the low-field insulator regime and the $\nu =$2 QH state we observe a $T$-independent point in $\rho _{\mathrm{xx}}$ which corresponds to the insulator-quantum Hall (I-QH) transition. This transition, like those in semiconductor-based two-dimensional (2D) systems, can be also observed by increasing the driving current $I$ at fixed ambient temperature. However, the measured $\rho _{\mathrm{xx}}$ at the I-QH transition is close to $\frac{h}{4e^{2}}$, rather than $\frac{h}{2e^{2}}$as expected by conventional I-QH theory. Furthermore, $\rho_{\mathrm{xx}}$ is substantially higher than $\rho _{\mathrm{xy}}$ at the crossing point. By using the zero-field resistivity and weak localization effect as two independent thermometers to determine effective Dirac fermion temperature ($T_{DF})$ at various $I$, we find that $T_{DF}$ $\sim$ $I^{0.5}$, consistent with those obtained in various 2D systems. [Preview Abstract] |
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H1.00348: Photoluminescence Analysis of Electron Irradiated AlGaN/GaN HEMT structures with Variation of Silicon Nitride Passivation Thickness H. Jackson, Robert Hengehold A passivation layer of silicon nitride on AlGaN$\backslash $GaN heterojunction devices can improve performance by reducing electron traps at the surface. In this study, the effects of passivation layer thickness was investigated at various thicknesses (0, 200, 500 and 1200 Angstroms) on AlGaN$\backslash $AlN$\backslash $GaN structures. 1.0 MeV Electron irradiations at a fluence of 10$^{16\, }$cm$^{-2}$ were used to increase the electron trapping at the interface as well as examine the impact on transport and thus ascertain the quality of the interface. Additionally, pre- and post-irradiation photoluminescence spectroscopy was used to reveal near-band-edge shallow electron donors, neutral donor bound excitons (D$^{0\, \, }$X$_{A\, })$ as well as deep center yellow/blue bands. Correlation of the post radiation spectra will be made to other device characteristics as a function of Silicon Nitride passivation thickness. [Preview Abstract] |
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H1.00349: Quantum correlations beyond Tsirelson's bound Dominic Berry, Martin Ringbauer, Alessandro Fedrizzi, Andrew White Violations of Bell inequalities show that there are correlations that cannot explained by any classical theory. Further violation, beyond Tsirelson's bound, shows that there are correlations that are not explained by quantum mechanics. Such super-quantum correlations would enable violation of information causality, where communication of one bit provides more than one bit of information [Nature 461, 1101 (2009)]. An unavoidable feature of all realistic Bell inequality experiments is loss. If one postselects on successful measurements, unentangled states can violate Bell inequalities. On the other hand, loss can be used to enhance the violation of Bell inequalities for entangled states. This can improve the ability to distinguish between entangled and unentangled states, despite loss. Here we report an optical experiment providing maximal violation of the CHSH-Bell inequality with entangled states. Due to loss and postselection, Tsirelson's bound is also violated. This enables us to more easily distinguish between entangled and unentangled states. In addition, it provides violation of information causality for the postselected data. [Preview Abstract] |
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H1.00350: Hyperfine Interactions for Hole Spins in Quantum Dots Pericles Philippoppoulos, Sefano Chesi, William Coish Due to the anisotropic nature of the hyperfine coupling for hole spins in semiconductor quantum dots, these systems may show significantly longer coherence times than electron spins given the correct quantum-dot geometry and magnetic field orientation. This advantage of hole spins relies on the hyperfine tensor taking-on an Ising-like form. This form of the hyperfine coupling has been recently called into question with experiments [1] that have been interpreted to indicate a strong hybridization of p-like and d-like components in the valence band of III-V semiconductors. However, this interpretation relies on two assumptions: (1) That spin-orbit coupling is weak in these systems compared to the anisotropic crystal field, and (2) that higher-angular-momentum contributions are negligible. Assumption (1) may break down in light of the fact that the spin-orbit energy is even larger than the principle gap in InAs, and assumption (2) is difficult to justify in any crystal that breaks pure rotational symmetry. Using a generalization of the group-theoretic analysis in [1], we show here that relaxing either of these assumptions can restore the Ising-like nature of the hyperfine tensor, albeit for a particular choice of coupling constants. \\[4pt] [1] E. A. Chekhovich et al. Nature Physics, 2012 [Preview Abstract] |
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H1.00351: Fabrication of Electronic Fabry-Perot Interferometer in the Quantum Hall Regime Simas Glinskis, Sanghun An, Woowon Kang, Leo Ocola, Loren Pfeiffer, Ken West, Kirk Baldwin A fabrication method for electronic quantum Hall Fabry-Perot interferometers (FPI) is presented. Our method uses a combination of e-beam lithography and low-damage dry-etching to minimize creation of charged traps and deposition of impurities in the FPI devices. Optimization of the quantum point contacts (QPC) is achieved via systematically varying the etch depth and monitoring the device resistance after each etch session. Etching of the device is stopped and gates are metallized when a desired value of resistance is obtained. This helps to ensure that the QPCs are neither insulating (etched too deep) nor too conductive (etched too shallow). The target values for device resistance at the end of the etching procedure are determined using the statistics of resistance values compiled from all the previous FPI devices fabricated from the same wafer. Our approach allows for a systematic tuning of the QPC potentials so that the strength of quantum interference signal can be optimized. [Preview Abstract] |
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H1.00352: Significantly Better Than Expected Sensitivity in Chemotactic Response by a Model Unicellular Eukaryote Carl Franck, Igor Segota Recently we demonstrated (Segota et al., J.R. Soc. Interface v. 10, 20130606 (2013)) that the conventional wisdom of what determines the signal to noise ratio in chemotaxis for the unicellular eukaryote, Dictyostelium discoideum is apparently fundamentally flawed. In our poster we will review the evidence and point to appropriate next steps in both experiment and theory. [Preview Abstract] |
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H1.00353: Superfluid Optomechanics Glen Harris, David McAuslan, Eoin Sheridan, Warwick Bowen The field of quantum optomechanics has seen great progress over the last decade with many exciting theoretical proposals and impressive experimental achievements. Among the most successful optomechanical systems are the collective modes of ultra cold atoms where ponderomotive squeezing and quantization of collective atomic motion have been observed. In this context the collective motion of superfluid helium-4 appears to be a promising candidate given its zero viscosity flow; potentially leading to the simple preparation of macroscopic mechanical oscillators with ultra-high quality factors. Here we present the first observation of Brownian motion in superfluid helium-4 thin films. The superfluid film is formed around an optical whispering gallery mode resonator enabling high sensitivity readout. Furthermore, exceedingly strong dynamical backaction heating and cooling is observed with optomechanical instabilities arising from only 40nW of injected optical power. While there are still many open questions regarding the superfluid hydrodynamics we believe this to be a promising system to study macroscopic non-classical mechanical states. [Preview Abstract] |
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H1.00354: Micro Structure of Nickel in Spin Coated Thin Film Magnets Katherine Vides, Rasika Dahanayake, Pubudu Samarasekara, Sunil Dehipawala Micro-Structure of Nickel compounds in thin film magnets was investigated using Extended X ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES). These thin film magnets were prepared by spin coating several layers of precursor containing iron and Nickel on a glass substrate. Thickness of the films was controlled by spin rate. Several magnets were prepared with different thicknesses and each film was annealed to either 200C or 350c in air. Variation of oxidation state and nearest neighbor bond lengths of each magnet was measured to characterize Ni in the film. [Preview Abstract] |
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H1.00355: A Molecular Dynamics Simulation of the Density Fluctuation in the Diatomic Fluids around the Critical Points Shohei Ikawa, Takashi Tokumasu, Nobuyuki Tsuboi, Shinichi Tsuda In this study, we investigated the principle of corresponding state on the density fluctuation around the critical points of non-polar diatomic fluids. We performed the Molecular Dynamics (MD) simulation for the extraction of the fluctuation structure around the critical points of 2-Center-Lennard-Jones (2CLJ) fluids, which have anisotropy depending on the molecular elongations. We estimated the fluctuation structure by two methods. One is the evaluation of the dispersion of the number of molecules at a certain domain, and the other is the calculation of static structure factor. As a result, in 2CLJ fluids that have shorter molecular elongations comparatively, the principle of corresponding state is satisfied because of the small differences in the fluctuation structure extracted in the present two methods. In addition, paying attention to the time variation of the density fluctuation, we confirmed that the characteristic frequency of the fluctuation is clearly lower around the critical point compared with the other conditions. Hereafter, we are going to calculate a dynamic structure factor, further investigating the principle of corresponding state of density fluctuation. [Preview Abstract] |
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H1.00356: Partial heating between counter propagating quantum Hall edge channels Kazuhisa Washio, Ryo Nakazawa, Masayuki Hashisaka, Koji Muraki, Toshimasa Fujisawa In contrast to clear unidirectional charge flow in quantum Hall edge channels, heat transport and equilibration remain veiled. Most of the previous works were concentrated on heating between co-propagating edge channels, where co-propagating charge and spin modes are formed by the Coulomb interaction [1]. Here, we investigate heating between counter propagating edge channels separated by a narrow surface gate of the width 0.1 $\mu$m, where the plasmon coupling forms counter-propagating dragging modes [2]. One edge channel is directly heated up by a quantum point contact at its half transmission, and energy spectrum of the other edge channel is evaluated by quantum dot thermometry. We observed partial heating in the spectrum, where a small fraction (1-5 percent) of electrons is highly excited over the original Fermi distribution, for an interaction length of 5-10 $\mu$m in the coupled channels. This can be understood by considering weak scattering process between the channels. The flow of this non-equilibrium distribution will be discussed with different configurations of heating and detecting channels in terms of the chirality and the dragging modes.\\[4pt] [1] H. le Sueur el al., PRL 105, 056803 (2010)\\[0pt] [2] H. Kamata et al., to be published. (cond-mat/1309.7471) [Preview Abstract] |
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H1.00357: Boundary Condtions of Gravity Shantilal Goradia Our quantum mechanical derivation of the strong coupling using modified Newtonian inverse square logic in (1) and the fine structure constant (ALPHA) using Boltzmann expression in our book (2) come close to Einstein's 1919 paper merging nuclear force with gravitation and retracting his cosmological constant. Its conflict with the inflationary aspect of the universe can be reconciled with the possibility that the light coming from the receding galaxies follow a curvilinear path increasing in length due to its ever increasing curvature without receding only in the radial direction. In (1), we implicitly show gravity as nothing but the cumulative effect of quantum mechanical forces, making G vary at different locations in the universe. The subsequent effects of gravitational variation would be on the curvature of the paths of the geodesics they create. Further investigation along these lines is warranted as we do not have unification, evidence of graviton, quantum gravity or anything else very concrete after a century of hard work. Strong coupling and ALPHA may be the boundary conditions of gravitational constants.\\[4pt] [1] Newtonian Gravity in Natural Units, Journal of Physical Science and Application 2 (7) (2012)265-268.\\[0pt] [2] Quantum Consciousness - The Road to Reality. [Preview Abstract] |
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H1.00358: Quadratic Measurement and Conditional State Preparation in an Optomechanical System George Brawley, Michael Vanner, Warwick Bowen, Silvan Schmid, Anja Boisen An important requirement in the study of quantum systems is the ability to measure non-linear observables at the level of quantum fluctuations. Such measurements enable the conditional preparation of highly non-classical states. Nonlinear measurement, although achieved in a variety of quantum systems including microwave cavity modes and optical fields, remains an outstanding problem in both electromechanical and optomechanical systems. To the best of our knowledge, previous experimental efforts to achieve nonlinear measurement of mechanical motion have not yielded strong coupling, nor the observation of quadratic mechanical motion. Here using a new technique reliant on the intrinsic nonlinearity of the optomechanical interaction, we experimentally observe for the first time a position squared ($x^2$) measurement of the room-temperature Brownian motion of a nanomechanical oscillator. We utilize this measurement to conditionally prepare non-Gaussian bimodal states, which are the high temperature classical analogue of quantum macroscopic superposition states, or cat states. In the future with the aid of cryogenics and state-of-the-art optical cavities, our approach will provide a viable method of generating quantum superposition states of mechanical oscillators. [Preview Abstract] |
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H1.00359: ABSTRACT WITHDRAWN |
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H1.00360: Graphene Quantum Point Contact Transistor for DNA Sensing Anuj Girdhar Over the past few years the need has grown for low-cost, high-speed, and accurate biomolecule sensing technology. Graphene is a promising choice for use in such sensing applications, as its single-atom thickness and unique electronic structure is suitable for probing biomolecules like DNA at a very high resolution. We propose the design of a transistor containing a graphene nanoribbon sensing layer with a nanopore for the simultaneous detection and control of a translocating DNA molecule. Through the combination of molecular dynamics simulations, a self-consistent Poisson equation solver, and electronic transport theory, we show that the motion of a DNA molecule through a nanopore can be observed by measuring conductance modulations in the graphene nanoribbon. We also demonstrate that the sensitivity of the graphene sheet conductance to external charges can be enhanced by modulating its carrier concentration as well as by choosing a quantum point contact geometry for the graphene nanoribbon. In addition, we propose the use of extra gates to control both the lateral and translocating motion of a DNA molecule inside the nanopore. [Preview Abstract] |
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H1.00361: ABSTRACT WITHDRAWN |
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H1.00362: A multiphase equation of state for BeO based on the modified mean-field potential approach Hai-Feng Song, Ming-Feng Tian We present a first-principles scheme to study the multiphase equation of state (EOS) for BeO, based on the modified mean-field potential (MMFP) approach. We first calculate the EOS for BeO of hexagonal wurtzite and rocksalt structure, and then compute the melting curve of BeO by using MMFP approach. At last, based on the EOS of hexagonal wurtzite BeO and melting curve and considing the effcet of the melting entropy, we obtain the EOS of liquid BeO. Based on the results, we obtain the multiphase EOS of BeO and a phase diagram. The calcutlated Hugoiot is in agreement with available experimental data. [Preview Abstract] |
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H1.00363: Semiempirical multi-phase Equation of state of Al Gongmu Zhang, Hai-Feng Liu Equation of state (EOS) is the fundamental characteristic of matter determining its thermodynamic properties over a wide range of the phase diagram. EOS are based on a three-term Helmholtz free energy, given as a function of the specific volume V and temperature T. Semiempirical EOS use with great efficiency results obtained by theories and experimental data. Al serves as a standard material for high pressure region ,the EOS for this metal need to be especially exact and reliable. We construct the EOS for Al can describe the phase solid, liquid and gas, it agrees with IEX and DAC experiment data and the other theories data well. [Preview Abstract] |
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H1.00364: Vectorization for Molecular Dynamics on Intel Xeon Phi Corpocessors Hongsuk Yi Many modern processors are capable of exploiting data-level parallelism through the use of single instruction multiple data (SIMD) execution. The new Intel Xeon Phi coprocessor supports 512 bit vector registers for the high performance computing. In this paper, we have developed a hierarchical parallelization scheme for accelerated molecular dynamics simulations with the Terfoff potentials for covalent bond solid crystals on Intel Xeon Phi coprocessor systems. The scheme exploits multi-level parallelism computing. We combine thread-level parallelism using a tightly coupled thread-level and task-level parallelism with 512-bit vector register. The simulation results show that the parallel performance of SIMD implementations on Xeon Phi is apparently superior to their x86 CPU architecture. [Preview Abstract] |
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H1.00365: Influence of Molecular Size on the Density-Functional Delocalization Error Sarah Whittleton, Alberto Otero-de-la-Roza, Erin Johnson While density-functional theory (DFT) is an effective and popular method in quantum chemistry and physics, approximations within the exchange-correlation functional can produce substantial inaccuracies. For example the local density approximation (LDA) and generalized-gradient approximation (GGA) produce convex energy versus charge curves that violate the correct piecewise-linearity constraint of $E(N)$ for fractional charges, referred to as delocalization error. This leads to a false description of molecular properties, such as the HOMO and LUMO energy levels. This work investigates the delocalization error in a series of gas-phase organic molecules including alkanes, alkenes, alkynes, allenes, and polycyclic aromatic hydrocarbons. The GGA deviation from linearity of the $E(N)$ curves is evaluated and $\omega$-tuning of a long-range corrected functional is performed for each molecule. It is found that the deviation from linearity and thus the optimal $\omega$, decrease with increasing molecular size. However, systematic error in the endpoint of the $E(N)$ curve, and thus in the ionization potential, is simultaneously introduced, demonstrating the impact of molecular size on delocalization error. [Preview Abstract] |
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H1.00366: ABSTRACT WITHDRAWN |
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H1.00367: Development of Tuning Fork Based Probes for Atomic Force Microscopy Romaneh Jalilian, Mehdi M Yazdanpanah, Neil Torrez, Amirali Alizadeh, Davood Askari This article reports on the development of tuning fork-based AFM/STM probes in NaugaNeedles LLC for use in atomic force microscopy. These probes can be mounted on different carriers per customers' request. (e.g., RHK carrier, Omicron carrier, and tuning fork on a Sapphire disk). We are able to design and engineer tuning forks on any type of carrier used in the market. We can attach three types of tips on the edge of a tuning fork prong (i.e., growing Ag$_{2}$Ga nanoneedles at any arbitrary angle, cantilever of AFM tip, and tungsten wire) with lengths from 100-500 $\mu $m. The nanoneedle is located vertical to the fork. Using a suitable insulation and metallic coating, we can make QPlus sensors that can detect tunneling current during the AFM scan. To make Qplus sensors, the entire quartz fork will be coated with an insulating material, before attaching the nanoneedle. Then, the top edge of one prong is coated with a thin layer of conductive metal and the nanoneedle is attached to the fork end of the metal coated prong. The metal coating provides electrical connection to the tip for tunneling current readout and to the electrodes and used to read the QPlus current. Since the amount of mass added to the fork is minimal, the resonance frequency spectrum does not change and still remains around 32.6 KHz and the Q factor is around 1,200 in ambient condition. These probes can enhance the performance of tuning fork based atomic microscopy. [Preview Abstract] |
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H1.00368: Comparative study of Density Functionals for Calculation of Core Electron Binding Energies in First-row Hydrides and Glycine Iogann Tolbatov, Daniel Chipman In our study we use the $\Delta $SCF approach and a wide variety of pure and hybrid density functional approaches to study CEBEs in glycine, methane, ammonia, and water. We focus on establishing methods having potential to improve analysis of experimental X-ray photoelectron spectra of amino acids, DNA nucleosides, and large polypeptides in various environments. Several well performing density functionals are found that can reproduce experimental results within 0.2 eV on average for the absolute binding energies and also for the intramolecular and intermolecular shifts in the studied molecules. Accuracy in each approach is evaluated in reproducing experimental values for the absolute CEBEs in all four molecules and for the intramolecular and intermolecular chemical shifts between like nuclei in the same or different molecules. Promising candidates that we have found are recommended for future analysis due to their accuracy and efficiency in computation of CEBEs and chemical shifts. [Preview Abstract] |
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