Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session V1: Poster Session III (1:00 - 4:00PM) |
Hide Abstracts |
Room: Exhibit Hall EF |
|
V1.00001: CLIMATE PHYSICS |
|
V1.00002: Blowpipe Mineralogy for Physics/Environment: Highest-Possible-Tc SuperConductor (Beyond: (but via!!!) MgB2, Cuprates, Pnictides) Quest; BOTH PERMANENT FOREVER Carb-IDES SOLID-State Sequestration AND Drought(s)-Elimination Kurt Segler, Wendell Williams, Edward Siegel Detailed are old blowpipe new applications: charcoal-block reduction of borates to yield ("N-NW" of MgB2) Overhauser-[PR 35,1,411(1987); Intl.J.Mod.Phys.1, 2 {\&} 4, 927(1987)]-"land" predicted high-EST-POSSIBLE Tc SC \~{ } "LiD2"; very-early: Siegel[Phys.Stat.Sol.(a)11,45(1972);Semiconductors.and Insulators 5: 39,47,62(1979)] carb-IDES SOLID-state phase-TRANSITIONED CHEMICALLY-REDOX"-REACTED STABLE PERMANENT LONG-term NOT "CO2"/''CH4'' BUT C-sequestration: PROFITABLE "Grab and Sell" TRUMPS "cap and trade"!!!; Mott alloying/vertical metal-insulator transitions in "borax-(GLASS)-beads"; and very-early Siegel [3rd Intl.Conf.Alt.Energy (1980)-vol.5/p.459!!!] "FLYING-WATER" Hindenberg-effect (H2-UP;H2O-DOWN) via Hydrogen-maximal-Archimedes-buoyancy "chemical-rain-in-pipelines", only via Siegel DIFFUSIVE-MAGNETO-RESISTANCE(D-MR) proprietary "magnetic-hydrogen-valve"(MHV): Renewables-Hydrogen-Water flexible versatile agile scaleable retrofitable integrated operating-system for PERMANENT drought(s)-elimination FOREVER!!! [Preview Abstract] |
|
V1.00003: FLYING-WATER Renewables-H2-H2O TERRAFORMING: PERMANENT ETERNAL Drought(s)-Elimination FOREVER!!! J. Wignall, Marv Lyons, G. Ertl, Georg Alefeld, W. Youdelis, H. Radd, G. Oertle, Edward Siegel "H2O H2O everywhere; ne'er a drop to drink"[Coleridge(1798)]; now: "H2 H2 everywhere; STILL ne'er a drop to drink": ONLY H2 (or methane CH4) can be FLYING-WATER(F-W) chemical-rain-in-pipelines Hindenberg-effect (H2-UP;H2O-DOWN): \textbraceleft $\backslash $\textbraceleft \textbraceright O/H2O\textbraceleft $\backslash $\textbraceright \textbraceright $=$[16]/[18] {\$}$\backslash $sim {\$}90\textbraceleft $\backslash ${\%}\textbraceright ; O already in air uphill; NO H2O pumping need! In global-warming driven H2O-starved glacial-melting world, rescue is possible ONLY by Siegel [$\backslash $underline \textbraceleft 3rd Intl. Conf. Alt.-Energy \textbraceright (1980)-vol.5/p.459!!!] Renewables-H2-H2O purposely flexible versatile agile customizable scaleable retrofitable integrated operating-system. Rosenfeld[Science 315,1396(3/9/2007)]-Biello [Sci.Am .(3/9 /2007)] crucial geomorphology which ONLY maximal-buoyancy H2 can exploit, to again make "Mountains into Fountains", ``upthrust rocks trapping the clouds to precipitate their rain/snow/H2O'': "terraforming"(and ocean-rebasificaton!!!) ONLY VIA Siegel[APS March MTGS.:1960s-2000ss) DIFFUSIVE-MAGNETORESISTANCE (DMR) proprietary MAGNETIC-HYDROGEN-VALVE(MHV) ALL-IMPORTANT PRECLUDED RADIAL-diffusion, permitting ONLY AXIAL-H2-BALLISTIC-flow (``G.A''.''/DoE''/''Terrapower''/''Intellectual-Ventures''/ ''Gileland''/ ''Myhrvold''/''Gates'' ``ARCHIMEDES'') in ALREADY IN-ground dense BCC/ferritic-steels pipelines-network (NO new infrastructure) counters Tromp[Science 300,1740(2003)] dire warning of global-pandemics (cancers/ blindness/ famine) [Preview Abstract] |
|
V1.00004: Examining Stratocumulus Properties over the Southeast Pacific Isabel McCoy, Andreas Muhlbauer, Robert Wood Variability in Stratocumulus (Sc) clouds is important to the planetary albedo and radiation budget because of the resulting range in reflection of incoming shortwave radiation back to space, thereby cooling the atmosphere differently. Understanding more of their micro and macro physical properties is essential to reduce uncertainty in global climate model prediction and add confidence in future climate predictions. Sc clouds have been characterized into four main categories based on their morphology and level of mesoscale organization (Wood and Hartmann, 2006). Working with satellite data from NASA's CloudSat and Goes 10 in combination with these occurrence identifications, we developed statistics on the microphysical characteristics for each cloud type. Comparisons are drawn between our results and aircraft data sampling the region of interest (the VOCALS Regional Experiment over the Southeast Pacific in 2008). We conclude that this is a feasible method of characterizing satellite data to derive pertinent results about Sc clouds. [Preview Abstract] |
|
V1.00005: Man-Made ``Global Warming/Climate Change'': A Critical Analysis of some of the Scientific and Methodological Approaches Laurence I. Gould Many arguments have been made that -- as a result of human activities which emit greenhouse gases (mainly carbon dioxide) -- there is a trend of increasing global temperatures so as to result in such physical events as melting glaciers, rising sea levels, and increased storms. This presentation will examine some of the arguments given for such a trend in the light of corresponding counter-arguments [1]. \\[4pt] [1] The 2011 Interim Report from the Nongovernmental International Panel on Climate Change -- http://www.nipccreport.org/reports/2011/2011report.html (most of the research reported here appears in peer-reviewed science journals) [Preview Abstract] |
|
V1.00006: METALS AND METALLICS ALLOYS |
|
V1.00007: Atomistic analysis of short range interaction and local chemical order in LPSO structures of Magnesium alloys Marco Fronzi, Hajime Kimizuka, Kazuki Matsubara, Shigenobu Ogata Magnesium alloys have been object of interest as lightweight material with high strength weight ratio. In particular Long Period Stacking Ordered (LPSO) structure phases show to have a strong influence in enhancing mechanical properties of such kind alloys. However the chemical order of the interacting atomic species in the Mg lattice has not been fully understood. We perform first principles Density Functional Theory (DFT) calculation to compute formation energies as well as interaction energies of the doping atoms in both Faced Centered Cubic (FCC) and Hexagonal Close Packed (HCP) Mg lattices. In particular we consider the Mg-Al-Gd and Mg-Zn-Y ternary systems. We also calculate activation energies for vacancy assisted doping atoms diffusion in order to perform a further analysis of the kinetics of the process. In order to describe short range interaction and cluster formation in the Mg matrix, we build an on lattice potential based on first principles DFT interaction energies. By means of these inter-atomic potentials, we perform Monte Carlo simulations to analyze the chemical order occurring in LPSO Mg-Al-Gd structures. [Preview Abstract] |
|
V1.00008: Measurement of semi-rigid coaxial cables at cryogenic temperature -thermal conductance and attenuation- Soichi Kasai, Akihiro Kushino We are developing semi-rigid coaxial cables for low temperature experiments which require fast readout with low noise. Coaxial cables used at low temperature are made of low thermal conductivity materials, such as stainless-steel, cupro-nickel and polytetrafluoroethylene to suppress heat penetration through cables. As the thermal conductivity of such alloys is affected by the thermal and mechanical treatment in forming process, we have to measure thermal property of coaxial cables after forming. The low thermal conductance of 5.5 cm specimen was measured by the steady-state heat-flow method with 1m long and thin niobium-titanium wiring for thermometers and heaters. Signal attenuation of coaxial cables was measured at 3K stage of an adiabatic demagnetization refrigerator. In order to cool center electrical conductor, the cables with 1m long length were coiled, and surrounded by copper blocks then attached to 3K stage. We successfully observed superconducting transition of center conductor of superconducting niobium-titanium coaxial cables with this method. [Preview Abstract] |
|
V1.00009: Analytical Expression for a Pseudo-Potential in Alkali Metals Gregorio Ruiz-Chavarria In previous works [1-3] using a local first principles pseudo-potential, have been calculated inter-ionic potential and thereafter different properties have been obtained from simple metals as phonon dispersion curves, phonon spectra, specific heats properly. The pseudo-potential is constructed from the electron density, which is previously calculated by the density functional theory. All this process is carried out numerically. The pseudo-potential has a similar behavior in the alkali metals and then we propose an analytical expression for it, which depends on the parameter rs, the atomic number and two additional parameters. This analytical pseudo-potential is used to calculated phonon dispersion curves, which are in good agreement with existing experimental reports, it is expected that the other properties calculated based on this pseudo-pontencial match with the experimental results.\\[4pt] [1] Manninen M., et al, Phys.Rev. B 24 (1981) 7057\\[0pt] [2] Ruiz, G., Physics Letters A 336 (2005) 210\\[0pt] [3] Maga\~na,L.F. and V\'azquez, G.J., Phys.Rev.B 36 (1987) 4700 [Preview Abstract] |
|
V1.00010: Measurement of Optical, Mechanical and Transport properties of the hexagonal closed packed 4H polytype of metallic silver Indrani Chakraborty, Sharmila N. Shirodkar, Smita Gohil, Umesh Waghmare, Pushan Ayyub Optical, mechanical and transport property measurements were done on the hexagonal closed packed (hcp) 4H polytype of Ag with stacking sequence ABCBABCB.. grown as bulk films on $Al_{2}O_{3}$ substrates. Diffused reflectance measurements done on the 4H films showed a general loss of reflectivity amounting to a decrease of 35\% as compared to normal fcc (3C) Ag near 500 nm with a blueshift of 5nm in the bulk plasmon frequency, possibly due to the modified electronic structure of the hcp form. Raman spectroscopic measurements showed the appearance of a peak at 64.3 cm$^{-1}$ at 4K which underwent ``Mode softening,'' that is shifted to lower wave numbers with increase of temperature and disappeared above 350K. Low temperature transport measurements done on 4H films gave the in-plane resistivity value to be 39 times higher than that of a similarly synthesized fcc Ag film at 295 K. Vicker's microhardness measurements done on the 4H films showed that the 4H samples to be almost 5 times harder than the 3C Ag. Density functional theory simulations were done to obtain the phonon dispersion, band structure and nature of Fermi surface for the 4H Ag which corroborated with the experimental observations. The 4H form appears to be a much less metallic, darker and harder form of Ag. [Preview Abstract] |
|
V1.00011: Molecular Dynamics Simulation Of The Energetic Reaction Between Ni And Al Nanoparticle Aggregates Jacob Sparks, Takumi Hawa Molecular Dynamics simulations are used to simulate the energetic reaction of Ni and Al particles at the nanometer scale. The effect of particle size and structures on reaction time and temperature for Ni and Al separate nanoparticles has been considered. The differences in melting temperature and phase change behavior between Al and Ni are expected to produce differing results for the nanoparticle aggregates systems. Simulation results show that the sintering time increases with increasing mass of the aggregates and with decreasing the fractal dimension of the aggregate. The final temperature of the systems increases with decreasing the primary particle sizes when mass of the aggregates remains unchanged. The phenomenological model is a power law including a dependence on the number of particles in an aggregates and fractal dimension is also developed. [Preview Abstract] |
|
V1.00012: Electronic structure and high-temperature lattice dynamics of B2-ordered FeTi Jorge Munoz, Lisa Mauger, Matthew Lucas, Brent Fultz FeTi is a brittle, non-magnetic B2-ordered (CsCl-type) intermetallic alloy with an electronic structure similar to that of Cr. The Fermi level lays in a deep pseudo-gap and therefore, the bonding and anti-bonding orbitals are well separated. Inelastic neutron and x-ray scattering were used to measure the phonon spectra at temperatures up to 1035 K. Complementary measurements up to pressures of 47 GPa were used to obtain quasi-harmonic Gr\"{u}neisen parameters. Ab-initio calculations of the force constants and Born-von K\'{a}rm\'{a}n fits to the data show that the bonds between second nearest neighbors are much stiffer than that those between first nearest neighbors, but the rate of softening with temperature is higher for the second nearest neighbors. A comparison with the high-pressure data shows this softening to be anharmonic. A simple model relating the symmetry of the orbitals to that of the crystal structure is presented to explain the stiffness of the bonds between second nearest neighbors, while the decrease in the asphericity of the orbitals due to thermal electronic excitations is used to explain the discrepancy in the rate of softening with temperature. [Preview Abstract] |
|
V1.00013: COMPLEX STRUCTURED MATERIALS, INCLUDING GRAPHENE |
|
V1.00014: Electric-field-dependent plasmons in AA-stacked bilayer graphene Ying-Chih Chuang, Jhao-Ying Wu, Ming-Fa Lin The collective excitations in AA-stacked bilayer graphene for a perpendicular electric field are investigated analytically within the tight-binding model and the random-phase approximation. Such a field destroys the uniform probability distribution of the four sublattices. This drives a symmetry breaking between the intralayer and interlayer polarization intensities in the intrapair band excitations. A field-induced acoustic plasmon thus emerges in addition to the strongly field-tunable intrinsic acoustic and optical plasmons. At long wavelengths, the three modes show different dispersions and field dependence. The definite physical mechanism of the electrically inducible and tunable mode can be expected to also be present in other AA-stacked few-layer graphenes. [Preview Abstract] |
|
V1.00015: Radicals in Graphene Oxide: Formation and Relaxation Properties Donald Hirsh, Lyle Nolasco, Michele Vittadello, Kamil Woronowicz, Manish Chhowalla Unpaired electron spins are observed in both graphene and graphene oxide but their origins remain uncertain. We apply electron paramagnetic resonance (EPR) spectroscopy to the study of graphene oxide produced by modified Hummer's method. A narrow radical signal easily saturated at cryogenic temperatures is observed. Treatment of graphene oxide with mild reductant results in the production of additional radicals of the same linewidth and g-value. We propose that radicals are generated when epoxide rings adjacent to graphene islands open through one-electron reduction and provide preliminary data in support of this claim. The EPR spectra and relaxation properties of graphene oxide in the solid-state and dispersed in water are also compared. This comparison suggests the presence of exchange coupling between radicals on adjacent graphene oxide particles in the solid state. [Preview Abstract] |
|
V1.00016: Plasmonic heat transfer between graphene and dielectric substrate Dan You, Slava V. Rotkin This work focuses on the near-field heat transfer between graphene monolayer and a dielectric substrate by taking into account the coupling of the surface plasmon- and phonon-polaritons in graphene and in the substrate respectively. The surface plasmon and phonon polaritons are coupled to the bulk optical phonons in the substrate and in graphene that constitute thermal reservoirs, to which the surface modes are strongly coupled. We assume that the reservoirs are large and have a short relaxation time scale. The surface modes are affected by coupling to reservoir, and their energy is irreversibly dissipated into the reservoir. The frequency-dependent relaxation rate of the surface plasmon and phonon polaritons is further derived within the nonequilibrium Green's function method. Finally the calculation of the heat conductance between graphene and substrate is presented. [Preview Abstract] |
|
V1.00017: Synthesis of phosphorous-doped graphene by ambient pressure chemical vapor deposition Anupama Ghosh, Ruitao Lv, Nestor Perera Lopez, Ayse Berkdemir, Ana Laura El\'Ias, Humberto Terrones, Mauricio Terrones Although theoretical calculations have demonstrated that phosphorous (P) doping of graphene could open the largest band gap and could possess excellent properties to become an ideal toxic gas sensor, it has not been synthesized experimentally. We have successfully synthesized large-area, monolayered P-doped graphene by an ambient pressure chemical vapor deposition (AP-CVD). In particular, triphenyl phosphene (TPP) dissolved in hexane with different concentrations of TPP has been used as phosphorous-carbon precursor. Raman spectroscopy is used extensively for characterizing the different synthesized materials. The intensity ratio of D, D', 2D and G bands and their associated shifts provide information related the nature and doping levels. The strong D-band and a prominent D'-band confirms the occurrence of doping by P-substitution. The doped graphene sheets have also been characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). In addition, results on the use of these P-doped graphene in molecular sensing will be discussed. [Preview Abstract] |
|
V1.00018: Adsorption of ammonium on a pyridine-like nitrogen-doped graphene layer decorated with a monovalent atom Luis Fernando Magana, Juan M. Ramirez, Gerardo Jorge Vazquez Density functional theory and molecular dynamics were used to study the interaction of an NH$_{4}$ molecule with a pyridine-like nitrogen-doped (PNG) surface. The surface is decorated with an impurity taken from the first row of the periodic table. In this way, we considered six different atoms: H, Li, Na, K, Rb and Cs, to decorate the system. We found two final configurations. One, is with the NH$_{4}$ molecule physisorbed around the impurity. In the second situation, one hydrogen atom of the ammonium molecule, is adsorbed around a nitrogen atom of the surface. The remaining NH$_{3}$ molecule stays physisorbed on the system. The final configuration depends on the initial position of the NH$_{4}$ molecule. In all decoration cases, the system was allowed to follow an evolutionary process using molecular dynamics at 300 K, and atmospheric pressure. [Preview Abstract] |
|
V1.00019: Interaction of ammonium with a pyridine-like nitrogen-doped graphene (PNG) surface Luis Fernando Magana, Juan M. Ramirez, Gerardo Jorge Vazquez We used density functional theory, with the local density approximation, and molecular dynamics, within the Born-Oppenheimer approximation. We considered the initial position of ammonium just above the PNG vacancy, at 300 K. We performed our calculations using the Quantum Espresso code. The unit cell we considered has one vacancy per twenty-eight carbon atoms, with three nitrogen atoms, and one ammonium molecule. It is found that the PNG vacancy adsorbed strongly one hydrogen atom from the ammonium molecule. Afterwards, the remaining ammonia molecule desorbs. [Preview Abstract] |
|
V1.00020: Cracking Large-Area Gragphene into Controlled Patterns Xuanhe Zhao Fracture of single atomic layers, especially graphene, has attracted increasing interests in physics and engineering over recent years. While existing studies are mainly focused on cases with individual cracks, fracture patterns in single atomic layers have been rarely explored. Here, we present a combined experimental and theoretical study on fracture and fragmentation of single-atomic-layer graphene on substrates. Our \textit{in situ} observations show that deforming the substrates can crack large-area graphene films into patterns of long ribbons and rectangular fragments with controlled sizes. We use the shear-sliding theory to characterize the stress and deformation of graphene on substrates and carry out Monte Carlo simulations of the fragmentation process. The theoretical model matches consistently with experimental results. Our study further provides a simple method to obtain large amounts of data for statistical strengths of graphene and graphene-polymer interfaces. These properties are of fundamental importance to graphene-based materials and devices, yet extremely challenging to be measured with existing methods. [Preview Abstract] |
|
V1.00021: Anisotropic etching effect in graphene for its nanostructure engineering and defect detection Rong Yang, Zhiwen Shi, Shuang Wu, Dongxia Shi, Guangyu Zhang We report a highly anisotropic dry etching technique for graphene. The etching depends strongly on its crystal orientation, resulting in zigzag-edge formation. The etching rates can be precisely controlled to several nm/min by plasma intensity and temperature. The etching only starts at defect sites and the quality of graphene can be preserved. This simple technique is compatible with existing semiconductor processing technology, thus it is useful for large-scale graphene tailoring and defect detection. We have fabricated graphene nanoribbons (GNRs) along designed crystallographic directions, which have shown high nobilities and smooth zigzag edges with localized metallic edge state. Besides, we have directly identified the structural defects in graphitic materials (for example HOPG, Kish graphite, CVD graphene, SiC epitaxial graphene, etc) through defect etching magnifying technique. Rich information on their structural disorders including the defects types, defect densities, lattice orientations, stacking disorders, grain sizes and grain boundaries were extracted. [Preview Abstract] |
|
V1.00022: Controlling magnetism in graphene by molecular doping Rahul Raveendran Nair, I-Ling Tsai, Margherita Sepioni, Andre K. Geim, Irina V. Grigorieva Graphene, the first truly two dimensional crystal, continues to attract intense interest due to its extraordinary properties. The possibility to induce magnetism in graphene, despite the absence of d- or f-electrons, has been a subject of great excitement but is still poorly understood experimentally and the possibility of magnetic coupling remains controversial. Our recent experiments provided the first definitive proof that point defects in graphene -- adatoms and vacancies -- carry magnetic moments, giving rise to paramagnetism that dominates graphene's magnetic response at low temperatures [1]. In this contribution we show that one can control magnetism in graphene by using chemical doping. In order to vary the carrier concentration $n$, we used molecular (hole) doping of graphene laminates by NO$_{2}$ or nitric acid and were able to vary $n$ between $\sim$5x10$^{11}$ to $\sim$10$^{13}$ cm$^{-2}$ as estimated by Raman spectroscopy and Hall effect measurement. This had a pronounced effect on the magnetisation of graphene laminates, which was measured using SQUID magnetometry. Our results show that both para- and diamagnetic response of graphene can be controlled precisely and reversibly by the doping level, which opens up a new avenue of tuneable magnetism in graphene. \\[4pt] [1] R.R. Nair \textit{et al}., Nature Physics \textbf{8}, 199 (2012). [Preview Abstract] |
|
V1.00023: Origin Of Magnetism in Graphene Nanostructures Wen Ying Ruan, Yiyang Sun, Sheng-Bai Zhang, Mei-Yin Chou The magnetic orderings of traditional magnetic materials originate from their partially filled $d$- or $f$-electron bands. Surprisingly, theoretical and experimental studies show that graphene nanostructures which contain only $s$ and $p$ electrons can also exhibit magnetic ground states. On the basis of the bonding properties of $pi$-electrons, we propose a theoretical model to explain the origin of magnetism in graphene nanostructures. Our theory is justified via examples ranging from nanoflakes to nanoribbons. Our theory also provides a simple physical insight into Lieb's theorem about the ground state magnetic momentum of a bipartite system. [Preview Abstract] |
|
V1.00024: Surface Vibrational Modes in Multilayer Graphene Gregory Coard, Jia-An Yan The surface vibrational modes in multilayer graphene are studied based on both density-functional theory and the force constant model. It is found that these modes are mainly localized on the surface layers. The relationship between these modes and the stacking order as well as the layer number will be discussed. [Preview Abstract] |
|
V1.00025: Electron diffraction studies on CVD grown bi-layered graphene Kiran Lingam, Mehmet Karakaya, Ramakrishna Podila, Haijun Quin, Apparao M. Rao Graphene has generated enormous interest in the scientific community due to its peculiar properties like electron mobility, thermal conductivity etc. Several recent reports on exfoliated graphene emphasized the role of layer stacking on the electronic and optical properties of graphene in case of bi-layered and few layered graphene and several synthesis techniques like chemical vapor deposition (CVD) on Copper foils are employed to prepare graphene for applications at a large scale. However, a correlated study pertinent to the stacking order in CVD grown graphene is still unclear. In this work, using a combination of Raman spectroscopy and selected area electron diffraction analysis we analyzed the preferred misorientation angles in a CVD grown bi-layered graphene and also the role of Cu crystal facets on the graphene stacking order will be presented. [Preview Abstract] |
|
V1.00026: Multifunctional Crumpling and Unfolding of Large-Area Graphene Xuanhe Zhao Crumpled graphene films of atomic thickness are used in diverse applications including electronics, energy storage, composites, and biomedicine. While it is known that the degree of crumpling strongly affects the properties of graphene and the performance of graphene-based devices and materials, in existing technology it is not possible to fold and unfold crumpled graphene films in a controlled manner. Here we present a new approach, investigated by joint experiment, atomistic simulation and theory, to control reversible crumpling and unfolding of large-area graphene, achieved by harnessing mechanical instabilities of graphene adhered on highly pre-strained polymer substrate. By relaxing the pre-strain in the substrate in a particular order, we crumple graphene films into tailored self-organized hierarchical structures that mimic super-hydrophobic leaves. The degree of crumpling in graphene is controlled by stretching/relaxing the substrate. The reversible crumpling and unfolding of graphene films enables us to fabricate large-area conductive coatings and electrodes capable of giant stretchability, high transparency, super-hydrophobicity, and tunable wettability. We further demonstrate the use of novel graphene-polymer laminates as artificial muscles. [Preview Abstract] |
|
V1.00027: Fabricating graphene devices from graphite intercalation compounds Ryuta Yagi, Midori Shimomura, Fumiya Tahara, Seiya Fukada We report a method of making few-layer graphene flakes by mechanically exfoliating SbCl$_5$-graphite intercalation compounds (GICS). The number of exfoliated graphene flakes had a peculiar distribution relevant to the stage structure of GICs. The carrier doping of the few-layer graphene flakes was about two orders of magnitude smaller than that expected from the stoichiometry of the GICs. The measured electric mobility was comparable to that made from pristine graphite. The EPMA measurement showed that inhomogeneous distribution of dopant near the surface of GIC was responsible for obtaining the virtually undoped graphene. Deintercalation of dopant would expand interlayer distance of each graphene layer, and thereby layer-number of exfoliated graphene depended stage number of GIC. [Preview Abstract] |
|
V1.00028: Valley beam splitter device based on giant lateral shift in strained Graphene Neetu Agrawal, Manish Sharma, Sankalpa Ghosh The prospect of strain engineering to control electronic properties has opened up new directions for graphene research. Strain essentially can be considered as a perturbation to the in-plane hopping amplitude, which induces a gauge potential in the effective Hamiltonian which has opposite signs in the two valleys. Thus, strain can induce a valley-dependent magnetic field. We investigate the combined effect of commensurate scalar and vector potentials on a pair of region of uniform uniaxial strain. The strained region induces opposite gauge potentials leading to a valley dependence of the transverse velocity of incident valley unpolarised beam, while quasibound states arising due to well formation between the double unit structure give rise to giant lateral shifts. Thus lateral displacement of transmitted beams from $K$ and $K^{'}$ valleys together with their difference can be enhanced to a very large extent thereby enabling a highly efficient valley beam splitting. The wide tunability of proposed device is facilitated due to the presence of external vector potential. This vector potential acts in a similar way at the two valleys, thereby providing a handle to manipulate the net effect of strain. [Preview Abstract] |
|
V1.00029: Light-matter interaction in a microcavity-controlled graphene transistor Ralph Krupke, Michael Engel, Mathias Steiner, Antonio Lombardo, Andrea Ferrari, Hilbert v. Loehneysen, Phaedon Avouris Graphene has extraordinary electronic and optical properties and holds great promise for applications in photonics and optoelectronics. Demonstrations including high-speed photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have now been reported. more advanced device concepts would involve photonic elements such as cavities to control light-matter interaction in graphene. Here we report the first monolithic integration of a graphene transistor and a planar, optical microcavity. We find that the microcavity-induced optical confinement controls the efficiency and spectral selection of photocurrent generation in the integrated graphene device. A twenty-fold enhancement of photocurrent is demonstrated. The optical cavity also determines the spectral properties of the electrically excited thermal radiation of graphene. most interestingly, we find that the cavity confinement modifies the electrical transport characteristics of the integrated graphene transistor. our experimental approach opens up a route towards cavity-quantum electrodynamics on the nanometre scale with graphene as a current-carrying intra-cavity medium of atomic thickness. [Preview Abstract] |
|
V1.00030: Dynamic Charge Transfer at the C$_{60}$/Graphene Interface Rui Wang, Xiaowei Wang, Shengnan Wang, Zhihai Cheng, Xiaohui Qiu The charge transfer dynamics between C$_{60}$ molecules and graphene was studied using scanning probe microscopy, micro-Raman spectroscopy and transport measurement. Electrons inject from graphene to C$_{60}$ molecules due to the hybridization of energy band was observed. The charged C$_{60}$ molecules act as local electrical gates, which are thermally switching and induce the current or resistance fluctuations (such as 1/f noise) in graphene active channel. The thermally activated carrier trapping/detrapping process was found to be a dominant source for the 1/f noise at room temperature. As temperature decreased, Coulomb scattering from charged C$_{60}$ molecules became a primary influence on the current flow in graphene transistors. [Preview Abstract] |
|
V1.00031: Magnetotransport through a graphene quantum ring Damien Cabosart, Sebastien Faniel, Frederico Martins, Thanh Nhan Bui, Cristiane Nascimento Santos, Vincent Bayot, Benoit Hackens, Jessica Campos Delgado We report on four-leads electrical resistance measurements in graphene quantum rings (QRs) at low temperature. Our samples were fabricated by exfoliating natural graphite on SiO$_2$ to form graphene monolayers. The graphene sheets have been located and characterized by optical contrast and Raman spectroscopy. The QRs were patterned by e-beam lithography and oxygen plasma etching. The graphene devices were electrically contacted thanks to Ti/Au (5nm/60nm) pads, obtained after lithography and lift-off. The measurements were performed down to 20 mK in the coherent and diffusive regime of electron transport. A back gate allowed us to manipulate the carrier concentration in the graphene layer. We measured Universal Conductance Fluctuations (UCFs) by tuning the back gate voltage as well as the magnetic field applied perpendicular to the ring. Analyzing the UCFs, we obtain invaluable information on the dynamics of phase coherent transport inside our QRs. [Preview Abstract] |
|
V1.00032: Noise properties of graphene films Nan Sun, Xinyu Liu, Gerald Arnold, Steven Ruggiero We present results for the noise characteristics of graphene flakes on SiO$_{2}$ as a function of gate bias. Our results are in accord with a new tunnel/trap model~based on the interaction of graphene carriers with the underlying substrate, which incorporates trap position, energy, and barrier height for tunneling into a given trap, along with the band-structure of the graphene. We will also discuss recent work on the properties of MBE-grown GaAs on graphene, in the context of noise in spin transport. [Preview Abstract] |
|
V1.00033: Oxide-on-graphene field effect biosensors Bei Wang, Kristi Liddell, Junjie Wang, Brandon Koger, Christine Keating, J. Zhu Nanoelectronics-based detection schemes offer fast and label-free alternatives to bioanalysis. Here we report on the design, fabrication, and operation of ion-sensitive field-effect biosensors using large-area graphene sheets synthesized by chemical vapor deposition. The graphene transducer channel has a high carrier mobility of approximately 5000cm$^{2}$/Vs. Our oxide-on-graphene design uses thin HfO$_{2}$ and SiO$_{2}$ films to passivate the graphene channel and electrodes from electrolyte and uses the top SiO$_{2}$ surface for sensing and linker chemistry. The pH sensitivity of the bare SiO$_{2}$ is measured to be 46mV/pH, in good agreement with literature results. We demonstrate the silanization of the SiO$_{2}$ surface with aminopropyl-trimethoxysilane (APTMS). The pH sensitivity of the APTMS-functionalized SiO$_{2}$ is measured to be 43mV/pH. By applying the solution gate voltage in pulse, we eliminate hysteresis in the transfer curve of the graphene channel, which is a common challenge in achieving high-solution detection using nanostructure-based field effect sensors. The amine-functionalized SiO$_{2}$ surface can be further functionalized with bio-probes to perform the detection of specific binding events such as DNA hybridization. [Preview Abstract] |
|
V1.00034: Fabrication of Single-layer Graphene Nanomechanical Oscillators by Deep-UV Lithography on Poly(methyl methacrylate) (PMMA) Jen-Feng Hsu, Shonali Dhingra, Brian D'Urso Graphene is well-known for its conductivity and high mechanical strength. Its lightness and stiffness can be exploited for oscillation devices. It also makes promising candidates for quantum nano-mechanical device. And since it's a conductive material, the oscillator can be driven electrically. Here we present a simple and scalable graphene patterning technique for suspended nanomechanical oscillator (NMO) in various geometrical shapes, including doubly clamped beams, circular drums and rectangular drums, in sizes of $\approx$ 2 - 4 $\mu$m. The graphene in this work is synthesized by chemical-vapor deposition (CVD) on $\approx$ 2mm thick copper substrates which is later thinned down by single-point diamond turning for transfer. The patterning method employs deep-UV (240-310nm) lithography to expose the PMMA layer on top of the graphene layer. Oxygen plasma may be used to transfer patterns onto the graphene film. The PMMA layer further acts as clamping material for drum devices. This method avoids any metal or contamination and devices in different shapes have unique advantages such as torsional modes (beams) and higher quality factors (drums). [Preview Abstract] |
|
V1.00035: ABSTRACT WITHDRAWN |
|
V1.00036: Ethane adsorption on as-produced nanohorns Brice Russell, Aldo Migone, Masako Yudasaka, Sumio Iijima We report on an ongoing adsorption isotherm study of ethane on as-produced (closed) single-walled carbon nanohorns. We have completed measurements at two temperatures: 130 K and 140 K. Steps in the logarithmic plots of the isotherms indicate the presence of two different groups of binding energy sites, which we interpret as corresponding to different sized pore regions in the nanohorn aggregates. We will present results of the application of the point B method for the determination of the effective monolayer capacity and for the effective specific surface area values at each temperature. The isosteric heat as a function of sorbent loading will be obtained from the isotherm data. The results obtained for ethane on the closed nanohorn aggregates will be compared to those previously obtained for ethane adsorbed on bundles of closed single-walled carbon nanotubes. [Preview Abstract] |
|
V1.00037: Recording Single Molecule Dynamics and Function using Carbon Nanotube Circuits Yongki Choi, Patrick Sims, Issa Moody, Tivoli Olsen, Brad L. Corso, O. Tolga Gul, Gregory A. Weiss, Philip G. Collins Nanoscale electronic devices like field-effect transistors (FETs) have long promised to provide sensitive, label-free detection of biomolecules. In particular, single-walled carbon nanotubes (SWNTs) have the requisite sensitivity to detect single molecule events, and have sufficient bandwidth to directly monitor single molecule dynamics in real time. Recent measurements have demonstrated this premise by monitoring the dynamic, single-molecule processivity of three different enzymes: lysozyme, protein Kinase A, and the Klenow fragment of polymerase I. Initial successes in each case indicate the generality and attractiveness of SWNT FETs as a new tool to complement other single molecule techniques. Furthermore, our focused research on transduction mechanisms provides the design rules necessary to further generalize this SWNT FET technique. This presentation will summarize these rules, and demonstrate how the purposeful incorporation of just one amino acid is sufficient to fabricate effective, single molecule nanocircuits from a wide range of enzymes or proteins. [Preview Abstract] |
|
V1.00038: Hydrogen Adsorption in Carbon nanoparticles A.L. Cabrera, S. Rojas, D.E. Dias-Droguett, H. Bhuyan, N. Aomoa, M. Kakati We have studied hydrogen adsorption in carbon nanoparticles using a quartz crystal microbalance. The carbon nanoparticles were synthesized from a thermal plasma jet at different pressure (\textit{15 -- 263 torr}) of the reactants and different current (\textit{50 -- 250 A}) to generate the plasma. The as-prepared carbon nanoparticles were directly deposited on top of the gold electrode of a quartz crystal and we monitored in-situ the changes in resonance frequency while the chamber was pressurized at different hydrogen pressures. These changes enabled determination of absorbed hydrogen mass in order to get H/C mass ratio curves as a function of H$_{\mathrm{2}}$ pressure. Adsorption curves obtained in some carbon nanoparticles indicated the formation of hydrogen monolayer inside the pores of the carbon nanoparticles. Using the value of the jump due to the formation of a H$_{\mathrm{2\thinspace }}$monolayer, a surface area was estimated between 40-60 m$^{\mathrm{2}}$/g for hydrogen adsorption. In other carbon samples, hydrogen uptake curves indicated that H$_{\mathrm{2}}$ was filling the sample's pores when pore volume was large. These observations will be discussed in detail for several carbon nanoparticles samples. [Preview Abstract] |
|
V1.00039: Electronic structure of carbon-boron nitride nanotubes Ra\'ul Sangin\'es-Mendoza, Edgar Martinez Structures of carbon and boron nitride nanotubes (CNTs, BNNTs) are quite similar, conversely, electronic properties are radically different from each other. Carbon nanotubes, whose electronic properties can be either metallic or semiconducting depending on their chiral structure, boron nitride nanotubes are always semiconductors with bandgaps over 4 eV. We have looked to hybrid systems, to predict a new kind of nanostructures with novel electronic properties. In this way, we explore the electronic properties of C-BN nanotubes. In particular, we studied the electronic structure of armchair C-BN nanotubes. The calculations were performed using the pseudopotential LCAO method with a Generalized Gradient Approximation for the exchange-correlation energy functional. The band structure of most of these systems have semiconductor character with an indirect gap smaller than its analogous BNNTs. In addition, the most prominent feature of these systems is the existence of flat bands both at the valence band top and at the conduction band minimum. Such flat bands results in sharp and narrow peaks on the total density of states. The behavior of these flat bands mainly indicates that electrons are largely localized. Thus, a detailed analysis on the electronic band structure shows that hybridization between those orbitals on the interfaces is responsible to exhibit localization effects on the hybrid systems.This research was supported by Conacyt under Grant No. 133022. [Preview Abstract] |
|
V1.00040: Efficiency enhancement in encapsulated thermoacoustic projector based on carbon nanotubes Ali Aliev, Yuri Gartstein, Ray Baughman Carbon nanotubes (CNT) can generate sound by means of thermoacoustics over a wide frequency range (1-10$^{5}$ Hz). However, the low sound generation efficiency of open CNT films at low frequencies ($\eta \propto f^{2})$, where the demands for large size and flexible sound projectors is high, is frustrating. The nanoscale thickness of CNT film, high sensitivity to the environment and high surface temperatures required for TA sound generation are another drawbacks suggesting an efficient protection of free-standing CNTs, demonstrated in this work by means of encapsulation in inert gases. We analyze the effect of different thermodynamic regimes on fundamental efficiency of thermoacoustics sound generation for closed system using first principle calculation and experimental investigation of encapsulated sound projector's performance. The observed sound pressure level for argon gas encapsulated transducers $Q$ times higher than for open system, where $Q$ is a resonant quality factor of thin vibrating plates. Moreover, the sound generation efficiency for encapsulated system is increased toward low frequencies ($\eta \propto $1/$f^{2})$. The acoustical and geometrical parameters of resonant system for further increase of efficiency and transduction performance are discussed. [Preview Abstract] |
|
V1.00041: Dopants as Morphology Promoters: a Fundamental Study of the Role of Boron and Sulfur in the Formation of MWNT Junctions Lakshmy Pulickal Rajukumar, Ana Laura Elias, Amber D. McCreary, Arava Leela Mohana Reddy, Kaushik Kalaga, Nestor Perea-Lopez, Martha E. Audiffred, David Swanson, Humberto R. Gutierrez, Robert Vajtai, Pulickel M. Ajayan, Humberto Terrones, Mauricio Terrones We have synthesized CNT-based hierarchical structures via an aerosol assisted CVD process. Our experiments consist of pyrolyzing a solution containing C and Fe sources together with small amounts of B and S sources (800-900C, Ar atmosphere). The resulting structures consist of micron-size fibers decorated with short multi-walled carbon nanotubes that resemble ``nanotentacles.'' The materials have been characterized by SEM, HRTEM, EELS, TGA, XRD, XPS and Raman spectroscopy. Finally, these materials have been tested for its possible application in batteries and supercapacitors. [Preview Abstract] |
|
V1.00042: Large-area tungsten diselenide atomic layers on an insulator substrate grown by vapor phase chemical deposition Kwonjae Yoo, Il-Suk Kang, Yehoon Park, Chi Won Ahn, Jongwoo Shin, Dae Yool Jung, Byung Jin Cho, Sung-Yool Choi, Hongkyw Choi Group IV transition metal dichalcogenides such as WS2 and WSe2 are one of attracting material classes which have a physical two dimension of one atomic layer and atomically thin layers like graphene. These materials have interesting features such as an indirect bulk gap makes a transition to a direct band gap in monolayer. Recent research results of FETs showed that a high effective hole mobility of 250 cm$^2$ /V s with subthreshold swing of 60 mV/dec from an exfoliated monolayer. Indeed it is natural to think that artificial large area synthesis is needed for practical applications. Here we report the large-area tungsten diselenide layers on SiO2 substrate using vapor phase deposition method. Selenium source was evaporated from certain distances to a tungsten thin film on SiO2/Si wafer. Nitrogen gas was flowed during all processes as a carrier gas. Growth was performed at 700 $\sim$ 900 Celsius degree. The size of atomic tungsten diselenide layers simply depends on a wafer and quartz tube size. Good qualities of selected tungsten diselenide layers were investigated by AFM/EFM, SEM/TEM, and Raman spectroscopy. FET and PL data also will be presented. [Preview Abstract] |
|
V1.00043: Ferroelectric Tuning of Photocatalytic Water Splitting on Epitaxially-Strained TiO$_2$/SrTiO$_3$ Hetero-Structure Jun Hee Lee, Annabella Selloni Using first-principles density functional theory (DFT) calculations, we show that the electric-dipole moment and epitaxial strain in heterostructures of TiO$_2$ with polar oxides such as SrTiO$_3$ can be used as control parameters to tune the activity of TiO$_2$ toward water splitting. Specifically, we find that the ferroelectric dipole of strained SrTiO$_3$ rigidly shifts the band-edge-energy positions of epitaxial TiO$_2$ films and affects the adsorption of relevant species (OH, H) on the TiO$_2$ surface. By varying the magnitude of the electric dipole moment and epitaxial strain, this effect can facilitate the oxygen evolution reaction and hydrogen production on TiO$_2$. In particular, our results show that a positive electric dipole pointed toward TiO$_2$ and compressive epitaxial strain can strongly reduce the barrier for oxygen evolution and thus significantly enhance the photocatalytic efficiency of TiO$_2$. [Preview Abstract] |
|
V1.00044: Computational modeling of mechanical response of dual cross-linked polymer grafted nanoparticle networks Balaji Iyer V S, Victor Yashin, Isaac Salib, Tomasz Kowalewski, Krzystof Matyjaszewski, Anna Balazs We develop a hybrid computational model for the behavior of a network of cross-linked polymer-grafted nanoparticles (PGNs). The individual nanoparticles are composed of a rigid core and a corona of grafted polymers that encompass reactive end groups. With the overlap of the coronas on adjacent particles, the reactive end groups can form permanent or labile bonds, which lead to the formation of a ``dual cross-linked'' network. To capture these multi-scale interactions, our approach integrates the essential structural features of the polymer grafted nanoparticles, the interactions between the overlapping coronas, and the kinetics of bond formation and rupture between the reactive groups on the chain ends. We investigate the mechanical response of the dual-cross linked network to an applied tensile deformation. We find that the response depends on the bond energies of the labile bonds, the fraction of permanent bonds in the network, and thickness of the corona. This model provides a powerful tool for the computational design of dual cross-linked PGN's by predicting how the structural features of the system affect the mechanical performance. [Preview Abstract] |
|
V1.00045: Stable, Single-Layer MX$_{2}$ Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure Can Ataca, Hasan Sahin, Salim Ciraci Recent studies have revealed that single-layer transition-metal oxides and dichalcogenides (MX$_{2})$ might offer properties superior to those of graphene. So far, only very few MX$_{2}$ compounds have been synthesized as suspended single layers, and some of them have been exfoliated as thin sheets. Using first-principles structure optimization and phonon calculations based on density functional theory, we predict that, out of 88 different combinations of MX$_{2}$~compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures. Our analysis of stability was extended to include in-plane stiffness, as well as ab initio, finite-temperature molecular dynamics calculations. Some of these single-layer structures are direct- or indirect-band-gap semiconductors, only one compound is half-metal, and the rest are either ferromagnetic or nonmagnetic metals. Because of their surface polarity, band gap, high in-plane stiffness, and suitability for functionalization by adatoms or vacancies, these single-layer structures can be utilized in a wide range of technological applications, especially as nanoscale coatings for surfaces contributing crucial functionalities. In particular, the manifold WX$_{2}$ heralds exceptional properties promising future nanoscale applications. [Preview Abstract] |
|
V1.00046: Crystalline $\alpha $-samarium sesquisulfide nanowires: structure and electronic properties of an unusual intrinsically degenerate semiconductor Chris Marin, Joseph Brewer, Chin Li Cheung, Lu Wang, Wai-Ning Mei We report that $\alpha $-phase samarium sesquisulfide ($\alpha $-Sm2S3) intrinsically takes on an electronic structure similar to that of a heavily degenerate p-type semiconductor by means of UV-Vis absorption spectroscopy and first-principles calculations. When prepared by chemical vapor deposition, these samples were found to have a tendency to crystallize as bundles of nanowires. Additional characterizations using high-resolution electron microscopy, along with selected area electron diffraction and X-ray diffraction, were applied to verify the matching of the modeled structure of $\alpha $-Sm2S3 to that of the experimentally measured material. We expect this compound to be intrinsically well suited for potential applications in the p-type elements of diode devices such as in photovoltaic devices and thermo-electric converters. [Preview Abstract] |
|
V1.00047: Structural and Oxygen Storage Properties of Hexagonal Manganites Castro Abughayada, Bogdan Dabrowski, Stan Kolesnik, Omar Chmaissem Complex oxides exhibiting superior reversible oxygen absorption/release capacities have been generating a great deal of interest due to their critical role in the development of energy related technologies, such as oxy-fuel and chemical looping combustion. Based on our previous studies of tolerance factor, we have successfully synthesized hexagonal (P6$_{3}$cm) RMnO$_{3+\delta}$ manganites (R$=$Dy, Ho, Y) for which we discovered a large reversible oxygen storage/release capacities (within the range of oxygen content 3.0 - 3.4) at unusually low temperatures near 300 $^{\circ}$C which make them excellent candidates for air separation and production of high purity oxygen. Resistivity, structural, magnetic, and thermal expansion properties are correlated with the oxygen content 3$+\delta $ for these compounds. Work supported by NIU Great Journey Assistantship. [Preview Abstract] |
|
V1.00048: Temperature Dependence of the Raman Spectra of Mechanically Exfoliated Monolayer MoS$_{2}$ A. Glen Birdwell, Frank J. Crowne, Terrance P. O'Regan, Pankaj B. Shah, Madan Dubey, Lili Yu, Han Wang, Tomas Palacios, Rusen Yan, Huili Grace Xing We investigated the temperature dependence of the E$^{1}_{\mathrm{2g}}$ and A$_{\mathrm{1g}}$ peaks in the Raman spectra of monolayer MoS$_{2}$ prepared by mechanical exfoliation (ME) onto Si/SiO$_{2}$ substrates. Micro-Raman spectroscopy was carried out using the 532 nm laser excitation over the temperature range from 30 to 175 $^{\circ}$C. Extracted values of the temperature coefficient for these modes will be presented in conjunction with the effect of excessive laser power on these measurements. These results suggest power densities as low as $\approx $ 275 $\mu $W/$\mu $m$^{2}$ can still cause local heating in ME-MoS$_{2}$ monolayer samples. [Preview Abstract] |
|
V1.00049: Ultrafast photocurrents and THz generation in single InAs-nanowires Alexander Holleitner, Nadine Erhard, Gerhard Abstreiter, Gregor Koblmuller Conventional scanning photocurrent microscopy experiments on semiconductor nanowires are typically limited to timescales exceeding 10 ps. Yet, it is known from optical experiments that carrier relaxation and transport processes can occur on much faster timescales in such wires. We therefore apply a recently developed pump-probe photocurrent spectroscopy based on coplanar striplines [1] to investigate the photocurrent dynamics of single GaAs- and InAs-nanowires with a picosecond time-resolution [2]. The ultrafast photocurrent response of the nanowires is sampled in the time-domain with the help of Auston switches. We discuss data on single InAs-nanowires which are interpreted in terms of a photo-thermoelectric current and the transport of photogenerated holes to the electrodes as the dominating ultrafast photocurrent contributions. Moreover, we show that THz radiation is generated in the optically excited InAs-nanowires, which we interpret in terms of a dominating photo-Dember effect [3]. The results are relevant for nanowire-based optoelectronic and photovoltaic applications as well as for the design of nanowire-based THz sources. [1] L. Prechtel, et al. Nature Communications 3, 646 (2012). [2] L. Prechtel, et al. Nano Letters . 12, 2337 (2012). [3] N. Erhard, et al. (2013). [Preview Abstract] |
|
V1.00050: Ab-initio study of field emission characteristics of single-walled ZnO nanotubes Wei-Chih Chen, Feng-Chuang Chuang, Zhi-Quan Huang, Wan-Sheng Su We employed first-principles calculations to investigate the field emission characterictics of infinite-length single-walled ZnO nanotubes (SWZONTs) in the either armchair or zigzag conformations. Both armchair and zigzag SWZONTs are found to be direct-bandgap semiconductors. Moreover, our calculations demonstrated that work functions of armchair and zigzag tubes decrease from about 5.70 to 5.25 eV with an increasing tube diameter, and it eventually approaches to the work function value of a ZnO sheet with a diameter close to an infinite limit. Finally, the direct computations on file emission factors of both nanotubes will be presented. Our findings provide an insight into the ZONT field-emission properties as well as contribute to developing procedures to produce an efficient ZONT field emitter. [Preview Abstract] |
|
V1.00051: Co-adsorptions of Hydrogen and Oxygen Molecules in Armchair Silicon Nanotubes Haoliang Chen, Asok Ray A systematic study of the interactions of hydrogen and oxygen molecules with armchair silicon nanotubes using the finite cluster approximation and the Gaussian09 suite of software is presented. Hydrogen and oxygen molecules have been adsorbed from both inside and outside of the nanotube. The admolecules were placed initially perpendicular to the tube axis in four different adsorption sites- normal bridge, zigzag bridge, hollow and on-top sites. After adsorption, the two hydrogen molecules maintained their original diatomic linear structure and the most preferred site is the on-top site, with the highest adsorption energy being 3.714eV. For adsorption of two oxygen molecules, complete dissociation, partial dissociation and non-dissociation were noted, with the highest adsorption energy being 7.659eV. We propose several precursor (or metastable) states, such as the Si-O-O-Si peroxide structure, which has a lower ground state energy than dissociative adsorption. For the co-adsorption of one hydrogen molecule with one oxygen molecule, the oxygen molecule dissociated into oxygen atoms and hydrogen molecule prefers to stay in on-top site, the highest adsorption energy being 5.563eV. [Preview Abstract] |
|
V1.00052: Exploring epitaxial relationships between InAs nanowires and shaped Au nanoparticles Debosruti Dutta, R. Mohan Sankaran, Xuan Gao, Venkat R. Bhethanabotla The high electron mobility and strong spin-orbit interactions make InAs nanowires (NWs) an excellent material for the micro-electronics industry. However, our inability to precisely control their structural properties like defects, crystalline orientation, etc pose a significant obstacle to their widespread usage. Recent evidence in the literature suggests an epitaxial relationship exists between the structural properties of a NW and, the size and shape of the metal seed nanoparticle (NP) from which it is grown. In this work, we have explored the epitaxial relationship between H-terminated [111] zinc blende (ZB) and [0001] wurtzite (WZ) InAs NW fragments with the (111) {\&} (100) facets of Au NP using density functional theory calculations. The binding energies suggest greater stability of ZB [111] over WZ [0001] fragments on Au surface facets with both fragments being more stabilized by Au (111) than Au (100) surface. This suggests that shaped Au NPs with a higher number of Au (111) facets should produce higher yields of InAs NWs, with (111) growth directions. A chemical potential based Arrhenius model that takes into account these binding strengths, is used to compare the relative thermodynamic stability of these NW-NP interactions. [Preview Abstract] |
|
V1.00053: ABSTRACT WITHDRAWN |
|
V1.00054: Chirality Distribution Measurements of the NIST Single-Wall Carbon Nanotube Reference Material Using Resonance Raman Spectroscopy Kevin Mead, Jeff Simpson, Logan Scheel, Jeff Fagan, Angela Hightwalker The ability to rapidly and easily determine the chiral vector distribution within a nanotube population remains a key measurement need for carbon nanotube processing and applications. We report Resonance Raman Spectroscopy (RRS) measurements of a SWCNT reference material from NIST. The SWCNT samples were synthesized using the CoMoCat method, dispersed in aqueous solutions by wrapping in deoxycholate surfactant, and separated by length using ultracentrifugation. We measure Raman spectra over a wide range of excitation wavelengths from 457 nm to 850 nm using a series of discrete and continuously tunable laser sources coupled to a triple-grating spectrometer with a liquid-nitrogen-cooled detector. The spectra reveal Raman-active vibrational modes including the low-frequency radial breathing mode and higher-order modes. Chirality distributions are determined from the Raman spectra, specifically the RBM frequency and energy excitation profiles, together with input from theoretical models. RRS is sensitive to both major and minor chiral species in the sample. We will compare the resulting chirality distribution obtained from RRS with those obtained from other orthogonal measurement techniques. [Preview Abstract] |
|
V1.00055: Kondo effect in a dissipative environment Chung-Ting Ke, Henok Mebrahtu, Yuriy Bomze, Alex Smirnov, Gleb Finkelstein In this work, we study the competition between two many body-effects: Kondo effect and tunneling with dissipation. We work with nanotube quantum dots contacted by resistive leads, resulting in controlled dissipative environment for the tunneling electrons. Previously, we have demonstrated the existence of the quantum phase transition in a resonant level coupled to the dissipative environment in the spinless case. Here, we demonstrate that the Kondo effect can survive under weak enough dissipation strength. [Preview Abstract] |
|
V1.00056: Plasma excitations and self energy for gapped graphene in strong magnetic fields Andrii Iurov, Godfrey Gumbs The collective plasma excitations of gapped graphene such as may be induced by optically dressed Dirac electrons or by an underlying substrate have been calculated in the presence of a uniform perpendicular magnetic field. The polarization function was obtained using the random phase approximation (RPA). By varying the intensity and frequency of the polarized light, we may tune the energy gap $E_g$ between the conduction and valence bands. The value of $E_g$ may reach values by far exceeding that caused by spin-orbit coupling or that caused by a substrate. We report the magnetoplasmon dispersion relations for various energy gaps and for Coulomb coupled double layers with various separations between the graphene layers. [Preview Abstract] |
|
V1.00057: Edge-Saturation Effect on Finite Size 0-D Carbon Nano-Ribbons --- a Density Functional Theory Study Li Chen, Louis Cirello Using computational simulation and Density Functional Theory, we have studied the absorption of various foreign molecular/atomic groups saturated at the edge of semi-conducting, finite-size armchair carbon nano-ribbons (ACNR). The effect of this edge-saturation was studied in terms of its impact on HOMO-LUMO gap, electronic structure and spin distribution. A comparison was made between the non-saturated pristine ACNRs and saturated ones, as well as, between different saturation species, different doping sites, different doping concentration and ACNR length. Our results suggest that the type of elements play a more important role than the concentration and/or doping sites in terms of the change in HOMO-LUMO gap, which leads to the possibilities of using CNBs as nano-scale chemical sensors. The doping of some elements also introduces a spin distribution different from the pristine CNBs. [Preview Abstract] |
|
V1.00058: Theoretical study of static magnetic properties for the chiral and reconstructed graphene nanoribbons Suk-Young Park, Jun-Won Rhim, Kyungsun Moon Recent theoretical study of the chiral graphene nanoribbons(CGNR) has demonstrated the magnetic ordering of the edge states below a certain chiral angle$^{\mathrm{1}}$. Based on the Hubbard model for the CGNR, we study the static properties of the magnetic edge states such as the intra-edge and inter-edge spin stiffness, which are the two crucial parameters to control the thermodynamics of the effective magnetic hamiltonian. For the systematic study of the anti-ferromagnetic inter-edge spin correlations, we calculate the inter-edge spin stiffness as a function of ribbon width and transverse electric field. We also attempt to calculate the electronic and magnetic properties for the other edge geometries such as a reconstructed edge geometry, which has been experimentally confirmed as an edge shape other than zigzag or armchair nanoribbon$^{\mathrm{2}}$ 1. Oleg V. Yazyev, Rodrigo B. Capaz, and Steven G. Louie, Phys. Rev. B 84, 115406 (2011). 2. Pekka Koskinen, Sami Malola, and Hannu Hakkinen, Phys. Rev. B 80, 073401 (2009). [Preview Abstract] |
|
V1.00059: Ab initio study of boron nitride lines on graphene Berenice Mata-Carrizal, Ra\'ul Sangin\'es-Mendoza, Edgar Martinez Graphene has unusual electronic properties which make it a promising material for electronic devices. Neverthless, the absence of a band gap sets limitations on its practical applications. Thus, it is crucial to find methods to create and tune the band gap of systems based on graphene. In this way, we explore the modulation of the electronic properties of graphene through doping with boron nitride lines. In particular, we studied the electronic structure of graphene sheets doped with boron nitride lines armchair and zigzag type. The calculations were performed using the pseudopotential LCAO method with a Generalized Gradient Approximation (GGA) for the exchange-correlation energy functional. We found that both doping lines type induce a bandgap and that the energy gap increases as the length of doping lines increases. Accordingly to our DFT calculations, we found that the energy gap on graphene doped with armchair and zigzag lines is due to a two different mechanisms to drain charge from pi- to sigma- orbitals. Thus, we found that doping graphene with boron nitride lines is a useful way to induce and modulate the bandgap on graphene. This research was supported by Consejo Nacional de Ciencia y Tecnolog\'ia (Conacyt) under Grant No. 133022. [Preview Abstract] |
|
V1.00060: Phonon bottleneck in graphene-based Josephson junctions at millikelvin temperatures. Ivan Borzenets, Ulas Coskun, Henok Mebrahtu, Yuriy Bomze, Alex Smirnov, Gleb Finkelstein We examine the nature of the transitions between the normal and the superconducting branches of superconductor-graphene-superconductor Josephson junctions. We attribute the hysteresis between the switching (superconducting to normal) and retrapping (normal to superconducting) transitions to electron overheating. In particular, we demonstrate that the retrapping current corresponds to the critical current at a higher temperature, where the heating is caused by the retrapping current itself. The superconducting gap in the leads suppresses the hot electron outflow, allowing us to further study electron thermalization by phonons at low temperatures ($T <1$K). The relationship between the applied power and the electron temperature was found to be $P\propto T^3$, which we argue is consistent with cooling due to electron-phonon interactions. [Preview Abstract] |
|
V1.00061: Magneto-electronic properties of multilayer graphenes Jei Wang, Jhao-Ying Wu, Chen-Peng Chang, Ming-Fa Lin We develop the generalized Peierls tight-binding model to study the low-energy electronic properties of multilayer graphenes (MLGs) in a uniform perpendicular magnetic field. The Landau levels (LLs) in MLG can be categorized into some groups according to their wavefunction distributions among different sublattices. Their dispersions strongly depend on the field strength, layer number and stacking configuration. The level degeneracies in even number of layers are the same with those in monolayer graphene, i.e., four-fold degeneracy. However, in odd number ones, most LLs are doubly degenerate because the spatial inversion symmetry is broken. There exist LL crossings or anti-crossings during the variation of magnetic field, a feature that may reflect in transport experiments. The carrier density distribution in zero fields is also included, which provides an alternative way to understand the grouped LLs. [Preview Abstract] |
|
V1.00062: Pinning of the electronic bands at the graphene and wet contact Ti junction Tobias Bothwell, Wei Ren, Salvador Barraza-Lopez Pinning of electronic bands has been observed at the junction of graphene and Ti contacts. Density functional theory is used to study this junction by analyzing the electronic bands of two systems. We study graphene atop a BN gate as well as Ti contacts atop the graphene and BN. Varying electric fields are applied in the vertical axis to study how the electronic bands shift. Contributions of each material to the bands are also analyzed. Calculations are performed using the Vienna Ab initio simulation package (VASP). [Preview Abstract] |
|
V1.00063: Bandgap opening in graphene templates on Ru(0001) from subsurface hydrogen effects studied by STM, LEED, and DFT Maxwell Grady, Bogdan Diaconescu, Darren Valovcin, Frank Hagelberg, Karsten Pohl Graphene has aroused tremendous interest due to its remarkable electronic and mechanical properties. Graphene's optical properties, conductance, and the fact that it can be transferred to many substrates make it an ideal candidate for use in nanoelectronic devices and organic photoelectric devices. The lack of a bandgap, however, causes a serious challenge for implementing graphene as a material for electrical switches and therefore creative ways of inducing this bandgap are needed. We will present a STM/LEED/DFT study of the single layer graphene on Ru(0001) system in the presence of hydrogen. Structural studies show arrays of moir\'e superlattices with sizes ranging from 0.9 to 3.0 nm in the presence of hydrogen on the compact surface of ruthenium. First principle calculations help explain the appearance of these arrays of graphene reconstructions driven by the H presence at the Ru(0001) interface, and furthermore, predict the appearance of a bandgap with values correlated with the moir\'e superstructure sizes in the presence of hydrogen. Control over moir\'e superstructure size can aid in future work using graphene as a nanotemplate for self assembled growth of nanoelectronic devices an organic photovoltaics. [Preview Abstract] |
|
V1.00064: Heat Confinement in Graphene Devices Using Superconducting Contacts Chris McKitterick, Heli Vora, Xu Du, Boris Karasik, Daniel Prober Many groups have proposed the use of graphene as a photon detector due to its very small heat capacity and thermal conductivity. We describe predictions of device performance taking into account the effect of device heating from incident photons using reported results [1]. To test the achievability of these predictions, we performed Johnson noise thermometry measurements of graphene samples fabricated at Stony Brook University. These measurements probe the electron-phonon behavior of graphene on SiO$_2$ at very low temperatures. Because the electron-phonon coupling is weak in graphene, this requires the use of superconducting contacts to confine the hot electrons and prevent their outdiffusion. To that end, NbN leads with a $T_{\mathrm{c}}\approx 11~$K are used to contact the graphene. The large energy gap present in these contacts prevents diffusive cooling for low electron temperatures. We present thermal conductivity measurements of these devices.\\[4pt] [1] C.B. McKitterick, B.S. Karasik, D.E. Prober, arXiv:1210.5495. [Preview Abstract] |
|
V1.00065: Effects of periodic scatter potential on the Landau quantization and ballistic transport of electrons in graphene Paula Fekete, Godfrey Gumbs, Danhong Huang The energy spectrum of graphene is calculated in the presence of a perpendicular magnetic field as well as a two-dimensional square array of scatterers. The potential modulation is simulated by a cosine function whose amplitude and period may be varied. This permits investigation of the effect that variation of the strength of and spacing between scattering centers has on the ballistic transport. We include both $K$ and $K'$ valleys as well as sublattices $A$ and $B$ to compute the four-component wave function. Additionally, based on our eigenenergy spectrum calculations, we determine the electron density of states for this system. [Preview Abstract] |
|
V1.00066: The effects of the layer number in optical excitations of AA-stacked graphenes Yuan-Cheng Huang, Chih-Wei Chiu, Ming-Fa Lin The band structures and the optical properties of AA-stacked multilayer graphenes are calculated by the tight-binding mode and the gradient approximation. For monolayer graphene, there are one pair of linear bands intersecting at Fermi level, and one pair of saddle points at $\pm \alpha_0$. As for the AA-stacked systems, $n_L$-layer graphenes own the $n_L$-pair energy bands. The energy dispersions of each pair are similar to those of the monolayer graphene, but shift upwards or downwards. The spacing of the conduction and valence bands in the same pair are slightly different among the different pairs. The threshold energy of the single-particle excitations ($\omega_s$) of the odd-layer graphene is much lower than those for the even-layer graphene, since there is one intersecting point much close to Fermi level only for the odd-layer graphene. When the layer number increases to 80, the effects of the odd-even layers vanish Furthermore, the features of the loss spectra of the multilayer graphene close to those of bulk graphite when $n_L$ increases more than 50 gradually. [Preview Abstract] |
|
V1.00067: Responsive Polymer Brushes on Graphene Oxide and Their Application as pH and Temperature Sensor K. Paek, H. Yang, J. Bang, B.J. Kim Light emitting responsive polymer brushes were synthesized and grafted on grapheme oxide (GO), and their pH and thermal responses were quantitatively investigated by photoluminescence (PL) quenching efficiency from fluorophores in polymer brushes to GO. First, GO was functionalized with pH responsive poly(acrylic acid) (PAA)-pyrene coated CdSe/ZnS quantum dots (QDs) by pi stacking interaction between pyrene and GO. The FRET from QDs to GO was controlled through manipulation of the conformational features of the PAA chains that respond to pH changes in solution. The PL intensity of QDs was gradually increased in the decreasing of pH value. As another example, temperature responsive GO was synthesized with poly(coumarine)-b-poly(N-isopropylacrylamide)-b-poly(azidostyrene) (PCou-b-PNIPAM-b-PSN3) by covalent bonding between PSN3 and GO. The PL of poly(coumarine) was completely quenched at the temperatures above LCST of PNIPAM due to the collapse of the PNIPAM spacer. Therefore, their temperature response can be demonstrated and monitored by the PL quenching efficiency, exhibiting reversible, well-defined on-and-off switching behavior. [Preview Abstract] |
|
V1.00068: Ultrafast collinear scattering and carrier multiplication in graphene Marco Polini Graphene is emerging as a viable alternative to conventional optoelectronic, plasmonic, and nanophotonic materials. The interaction of light with graphene creates a non-equilibrium carrier distribution, which first relaxes on an ultrafast timescale to a hot Fermi-Dirac distribution and then cools via phonon emission. While the slower relaxation mechanisms have been extensively investigated, the very initial stages of relaxation, ruled by fundamental electron-electron interactions, still pose a challenge. In this talk I will discuss recent results based on a pump-probe experiment featuring extreme temporal resolution (sub-10 fs) and broad spectral coverage. By comparing these results with a microscopic theory based on the Boltzmann equation I will shed light on the physical mechanisms that control the non-equilibrium dynamics of hot carriers in graphene. Reference: D. Brida, A. Tomadin, C. Manzoni, Y. J. Kim, A. Lombardo, S. Milana, R. R. Nair, K. S. Novoselov, A. C. Ferrari, G. Cerullo, and M. Polini, arXiv:1209.5729. [Preview Abstract] |
|
V1.00069: Optical absorption in trilayer graphene Xiao Li, Fan Zhang, Qian Niu We use a low energy effective model to analyze the optical responses of trilayer graphene samples. We first show that optical absorption of the ABA-stacked trilayer has strong dependence on both the Fermi energy and optical frequency, which is in sharp contrast to that of ABC-stacked trilayer graphene. Secondly, we are able to determine the possible existence of trigonal warping effects in the bandstructure of ABC-stacked trilayer graphene by a divergence in the absorption spectra at around 10 meV. In addition, we can partially distinguish the vairious broken symmetry states driven by electron-electron interactions in ABC-stacked trilayer graphene. In particular, the quantum anomalous Hall (QAH) state is sensitive to the polarization of the incident light, giving a way to detect its possible existence. [Preview Abstract] |
|
V1.00070: Asymmetric scattering of Dirac like electrons and holes Janice Wynn Guikema, Atikur Rahman, Nina Markovic We have studied magnetotransport and noise characteristics of dual-gated graphene p-n junction devices. The observed noise amplitude decreases rapidly with increasing temperature and its origin is related to the time-dependent quantum interference corrections. By comparing the results from the series and parallel p-n junctions, we show that the noise amplitude depends on the gate voltage and that the origin of the noise is not related to the fluctuation of resistance at the p-n junction interface. From the temperature and gate voltage dependence of resistance and noise characteristics, we show that the contribution from both short-range and long-range impurity determines the noise behavior and that the electrons and holes are asymmetrically scattered by the impurities. [Preview Abstract] |
|
V1.00071: Tunneling Effect across a Graphene Barrier Felix Marin We investigate a model of two macroscopic reservoirs which are separated by a graphene sheet. The sheets remain perpendicular to the reservoirs such that electrical conduction in the reservoirs is a three dimensional phenomena while graphene electrical conduction occurs perpendicular to the reservoirs. It means, as usual, that graphene electrical current is a bidimensional phenomena. We discuss the global electrical current as a function of the initial chemical potential of this system. The analysis include variations due to temperature and due to applied potentials to the reservoirs and to the graphene sheet. [Preview Abstract] |
|
V1.00072: Enhanced quantum coherence in graphene by Pd cluster absorption and its Golubev-Zaikin zero-temperature saturation Fengqi Song, Junhao Han, Shanyue Wang, Baigeng Wang, Guanghou Wang The absorption of functional impurities has been vastly proposed to mediate novel quantum coherent states, including quantum spin/anomalous Hall effects and Kondo effect etc, on graphene where the surface carriers dominate. However, such surface impurities will simultaneously introduce additional electronic scattering and suppress the electronic coherence of the Dirac fermions. This may eventually disable the expected quantum states. We report the increase of the dephasing lengths of the graphene sheet after the deposition of Pd nanoclusters, as demonstrated by the measurement of weak localizations. The dephasing lengths are found to reach some saturated values with the decreasing temperatures, essentially the zero-temperature decoherence. Detailed analysis is carried out on the temperature-dependent and saturated decoherence periods. The competition between the surface scattering and electrical field screening leads to the final improvement of quantum coherence. Our data agree well with the predication of Golubev and Zaikin, where such zero-temperature decoherence is induced by local fluctuations of the electrical fields near disorders. [Preview Abstract] |
|
V1.00073: Quantum Hall Effect near the charge neutrality point in graphene Jorge A. Leon, Guennadii M. Gusev, Flavio O. Plentz The Quantum Hall effect (QHE) of a two-dimensional (2D) electron gas in a strong magnetic field is one of the most fascinating quantum phenomena discovered in condensed matter physics. In this work we propose to study the transport properties of the single layer and bilayer of graphene at the charge neutrality point (CNP) and compare it with random magnetic model developed in theoretical papers in which we argue that at CNP graphene layer is still inhomogeneous, very likely due to random potential of impurities. The random potential fluctuations induce smooth fluctuations in the local filling factor around $\nu =$0. In this case the transport is determined by special class of trajectories, ``the snake states'', propagating along contour $\nu =$0. The situation is very similar to the transport of a two-dimensional particles moving in a spatially modulated random magnetic field with zero mean value. We especially emphasize that our results may be equally relevant to the composite fermions description of the half-filled Landau level. [Preview Abstract] |
|
V1.00074: Semiclassical Analysis of Landau levels Near the van Hove Singularity in Twisted Bilayer Graphen Chi-Ken Lu, Herbert Fertig We investigate the energy spectrum for electrons in twisted bilayer graphene in the presence of a weak magnetic field. Twisted bilayers host Dirac points from each layer that are near one another in the Brillouin zone, and are coupled through low energy saddle points. In the absence of a field these lead to a low energy van Hove singularity in the density of states. With the field, in a semiclassical picture, electrons orbit in momentum space on contours of constant band energy which may approach the saddle points. The orbits undergo an interesting change in topology as the energy passes from below to above the van Hove singularity energy, going from loops that separately surround each Dirac point to a single loop surrounding {\it neither}. This contrasts with the more standard situation in which the latter orbit surrounds {both} low energy orbit centers. The consequences for the Landau level spectrum of this unusual topological transition will be discussed. [Preview Abstract] |
|
V1.00075: SUPERLATTICES, NANOSTRUCTURES, AND OTHER ARTIFICIALLY STRUCTURED MATERIALS |
|
V1.00076: Quantum plasmon resonances and coupling of small nanoparticles Zapata-Herrera Mario, Florez Jefferson, Camacho Angela In this work, we propose to extend a theoretical quantum approach to describe the behavior of the optical response as a function of both size and shape of small metal nanoparticles. By using classical models as well as quantum approaches we also want to study the nanoparticle's permittivity in the whole range of nanometers in order to define the different regimes at the nanoscale. In particular, we are interested in examining size and shape effects on the enhancement field factor and the absorption spectra for comparing with possible experiments. We study the role played by Localized Surface Plasmon Resonance in the coupling of small metal nanoparticles pairs by varying the distance between them by using an analogy between molecular electronic states and plasmonic excitations as a function of particle size and shape. We pay special atention on tunnelling and multipolar effects in order to predict the regime of dimer formation. The main interest in understanding the plasmon resonances of small nanoparticles lies in the applications in biology, catalysis and quantum optics. [Preview Abstract] |
|
V1.00077: Optical and Magnetic Properties of WS$_2$: Single Layers, Clusters, and Nanoribbons Florentino Lopez-Urias, Humberto R. Gutierrez, Nestor Perea-Lopez, Ana Laura Elias, Ayse Berkdemir, Andres Castro-Beltran, Ruitao Ru, Humberto Terrones, Mauricio Terrones Transition metal chalcogenides are layered materials, similar to graphite. Inspired in recent experiments on the synthesis and photoluminesce enhancement of single-layer WS$_{2}$ sheets and triangular islands, in the present work, first-principles density functional theory calculations are carried out on different WS$_{2}$ nanostructures. In addition, we have studied WS$_{2}$ clusters with different 2-D morphologies, nanoribbons with zigzag and armchair edges, as well as single- and few-layered WS$_{2}$. The electronic density of states, scanning tunneling microscopy simulations, structural and magnetic ordering stability, and edge chirality are studied. Bethe-Salpeter equation for the electron-hole two particle Green function has been solved in order to calculate the in-plane polarized optical spectrum and exciton wave functions. In addition, the role of spin-orbit coupling on the electronic properties of single layer WS$_{2}$ is discussed. [Preview Abstract] |
|
V1.00078: Lithographically defined tapered waveguides for transformation optics device applications Todd Adams, Kurt Ermer, Alex Piazza, Dave Schaefer, Vera Smolyaninova, Igor Smolyaninov Recent progress in metamaterials and transformation optics (TO) give rise to such fascinating devices as perfect lenses, invisibility cloaks, etc., which are typically achieved with metamaterials. Realization of these devices using electromagnetic metamaterials would require sophisticated nanofabrication techniques. Recently we have demonstrated that the same effect may be achieved by much simpler means. By tapering a waveguide, one can literally ``bend'' optical space and achieve the same result. Our approach leads to much simpler designs, which require conventional lithographic techniques and readily available dielectric materials. Here we report fabrication of low cost TO devices, such as analogues of metamaterial lenses and invisibility cloaks. Their broadband properties will be demonstrated and performance for light of different polarization will be discussed. [Preview Abstract] |
|
V1.00079: Radiation rate enhancement in multilayered photonic and plasmonic nanopillars Nate Lawrence, Luca Dal Negro We have systematically studied arrays of multilayered nanopillars composed of both metal and dielectic materials and shown that they can be used to enhance the radiative properties of active materials through modification of the local density of states (LDOS). Using an extension of the multipolar expansion method in two dimensions, we are able to calculate modifications in the radiation rate of emitters and power radiated to the far field. We show multi-resonant confinement of light to sub-wavelength gap regions inside nanopillars composed of alternating layers of metal and dielectric materials, forming a circular metal-insulator-metal (MIM) device. Sub-wavelength light confinement of 1.55$\mu $m radiation is also demonstrated in purely dielectric nanopillars with reduced optical losses using alternating layers of high and low refractive index materials. In both cases, we find that the LDOS can be strongly increased, modifying the radiative rate and the internal quantum efficiency of emitters. Using top-down electron beam lithography, reactive ion etching and sputtering deposition we have created for the first time high-aspect ratio, light emitting, multilayered nanopillar structures consisting of alternating Si and Er:SiNx layers. Using dark-field scattering and photoluminescence decay spectroscopy we have experimentally characterized the fabricated nanostructures and demonstrated ability to control their radiation properties. These results are important to enable novel Si-based optical cavities and light emitting structures with nanoscale light confinement for optical communications and sensing. [Preview Abstract] |
|
V1.00080: Characterizing FeOOH Nanorice in Solution Using Polarized and Depolarized Light Scattering Phil Dee, Olga Dement'eva, Victor Rudoy, Kiril Streletzky Characterizing spindle-shaped (nanorice) particles of iron(III) oxyhydroxide (FeOOH) within their native solution environment is essential for understanding their properties for specific applications such as targeted synthesis of core/metal nano-shell structures. The combination of Dynamic Light Scattering (DLS), Static Light Scattering (SLS) and carefully designed Depolarized Dynamic Light Scattering (DDLS) allows to measure translational and rotational dynamics, structure, and size distribution of nanorice \textit{in situ}. In addition, DLS/SLS/DDLS provides sampling of a large number of nanorice particles as opposed to a few particles typically probed by the imaging techniques. The prolate ellipsoid and solid cylinder models were used to deduce FeOOH nanorice dimensions. The ellipsoidal model generally produced nanoparticle lengths and aspect ratios within 10-20{\%} of the transmission electron microscopy (TEM) results. The cylinder model performed slightly worse. The effects of number concentration of FeOOH nanoparticles in solution on their dynamics were also studied to understand the degree of coupling between the rotational and translation diffusion under different conditions. [Preview Abstract] |
|
V1.00081: Modeling of Au Nanoparticles and Semiconductor Nanowires for Nanodevice Applications A. Makepeace, J.M. Yarrison-Rice, P. Kumar, M. Fickenscher, L.M. Smith, H.E. Jackson, Y.-J Choi, G.-J. Park, C. Jagadish Semiconductor nanowires with and without plasmon enhancement are being studied for nanodevice applications ranging from chemical sensors to medical monitors and photovoltaics. Semiconductor nanowires can incorporate materials with different bandgaps and can be p- or n-doped. Growths come in different morphologies and geometries (bare, axial or radial heterostructures); all of which expands the design parameters for photocurrent based devices. When Au nanoparticles are attached to nanowires, the local electric field can be enhanced by orders of magnitude, thus increasing their absorption and photocurrent. Using an FDTD Maxwell solver, we simulate local electric fields and absorption characteristics of semiconductor nanowires and Au nanoparticles. We report on spherical, cylindrical and bipyramidal Au nanoparticles with local electric field enhancements that increase with nanoparticle asymmetry and sharp features. The Au nanoparticle modeling data is also in good agreement with experimental absorption data. Initial investigations of 275 nm InP nanowires exhibit internal mode structure under illumination with both polarizations, and absorption coefficients as a function of wavelength. These results provide insight into our experimental investigations of nanowire device applications. [Preview Abstract] |
|
V1.00082: UV Photodetectors using Vertically-aligned GaN n-core/p-shell Arrays Jong-Yoon Ha, Sergiy Krylyuk, Dipak Paramanik, Ratan Debnath, Albert V. Davydov, Matthew King, Abhishek Motayed The fabrication methods of GaN nanostructures, such as vertically aligned core-shell nano- and micro- pillar arrays, are critical for device applications. We have demonstrated dense arrays of vertically-oriented, individual GaN core-shell structures realized by a combination of top-down etching of the n-type pillars and subsequent p-shell epitaxial growth using selective CVD. The patterned samples were then etched in an inductively coupled plasma system to form GaN pillars. Mg-doped p-type GaN shells were then epitaxially grown over the n-GaN pillars in a custom-built horizontal hot-wall halide vapor phase epitaxy (HVPE) reactor. Room-temperature photoluminescence and Raman spectroscopy measurements indicate strain-relaxation in the etched pillars compared to the as-grown GaN film. Complete devices have been fabricated using dielectric planarization Detailed device characterization was correlated with TEM microstructural analysis. [Preview Abstract] |
|
V1.00083: The absorption and optical properties of nanocomposite systems Irina Bariakhtar, Yuri Demidenko, Valeri Lozovski An approach to describe the excitation and propagation of the surface plasmon polaritons along the surface with the nanodiscs that are located above it is proposed. In the framework of the proposed approach, the dissipative function is calculated for the different geometry of the systems with the discs. The Fano-like antiresonance curves of absorption profiles have been obtained. The antiresonance absorption characteristics have been explained by the interaction between the surface plasmon polariton with the continuous spectrum and localized plasmon polaritons at the nanodisks or nanocylinders with the discrete spectrum. The localized plasmon polariton can be used, for example, in solar cells for absorbing and enhancement of the solar radiation. The obtained result is similar to the well-known Fano effect. [Preview Abstract] |
|
V1.00084: Induction of Magnetization in Zig-Zag Graphene Nanoribbons by Bending Nabil Al-Aqtash, Renat Sabirianov We study the induced magnetization in the zig-zag terminated graphene nanoribbon (ZGNR) by applying strain gradient. In-plane sinusoidal gradient is shown to produce measurable magnetization localized around the location with the largest strain gradient. We discuss it from the point of view of flexomagnetic effect. By symmetry, the magnetization induction is forbidden in infinite system. However, it appears in the finite system due to the removal of the time-reversal symmetry. We performed ab initio Density Functional Theory (DFT) calculations for 4-ZGNR and show that local magnetic moments are decreased at the edges with inward curvature and increase at the edges with outward curvature. Due to antiferromagnetic arrangement of magnetization of two edges a net magnetization is induced by strain. We estimate an average magnetization of $\sim$ 3.3 $\mu$B that produced from the bending of nanoribbon with the sinusoidal profile $\delta $x$=$Asin(2$\pi $z/L) with A$=$ 3{\AA} and L$=$87.4 {\AA} (z$=$0..L/2, i.e. the half of the period). The appearance of net local magnetization is due to asymmetry of magnetic moments induced at two edges when nanoribbon is subjected to non-uniform deformation, i.e. the presence of the strain gradient. The magnetic moments vary as function of local curvature due to the charge redistribution on the curved edges. [Preview Abstract] |
|
V1.00085: Spin-Dependent Smoluchowski effect Oleg Stepanyuk, Marco Corbetta, Oleg Polyakov, Hirofumi Oka, Alexander Saletsky, Dirk Sander, Valeri Stepanyuk, J\"urgen Kirschner Surface defects, such as steps, nanoclusters, stripes or wires can significantly perturb the electronic structure of a surface. More than 70 years ago, Smoluchowski showed that electrons will not follow the sharp discontinuity of an atomic structure at step edges, instead, redistribution or ``smoothing'' of the electron cloud at surface protrusions should occur [1]. A charge redistribution process involves charge flow from the top of the step to the bottom and results in formation of local dipoles that are antiparallel to the surface dipoles of flat surfaces. We present a combined ab initio and experimental study of spin-dependent effects at the edges of magnetic nanoislands. Our results give clear evidence of the existence of a spin-dependent Smoluchowski effect which leads to spin, spatial and energy dependent charge flow at surface corrugations. Striking changes in the spin-polarization at the edge of Co islands on Cu(111) are predicted by calculations and revealed by the spin-polarized STS. We concentrate on a single Co nanoislands on Cu(111)[2]. Our results demonstrate that the spin-dependent Smoluchowski effect can strongly influence the tunneling magnetoresistance at the edges of magnetic nanostructures on metal surfaces. \\[4pt] [1] R. Smoluchowski, Phy. Rev. 60, 661 (1941)\\[0pt] [2] H. Oka et. al., Science 327, 843 (2010)\\[0pt] [3] O.P. Polyakov, et.al., Phys. Rev. B, accepted (2012) [Preview Abstract] |
|
V1.00086: Fabrication of Submicron Devices on the (011) Cleave Surface of a Cleaved-Edge-Overgrowth GaAs/AlGaAs Crystal Hao Zhang, Loren Pfeiffer, Kenneth West, Albert Chang We describe the fabrication of submicron devices on the (011)cleave surface of a GaAs heterostructure crystal, in which this surface is extremely narrow. Special purpose devices are produced, which take advantage of the unique characteristics of Cleaved-Edge-Overgrowth. The successful fabrication relies on understanding the surface tension of the electron beam PMMA resist, the workable degree of variation in resist thickness, and on gluing the crystal onto a backing substrate to increase structural strength. We demonstrate a functional gate-controlled point contact constriction placed 9 um from one edge of the cleave surface. This technique may enable the study of fractional quantum Hall fluid in a novel structure. [Preview Abstract] |
|
V1.00087: Vibrational mode mediated electron transport in molecular transistors Deborah Santamore, Neill Lambert, Franco Nori We investigate the steady-state electronic transport through a suspended dimer molecule coupled to leads. When strongly coupled to a vibrational mode, the electron transport is enhanced at the phonon resonant frequency and higher-order resonances. The temperature and bias determines the nature of the phonon-assisted resonances, with clear absorption and emission peaks. The strong coupling also induces a Frank-Condon-like blockade, suppressing the current between the resonances. We compare an analytical polaron transformation method to two exact numerical methods: the Hierarchy equations of motion and an exact diagonalization in the Fock basis. In the steady-state, our two numerical results are an exact match and qualitatively reflect the main features of the polaron treatment. Our results also indicate the possibility of compensating the current decrease due to the thermal environment. [Preview Abstract] |
|
V1.00088: Propagation of long-lifetime polaritons in a semiconductor microcavity German V. Kolmakov, Oleg L. Berman, Roman Ya. Kezerashvili We study propagation of polaritons in a high-quality microcavity. The polaritons are formed by the cavity photons coupled with the excitons in a semiconductor quantum well. We focus on the long-lifetime polaritons ($\sim$~100 ps), which can spread in a semiconductor structure over a few mm distance before they damp. The case where the polaritons form a non-equilibrium Bose-Einstein condensate is considered. We discuss the changes in the spatial polariton distribution if the polaritons are accelerated by a constant force in the wedge-shaped microcavity. [Preview Abstract] |
|
V1.00089: Characterization of patterns produced by AFM Nano-Lithography on thin films of Lanthanum Barium Manganese Oxide, La$_{0.7}$Ba$_{0.3}$MnO$_3$ E. Kevin Tanyi, Parul Srivastava, Christopher Stumpf, Kevin Schenning, Tyler Goehringer, Rajeswari Kolagani, David Schaefer AFM Nano-lithography is a process that uses a bias voltage between the tip of an atomic force microscope (AFM) and a sample placed beneath the tip, to produce patterns on the sample through electro-chemically induced surface modification. AFM nanolithography has been demonstrated on Silicon as well as on thin films of several perovskite metal oxides. Most of the previous research in AFM nanolithography on thin films has focused on the effects of humidity, tip voltage, contact force and the scan rate on the nanolithography processes. Little attention has been paid to the possible role of substrates on which these films have been grown. We have observed that the substrate characteristics (type of substrate, substrate thickness and surface termination) have an impact on the characteristics of the patterns produced by AFM nanolithography. In this work, we present nanolithography studies on (100) SrTiO3 (alias STO) and (100) silicon substrates before and after the deposition of thin films of La$_{0.7}$Ba$_{0.3}$MnO$_{3}$ (LBMO). The characteristics of the patterns produced will be discussed in an effort to fully understand how the patterns depend on sample thickness (substrate or film), sample composition (STO, Si, LBMO), voltage and scan rate. Analysis of these results is expected to shed light on the chemical and physical changes responsible for AFM nanolithography. [Preview Abstract] |
|
V1.00090: Nanoscale Effects on Charge Transport due to Surface-Plasmon Induced Quantum Image Forces Charles Cherqui, Andrei Piryatinski, David Dunlap We examine the motion of a charge carrier in a carbon nanotube in the presence of a metal nanosphere. We show that the system can be reduced to that of a free particle moving in an effective potential consisting of a classical attractive image potential and a repulsive quantum correction. Charge carrier transport in this representation results in a resonance tunneling through the effective potential. We analyze the transmtion coefficent as a function of distance from the surface of the metal nanoparticle to the nanotube. This device setup could be used as the basis for a nanoscale filed effect transitor. [Preview Abstract] |
|
V1.00091: Ab initio investigation of thermoelectric properties of AlN nanowires under axial stress George Alexandru Nemnes, Tudor Luca Mitran, Adela Nicolaev, Camelia Visan, Lucian Ion, Stefan Antohe Small diameter nanowires, down to a few lattice constants, are structurally and electronically different from bulk, due to the large surface-to-volume ratio and the effects of the surface states, which has consequences in the optical absorption and in the electrical/thermal transport. It has been recently established that AlN nanowires can suffer a stress induced phase transition from a wurtzite to a graphite-like phase [1]. The thermopower of atomic-sized wurtzite AlN wires coupled to Al(111) bulk contacts is investigated at low temperatures using Green-Keldysh formalism. We ?nd that the conduction of the wide bandgap semiconductor wire is essentially enhanced by the presence of surface states. We show that the evanescent coupling to the surface states is strong enough to render thermopower of a few tens of micro-V/K, which may be enhanced by controlling the position of the surface states. [2]. We also investigate the changes in the thermopower under applied axial stress, comparatively analyzing the nanowires in the wurtzite and graphite-like configurations. [1] T.L. Mitran, Adela Nicolaev, G.A. Nemnes, L. Ion, S. Antohe, Comput. Mat. Sci. 50, 2955 (2011) [2] G.A. Nemnes, C. Visan, S. Antohe, Physica E 44, 1092 (2012) [Preview Abstract] |
|
V1.00092: Nanoscale Phonon Transport as Probed with a Microfabricated Phonon Spectrometer for the Study of Nanoscale Energy Transport Richard Robinson, Obafemi Otelaja, Jared Hertzberg, Mahmut Aksit, Derek Stewart Phonons are the dominant heat carriers in dielectrics and a clear understanding of their behavior at the nanoscale is important for the development of efficient thermoelectric devices. In this work we show how acoustic phonon transport can be directly probed by the generation and detection of non-equilibrium phonons in microscale and nanoscale structures. Our technique employs a scalable method of fabricating phonon generators and detectors by forming Al-Al$_{\mathrm{x}}$O$_{\mathrm{y}}$-Al superconducting tunnel junctions on the sidewalls of a silicon mesa etched with KOH and an operating temperature of 0.3K [1]. In the line-of-sight path along the width of these mesas, phonons with frequency $\sim$100 GHz can propagate ballistically The phonons radiate into the mesa and are observed by the detector after passing through the mesa. We fabricated silicon nanosheets of width 100 to 300 nm along the ballistic path and observe surface scattering effects on phonon transmission when the characteristic length scale of a material is less than the phonon mean free path. We compare our results to the Casimir-Ziman theory. Our methods can be adapted for studying phonon transport in other nanostructures and will improve the understanding of phonon contribution to thermal transport. The work was supported in part by the National Science Foundation under Agreement No. DMR-1149036.\\[4pt] [1] J. B. Hertzberg et al, Rev. Sci. Inst. 82, 104905 (2011). [Preview Abstract] |
|
V1.00093: Phonon Engineering of ZnO nanowires with controlled chemical doping Jaime Bohorquez-Ballen, Thushari Jayasekera Using the first principles density functional theory (DFT) calculations, we have investigated electronic and dynamical properties of ZnO nanowires in [001] direction with different diameters in the presence of impurities such as Mg, Al, and Ga.~ As the impurity concentration is varied, electrical and thermal conductivities of nanowires change. In this way, nanowires can be engineered to reduce the thermal transport, such that their thermoelectric properties can be enhanced. [Preview Abstract] |
|
V1.00094: Thermoelectric properties of the ReCN A. Reyes-Serrato, Jorge Sofo We present thermoelectric properties of the new material, ReCN. Combining first principles band structure calculation with semi classical model analysis; we obtained the Seebeck coefficient as well as the electrical conductivity as a function of the relaxation time for the electrons. The results indicate the potential of the ReCN as a good thermoelectric material in the low region of the temperature. [Preview Abstract] |
|
V1.00095: III/V Nanowire-based Devices for Thermoelectrics Valentina Troncale, Philipp Mensch, Siegfried Karg, Heinz Schmid, Pratyush Das Kanungo, Emanuel Loertscher, Ute Drechsler, Volker Schmidt, Heike Riel, Bernd Gotsmann The thermo-physical properties of one-dimensional semiconductor nanostructures make them suitable for high ZT thermoelectric devices. Theoretical studies indicate that III/V nanowires (NWs) are eligible for ZT enhancement, due to increased phonon scattering resulting in thermal conductivity (k) suppression, without affecting the electrical conductivity (s). We address the thermoelectric properties of III/As NWs grown by selective-area MOVPE on Si (111) substrates, transferred onto micro-fabricated MEMS-based devices, optimized for direct thermal transfer measurements. The NWs were positioned across the gap between adjacent symmetric SiNx membranes, structured on Si. Platinum resistive heaters/thermometers connected to leads, and contacts to the NWs were realized by electron beam lithography and lift-off technique. The structures were then under-etched. For InAs NWs, we compared the k measured by both the direct method and the self-heating technique. Heat loss to the substrate and contact resistance were evaluated by finite elements simulations and compared for different fabrication techniques. We discuss alternative solutions to the technical challenge of precise NW positioning. [Preview Abstract] |
|
V1.00096: Electronic Structure and Thermoelectric properties of (LaO)x(MCh)y Hiroki Funashima, Hiroshi Katayama-Yoshida (LaO)MCh (M=Cu,Ag,Au, Ch=S,Se,Te) are known as transparent narrow gap p-type semiconductor, which give an excitonic absorption/emission near the band edge even at room temperature. These compounds have P4/nmm structure and can oxide natural superlattice semiconductor. In this paper at first, we calculated band structure for these compounds, using FLAPW based on LDA/DFT. In our results, these compounds have large anisotropy $k_{z}$ direction. On $\Lambda$, $V$, and $W$ axises, dispersion curves are very flat. W analyze the electronic structure by group theory. Secondly, we calculated conductivity tensor and Seebeck coefficient using Bloch-Boltzmann Equation semi-classically. Bloch-Boltzmann equation shows that in small dispersion so-called flat band structure, shape of Fermi-surface increase as temperature increase, dramatically, in the result these compounds have large Seebeck-coefficient. As mentioned, we showed that because these compounds have flat-band structure in a direction toward $k_{z}$, these compounds have large Seebeck coefficient. At the same time, these compounds have a small hole-pocket in valence band, thus these compounds have good electric conductivity. Finally, we changed chalcogen Ch(=S, Se,Te) and will suggest new-generation high-efficie [Preview Abstract] |
|
V1.00097: Approach to Exchange Bias Effect in La$_{2/3}$Ca$_{1/3}$MnO$_{3}$/BiFeO$_{3}$ and BiFeO$_{3}$/ La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ Bilayers Claribel Dominguez, John E. Ordonez, Sandra Diez, Maria E. Gomez, Stefan Gu\'enon, Ivan K. Schuller We have grown bilayers of ferromagnetic La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ (LCMO) and multiferroic BiFeO$_{3}$ (BFO) on (100) SrTiO$_{3}$ (STO) substrates, by DC- and magnetron RF -sputtering technique, respectively, at high-oxygen pressures. We maintain constant the thickness of the layers (t$_{BFO}$=72nm; t$_{LCMO}$=80nm). Temperature dependence of the resistivity indicates that the MI-transition temperature of the manganite in the BFO/LCMO/STO is affected by the presence of the BFO layer in comparison with T$_{MI}$ for the single LCMO layer. Furthermore, temperature dependence of magnetization shows that the BFO/LCMO/STO bilayer has higher Curie temperature than that for LCMO/BFO/STO, indicating a strong structural dependence of the LCMO layer with magnetic response. The dependence of the magnetic moment with magnetic field after field cooling gives indication of the existence of Exchange Bias effect in the LCMO/BFO/STO bilayer. Isothermal loops also display dependence of the Exchange Bias magnitude with field cooling. [Preview Abstract] |
|
V1.00098: ABSTRACT WITHDRAWN |
|
V1.00099: ABSTRACT WITHDRAWN |
|
V1.00100: Electronic structure of catalytically active gold clusters supported on cerium oxide Neil Lawrence, Yunyun Zhou, Joseph Brewer, Vivianna Lawrence, Chin Li Cheung, Yi Gao, Xiao Cheng Zeng, Lu Wang, Wai-Ning Mei, Renat Sabirianov, Lingmei Kong, Jing Liu, Peter Dowben, Tai-Sing Wu, Yun-Liang Soo The high catalytic activity of gold nanoclusters when compared to that of the bulk counterpart has been an intensively-studied phenomenon using both chemical and computational experiments in the last two decades. Due to the complexity of these systems and their size- and substrate-dependent activities, different explanations discussed in the literature for these unusual activities are still under debate. Since all these proposed reasons can lead to changes in the electronic structures of the resulting gold clusters, it is necessary to resolve the details of these potential changes in catalytically active systems. Here we report our findings on some features in the electronic structures of catalytically active gold clusters supported on cerium oxide investigated by resonance photoemission spectroscopy. Particularly, the d-band of the examined gold clusters was found to be incompletely filled. These results corroborate the computed electronic structures of our computed planar and non-planar gold cluster models on cerium oxide support. [Preview Abstract] |
|
V1.00101: Dimensional crossover of a fermion gas within periodic structures Patricia Salas, M.A. Solis We report the thermodynamic properties of an interactionless Fermi gas immersed in periodic structures such as penetrable multilayers or multitubes created by one (planes) or two perpendicular (tubes) external Dirac comb potentials, allowing fermions to move freely in the remaining directions. The chemical potential $\mu$, as a function of temperature and of the planes impenetrability $P_0$, shows a anomalous behavior when the tubes wall impenetrability reaches a critical value while keeping the cross section constant. The specific heat of fermions inside tubes, as a function of temperature, shows two very noticeable dimensional crossovers as the system behavior goes from 3D to 2D and latter to 1D as $P_0$ is increased. [Preview Abstract] |
|
V1.00102: ABSTRACT WITHDRAWN |
|
V1.00103: Landau Quantization of a 2D Antidot Lattice N.J.M. Horing, S. Bahrami, Vassilios Fessatidis We derive the Schr\"{o}dinger eigen-energy dispersion relation for a two dimensional sheet of electrons in a one dimensional periodic lattice of quantum antidot potential barriers, with a perpendicular quantizing magnetic field. This system is in the nature of a Kr\"{o}nig-Penney model with a high magnetic field present and we construct the appropriate Green's function which we use to formulate the dispersion relation for the energy spectrum. [Preview Abstract] |
|
V1.00104: Landau Quantization of an Asymmetric Double-Quantum-Dot N.J.M. Horing, S.L. Horton, V. Fessatidis We examine the subband energy eigenstates of a two-dimensional asymmetric quantum double-dot system embedded in a two dimensional host sheet subject to Landau quantization. The dispersion relation for the asymmetric quantum double-dot subband energies is formulated and examined by analyzing the frequency poles of the appropriate Green's function with Landau-quantization-like splintering of the levels by a magnetic field. The effects of the asymmetry of the quantum dots in regard to their potential well depths are analyzed as functions of the well depth difference and dot separation. [Preview Abstract] |
|
V1.00105: Magnetotransport Properties of Co$_2$FeAl Nanowires Keshab R. Sapkota, P. Gyawali, Bishnu Dahal, R. Dulal, I.L. Pegg, John Philip Co$_2$FeAl (CFA) nanowire (NW) exhibit interesting magnetic behavior with temperature, which arises from the granular structure.\footnote{Keshab R Sapkota \textit{et.al,} J. Appl. Phys.~Vol. \textbf{111}, Issue 12, 123906 (2012); http://dx.doi.org/10.1063/1.4729807} To understand the magnetotransport properties, single CFA NW devices were fabricated using standard electron beam lithography. The magnetoresistance measurements of single CFA NW device were carried out at different temperatures. The magnetoresistance measurements show oscillations as a function of applied external magnetic field. [Preview Abstract] |
|
V1.00106: Electron-Energy-Loss Spectra of Free-Standing Silicene Luis M. Priede, Lilia Meza-Montes, E. Gomez-Barojas Silicene, the silicon-based counterpart of graphene, is increasingly getting attention because it is a semi-metal material with Dirac cones and thus, in principle, has similar electronic properties [1, 2]. In this work we calculated the Electron Energy Loss Spectrum (EELS) of ideal free-standing silicene. Dielectric function is obtained by using a discretization method as suggested by Delerue, et al. [3]. Tight-binding method is applied considering 2nd Nearest Neighbors with $sp^2$ orbitals, the Slater-Koster parameterization [4] and the Harrison's rule. This has been done for plane and buckled silicon sheets, in the latter case with a structure based on DFT calculations [2]. The resulting dielectric function is compared to those of bulk silicon and graphene. Spectra of EEELS are contrasted for plane and buckled silicene, particularly the plasmon frequency as a function of the $z$ displacement of buckled silicene.\\[4pt] [1] S. Leb\`egue and O. Eriksson, Phys. Rev. B 79, 115409 (2009).\\[0pt] [2] S. Cahangirov, et al., Phys. Rev. Lett. 102, 236804 (2009).\\[0pt] [3] C. Delerue, et al., Phys. Rev. B 56, 15306 (1997).\\[0pt] [4] G. G. Guzm\'an-Verri and L. C. Lew Yan Voon, Phys. Rev. B 76, 075131 (2007). [Preview Abstract] |
|
V1.00107: Elementary electronic excitations in quantum wires made up of vertically stacked quantum dots M.S. Kushwaha We report on the theoretical investigation of the elementary electronic excitations in a quantum wires made up of vertically stacked self-assembled InAs/GaAs quantum dots. The resultant quantum wire is characterized by a two-dimensional harmonic confining potential in the x-y plane and a periodic (Kronig-Penney) potential along the z (or the growth) direction within the tight-binding approximation. Since the wells and barriers are formed from two different materials, we employ the Bastard's boundary conditions in order to determine the eigenfunctions along the z direction. These wave functions are then used to generate the Wannier functions, which, in turn, constitute the legitimate Bloch functions that govern the electron dynamics along the direction of periodicity. Thus the Bloch functions and the Hermite functions together characterize the whole system. We discuss the behavior of the eigenfunctions, band-widths, density of states, Fermi energy, single-particle and collective excitations, and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier- and well-widths can allow us to tailor the excitation spectrum in the desired energy range... [Preview Abstract] |
|
V1.00108: Heavy-hole light-hole mixing mechanisms and optical polarization in semiconductor QDs Alex Zunger, Gabriel Bester, Jun-Wei Luo The symmetry of epitaxially grown semiconductor QDs was often overestimated to be D$_{2d}$ in which case the [110] and [1-10] directions are equivalent. Under D$_{2d}$ symmetry the underlying bulk HH and LH states belong to two different irreducible representations, $\Gamma _{7}$ and $\Gamma_{6}$ respectively, forbidding HH-LH mixing. Experimentally found HH-LH mixing in strained InAs/GaAs QDs was attributed to symmetry breaking induced by strain. In strain-free GaAs/AlGaAs QDs, one expects such HH-LH mixing to be vanishing. However, the HH-LH mixing experimentally observed in strain-free GaAs/AlGaAs QDs is comparable with the one observed in strained InAs/GaAs QDs. The origin of this mixing was assumed to originate from dot shape anisotropy. Using the atomistic pseudopotential method we find that the HH-LH mixing exists even in overall shape symmetric strain-free GaAs/AlGaAs QDs with a magnitude even larger than in the case of strained InAs/GaAs QDs. We will analyze the relative importance of the following mechanisms: (i) the intrinsic nonequivalence of the [110] and [1-10] directions, which lowers the QDs symmetry to C$_{\mathrm{2v}}$; (ii) shape anisotropy induced symmetry breaking; (iii) built-in non-uniform strain; (iv) alloying effects in either dot material or dot barrier, and (v) C$_{\mathrm{2v}}$ interfaces in QDs. We also demonstrated that the intrinsic crystal induced optical anisotropy could be washed out by other factors, such as dot shape anisotropy, which indicates that HH-LH mixing is not the only mechanism responsible for optical anisotropy. [Preview Abstract] |
|
V1.00109: Sub-250nm room temperature optical gain from AlGaN materials with strong compositional fluctuations Emanuele Francesco Pecora, Wei Zhang, Haiding Sun, A. Yu. Nikiforov, Jian Yin, Roberto Paiella, Theodore D. Moustakas, Luca Dal Negro Compact and portable deep-UV LEDs and laser sources are needed for a number of engineering applications including optical communications, gas sensing, biochemical agent detection, disinfection, biotechnology and medical diagnostics. We investigate the deep-UV optical emission and gain properties of Al$_{\mathrm{x}}$Ga$_{\mathrm{1-x}}$N/Al$_{\mathrm{y}}$Ga$_{\mathrm{1-y}}$N multiple quantum wells structure. These structures were grown by molecular-beam epitaxy on 6H-SiC substrates resulting in either homogeneous wells or various degrees of band-structure compositional fluctuations in the form of cluster-like features within the wells. We measured the TE-polarized amplified spontaneous emission in the sample with cluster-like features and quantified the optical absorption/gain coefficients and gain spectra by the Variable Stripe Length (VSL) technique under ultrafast optical pumping. We report blue-shift and narrowing of the emission, VSL traces, gain spectra, polarization studies, and the validity of the Schalow--Townes relation to demonstrate a maximum net modal gain of 120 cm$^{-1}$ at 250 nm in the sample with strong compositional fluctuations. Moreover, we measure a very low gain threshold (15 $\mu$J/cm$^{2})$. On the other hand, we found that samples with homogeneous quantum wells lead to absorption only. In addition, we report gain measurements in graded-index-separate-confined heterostructure (GRINSCH) designed to increase the device optical confinement factor. [Preview Abstract] |
|
V1.00110: UV-VIS regime band gap in a 3-d photonic system Ming Yin, Fouzi Arammash, Timir Datta, Ray Tsu Synthetic opals are self-organized bulk, close packed systems that are three-dimensionally ordered with periodicity determined by the sphere diameter. These materials have been used as templates for nano devices with novel properties. For example, in carbon inverse opals show quantum hall effect and related magneto electric responses. Inverse are also reported to show photonic band gap. It is expected that devices based on these materials will be an alternative to electronic devices. These opal specimens were hexagonal or face centered cubic crystals with silica sphere diameter ranging between 220 nm and 270nm. Here we will present results of structural and imaging studies such as SEM, AFM and XRD. In addition results of the (UV-VIS) optical behavior will be provided. The optical response will be analyzed in terms of photonic band gaps in the sub-micrometer optical and UV regime. [Preview Abstract] |
|
V1.00111: Optical absorption of magnesium nanoblades George Marshall, Ken Podolak Hydrogen cars are not widely distributed due primarily because there are no viable options for long term storage. Magnesium nanoblades may solve this problem, which are smaller than the width of a human hair. These formations can potentially store more than double the amount of hydrogen than current standards. Nanoblades are unique due to their rechargeable nature, which allows it to store and release hydrogen over wide temperature ranges. Also, there is a large surface area which allows a maximum amount of hydrogen to store. In advancement of this field, I examined how visible light interacted with the nanoblades over the entire angular spectrum. This experiment successfully developed a relationship between the angle of light's approach and the nanoblade's absorption of the light, indicating the deposited angle of the nanoblade influences the nanoblade's optical properties. This experiment proves light can be used as a mechanism to store/release hydrogen from the nanoblades, providing a possible energy efficient method to make hydrogen storage more cost effective. [Preview Abstract] |
|
V1.00112: Dynamical changes in plasmon behavior of transition metal alloys Ken Podolak, Jamie Smith, Daniel Stowe A plasmon is as a ray of light bound onto a surface of a conducting metal, propagating among the surface and presenting itself as an electromagnetic field. The ability to control or manipulate these plasmons in subwavelength volumes is recently become of interest to improve functionality and performance of optical devices. Furthermore, plasmons can be used to monitor interactions in a biospecific surface on a metal layer. The plasmon waves of light occur at the interface between the metal and dielectric, measurable by absorption peaks in the UV or visible light. A thin top layer of gold or copper are utilized with alloys of metals underneath composed of nickel, iron, or manganese. A Cary-OLIS spectrophotometer measures the optical absorption of these samples where surface and bulk plasmon energy peaks are identified. The full width half maximum of the plasmon peaks appears to broaden over a range of alloys, which represents a change in the strength of the resonance. Further discussion of this will be presented. [ref] K.R. Podolak, S.B. Wagner, and J.A. Smith, ``Manganese doping influence on the plasmon energy of nickel films,'' Surface Science 606, 996 (2012). [Preview Abstract] |
|
V1.00113: Hermitian Two-band Model for One-dimensional Plasmonic Crystals Yuji Kitamura, Shuichi Murakami Surface plasmon polaritons form band structure when the metal surface is periodically corrugated. Such a microscopic structure of metal surface is called the plasmonic crystal. We theoretically study the plasmonic band structure of 1D plasmonic crystals. Although a similar work was reported previously, the eigenvalue equation is non-hermitian. Such a non-hermitian eigenvalue equation has essential difficulties because their eigenvalues may be complex, and we cannot apply the perturbation theory. To avoid such difficulties, we started from the plane wave solution of the Maxwell's equation and consider the small corrugation as a perturbation to the lowest two bands. In this manner, the eigenvalue equation is derived from the matching conditions for electromagnetic fields at the interface. We show that the derived eigen equation is hermitian and analogous to the usual two-band model for electrons. We also show that the wave number and corrugation dependences of the solution behave like the band theory of electrons in solids. [Preview Abstract] |
|
V1.00114: Electronic and optical properties of TiN$_{\mathrm{x}}$ from first-principles calculations Faisal Mehmood, Ruth Pachter We present a systematic study of the structural, electronic and optical properties of bulk phases of TiN$_{\mathrm{x}}$ and its (111) surface for mimicking thin films, which are of interest technological in applications such as coatings. Time-dependent density functional theory and the GW approximation have been applied. In the first stage, a comparison between experimental ellipsometry data and the calculated optical absorption spectra, for example, for a surface upon changing stoichiometry, has been undertaken. The results demonstrate applicability of the methods in prediction of optical excitations for titanium nitride thin film, deposited with varying nitrogen flow rates. [Preview Abstract] |
|
V1.00115: Current and shot noise of a QPC coupled to an oscillator Nikhilesh Vaidya, Deborah Santamore We study the dynamics and noise power spectrum of a quantum point contact (QPC), which is coupled to a vibration mode. We obtain the non-Markovian unconditional master equation for the reduced density matrix of the system. Using both the analytical and numerical quasi-Monte Carlo method, we calculate the current through. The modified current due to the QPC-oscillator coupling consists of the terms that depend on the oscillator variables, namely, position, momentum and their moments. We find that one of the current terms, which arise from the symmetrized product of the position and momentum operators of the oscillator, has a substantial contribution to the total current in the non-Markovian case. Both the current and the equations of motion of the oscillator reduce to the Markovian forms under the appropriate limits, namely, the long time limit, which makes the coefficients time independent, and the wide band limit. We also calculate the spectral density of the coupled system. The noise spectra show that the resonant peaks depict the backaction between the QPC and the oscillator. The interplay between the noise and the backaction may have some practical applications such as amplification of the oscillators. Our results agree with the experimental evidence. [Preview Abstract] |
|
V1.00116: Fabrication of nanoporous TiO2 filters using organic--inorganic nanocomposites Mehmet Burak Kaynar, Ryan DelPercio, Emre Yassitepe, Sadan Ozcan, S. Ismat Shah Nanoporous TiO2 filters with 50 nm mean pore size is synthesized by using commercial TiO2 nanoparticles and polyvinylpyrrolidone with an easy and low cost route that did not involve any solvent. Crystal's structure and surface morphologies are studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. X-ray photoelectron microscopy (XPS) is used to confirm the filtering process by analyzing pre- and post-filter affluent containing nanoparticles to simulate the filtration of micrometer (bacteria) and nanometer (virus) species. Greater than 85{\%} filtering efficiency is obtained during the filtering of a mixture of water and 30 nm mean crystallite size of iron oxide nanoparticles. [Preview Abstract] |
|
V1.00117: Second-harmonic generation in substoichiometric silicon nitride layers Emanuele Francesco Pecora, Antonio Capretti, Giovanni Miano, Luca Dal Negro Harmonic generation in optical circuits offers the possibility to integrate wavelength converters, light amplifiers, lasers, and multiple optical signal processing devices with electronic components. Bulk silicon has a negligible second-order nonlinear optical susceptibility owing to its crystal centrosymmetry. Silicon nitride has its place in the microelectronic industry as an insulator and chemical barrier. In this work, we propose to take advantage of silicon excess in silicon nitride to increase the Second Harmonic Generation (SHG) efficiency. Thin films have been grown by reactive magnetron sputtering and their nonlinear optical properties have been studied by femtosecond pumping over a wide range of excitation wavelengths, silicon nitride stoichiometry and thermal processes. We demonstrate SHG in the visible range (375 - 450 nm) using a tunable 150 fs Ti:sapphire laser, and we optimize the SH emission at a silicon excess of 46 at.{\%} demonstrating a maximum SHG efficiency of 4x10$^{\mathrm{-6}}$ in optimized films. Polarization properties, generation efficiency, and the second order nonlinear optical susceptibility are measured for all the investigated samples and discussed in terms of an effective theoretical model. Our findings show that the large nonlinear optical response demonstrated in optimized Si-rich silicon nitride materials can be utilized for the engineering of nonlinear optical functions and devices on a Si chip. [Preview Abstract] |
|
V1.00118: Irreversibility and carriers control in two-dimensional electron gas at LaTiO$_{3}$/SrTiO$_{3}$ interface N. Bergeal, J. Biscaras, S. Hurand, C. Feuillet-Palma, J. Lesueur, A. Rastogi, R.C. Budhani, N. Reyren, E. Lesne, D. Leboeuf, C. Proust It has been shown recently that a two-dimensional electron gas 2DEG could form at the interface of two insulators such as LaAlO$_{3}$ and SrTiO$_{3}$ [1], or LaTiO$_{3}$ (a Mott insulator) and SrTiO$_{3}$ [2-3]. We present low temperature transport measurements on LaTiO$_{3}$/SrTiO$_{3}$ and LaAlO$_{3}$/SrTiO$_{3}$ hetero-structures, whose properties can be modulated by field effect using a metallic gate on the back of the substrate [4]. Here we show that when the carrier density is electrostatically increased beyond a critical value, the added electrons escape into the SrTiO$_{3}$ leading to an irreversible doping regime where all the electronic properties of the 2DEG saturate (carrier density, resistivity, superconducting transition...). The dynamic of leakage was studied using time resolved measurement. Based on a complete self-consistent description of the confinement well, a thermal model for the carriers escape has been developed, which quantitatively accounts for the data [5].\\[4pt] [1] N. Reyren et al, Science 317, 1196 (2007)\\[0pt] [2] A. Ohtomo et al, Nature 419, 378 (2002)\\[0pt] [3] J. Biscaras et al, Nature Communications 1,89 (2010) \\[0pt] [4] J. Biscaras et al, Phys. Rev. Lett. 108, 247004 (2012)\\[0pt] [5] J. Biscaras et al, arXiv:1206.1198 [Preview Abstract] |
|
V1.00119: MAGNETISM II |
|
V1.00120: Origin of martensitic transition in NiMnIn alloys Renat Sabirianov, Nabil Al-Aqtash, Le Zhang, Andrei Sokolov We have performed density functional theory calculationsof the effect of the martensitic transition on the electronic structure of Ni$_{\mathrm{2}}$MnIn system. We find that both the cubic and tetragonally distorted (martensite) phases are ferromagnetic. The cubic phase has lower total energy than that of the tetragonal phase by $\Delta $E$=$0.3eV/f.u. Larger relative concentration of Mn in Ni$_{2}$Mn$_{1.5}$In$_{0.5}$ change the relative stability in favor of martensitic phase. Calculated local magnetic moment is 3.2$\mu_{\mathrm{B}}$ for Mn, while only 0.3$\mu_{\mathrm{B}}$ for Ni. The total minority densities of states exhibit a pronounced feature at Fermi level (related mainly to Ni3d states) that is sensitive to the local environment of Ni sites. The increase of the Mn content, where Mn substitutes for In sites and orders antiferromagnetically to the magnetization of the regular Mn sites, causes substantial modification in N(E$_{\mathrm{F}})$ affecting the transport properties upon the phase transition.The band structure analysis reveals that the tetragonal distortion changes the Fermi velocity at the Fermi level that may result in substantial change in resistance upon martensitic transition. We compare our results with the magnetic and transport measurements performed on the thin films of Ni$_{50}$Mn$_{35}$In$_{15}$ grown by laser-assisted molecular beam epitaxy deposition. Magnetic and transport measurements reveal the existence of martensite-austenite phase transition on tensile stressed films and co-existance of both phases at room temperature for compressively strained films. Thin films and experimental results were obtained in close collaboration with group of N. Ali, SIUC. [Preview Abstract] |
|
V1.00121: Calculated Magnetic Properties of Zigzag Boron Nitride Nanoribbon J. Rufinus Substantial theoretical and experimental efforts have been made in the quest to find the candidates for future spintronics devices. Recently, the search for new spintronics materials has also included two-dimensional graphene-based materials due to the theoretical prediction that this type of material may show the half-metallic property. We present the results of an ab-initio density functional theory within a generalized gradient approximation study of zigzag Boron Nitride Nanoribbon (ZBNNR). Our results show different magnetic orderings. However, we found that, in general, narrow zigzag BN nanoribbon prefers a magnetic state depending on the shape and thus the orientation of the atoms on its edges. These results are especially noticeable for very narrow ZBNNR. [Preview Abstract] |
|
V1.00122: Temperature Dependence of Magnetic Nanoparticles for Metamaterials Quincy Williams, Natalia Noginova, Pagnagiotis Dallas, Emmanuel Giannelis Commonly, metamaterials are systems with engineered electric response, based on optimized spatial arrangement of sub-wavelength sized metal and dielectric components. We explore alternative methods based on use of magnetic inclusions, such as magnetic nanoparticles, which can allow microwave permeability of a composite to be tuned from negative to positive at the range of magnetic resonance. Several systems with magnetic nanoparticles of different size were experimentally tested for estimate their potential as building blocks for metamaterials. Magnetic resonance studies were performed in the limits of diluted non-interacting solutions of superparamagnetic nanoparticles in liquid form and high concentrations of particles in solids at different temperatures. Broadening of the EMR signal was observed upon~increase in the particle size and concentration, due to effects of anisotropy and dipolar interaction. Microwave permeability was estimated in solid composites. In dense systems with 5 nm~iron oxide nanoparticles it can be tuned from --0.8 to 2 by the external magnetic field. [Preview Abstract] |
|
V1.00123: Micromagnetic studies of Full Huesler alloy, Co2FeAl, nanostructures Patricia Yoritomo, Nicholas Mecholsky, Parshu Gyawali, Keshab Sapkota, I.L Pegg, John Philip Co2FeAl (CFA) is a full Huesler alloy with interesting magnetic behavior and very high Curie temperature. We have carried out micromagnetic simulations on CFA nanopillars using a program, NMAG, with various dimensions and spacing. The micromagnetic simulations are compared with the experimental results that we have obtained. Nanopillars are produced using the liftoff technique after electron beam lithography. The CFA nanopillars are grown using electron beam deposition of Co, Fe and Al in the stoichiometric ratio and by further annealing at 850 K for one hour. We have simulated the magnetic behavior of CFA nanopillars ranging from 30 to 90 nm in diameter and with a height of about 115 nm. Preliminary results show the simulated coercivities are 700 Oe and 2400 Oe for 60 and 30 nm pillars. These are comparable to the experimental results that we have obtained. Magnetic behavior of polycrystalline nanowires of varying diameters is also simulated using NMAG. We will present the simulation and experimental results of nanopillars and polycrystalline nanowires in detail. [Preview Abstract] |
|
V1.00124: Evidence for Multicritical Behavior in Nanostructured Mn-intercalated TaS$_2$ Paul Shand, Corey Cooling, Zachary Griffith, Timothy Kidd, Laura Strauss Nanostructured Mn-intercalated TaS$_2$ was prepared with a nominal Mn concentration of 25{\%}. The sample consisted of nanotube structures with diameters between 30 nm and 300 nm. X-ray diffraction measurements indicated that the Mn was incorporated into intercalation sites between the TaS$_2$ layers. The sample exhibited Curie-Weiss behavior virtually all the way down to the Curie-Weiss temperature of 91 K, demonstrating the absence of significant chemical clustering and short-range order in the paramagnetic regime. Magnetization versus temperature measurements indicated a ferromagnetic transition at $\sim$90 K, which is somewhat higher than that for bulk crystalline Mn$_{0.25}$TaS$_2$. An Arrott plot confirms the ferromagnetic transition at 87 K, with critical exponents close to mean-field values. However, ac susceptibility measurements in the presence of a dc bias field suggest the presence of another transition at 81 K, with critical exponents much larger than mean-field values. A scaling plot using these unusual exponents exhibited excellent collapse of the data. We interpret this behavior in terms of a nearby multicritical point, with the system exhibiting re-entrant cluster-glass behavior. [Preview Abstract] |
|
V1.00125: Tuning Magnetism and Electronic Phase Transitions by Strain and Electric Field in Zigzag MoS2 Nanoribbons Liangzhi Kou Effective modulation of physical properties via external control may open various potential nanoelectronic applications of single-layer MoS2 nanoribbons (MoS2NRs). We show by first-principles calculations that the magnetic and electronic properties of zigzag MoS2NRs exhibit sensitive response to applied strain and electric field. Tensile strain in the zigzag direction produces reversible modulation of magnetic moments and electronic phase transitions among metallic, half-metallic, and semiconducting states, which stem from the energy-level shifts induced by an internal electric polarization and the competing covalent/ionic interactions. A simultaneously applied electric field further enhances or suppresses the strain-induced modulations depending on the direction of the electric field relative to the internal polarization. These findings suggest a robust and efficient approach to modulating the properties of MoS2NRs by a combination of strain engineering and electric field tuning. [Preview Abstract] |
|
V1.00126: M\"{o}ssbauer spectroscopy investigation of lithium oxide-hematite solid solution Vasilii Bushunow, Monica Sorescu Lithium oxide-doped hematite $x$Li$_{2}$O $_{\ast}$ (1-$x)$ $\alpha $-Fe$_{2}$O$_{3}(x=$ 0.1-0.7) solid solutions were prepared via ball milling. Samples were taken at 0, 2, 4, 8, and 12 hours ball milling time (BMT). Parameters for the obtained M\"{o}ssbauer spectra were determined by least-squares fitting using NORMOS-90 software. For all initial Li$_{2}$O concentrations, partial substitution of Fe$^{3+}$ in the Li$_{2}$O lattice and vice versa was seen beginning at two hours BMT. For $x=$ 0.1, 0.3, and 0.5, spectra were fit with one or two sextets and one quadrupole-split doublet. For $x=$ 0.7, all spectra were fit with a single sextet and one quadrupole-split doublet. With increased BMT, the abundance of the doublet increased, irrespective of initial Li$_{2}$O concentration. For example, the abundance of the doublet increased from 2.3{\%} at 2 h BMT to 11.1{\%} at 12 h BMT for $x=$ 0.1. The increasing abundance of the doublet indicates greater substitution of Li$^{+}$ by Fe$^{3+}$ in the Li$_{2}$O lattice. Increasing the initial concentration of Li$_{2}$O for constant BMT did not consistently increase the abundance of the doublet. The results of this experiment demonstrate the feasibility of forming solid solutions by purely mechanical methods, e.g. ball milling. [Preview Abstract] |
|
V1.00127: ABSTRACT WITHDRAWN |
|
V1.00128: Interplay between intrinsic and stacking-fault magnetic domains in bi-layered manganites M.A. Hossain, Mark H. Burkhardt, S. Sarkar, H. Ohldag, Y.-D. Chuang, A. Scholl, A.T. Young, A. Doran, D.S. Dessau, H. Zheng, J.F. Mitchell, H.A. D\"urr, J. St\"ohr We present a low temperature x-ray photoemission electron microscopy study of the bi-layered manganite compound La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ (BL-LSMO) to investigate the influence of stacking faults, which are structurally and magnetically different from the bi-layered host [1]. In BL-LSMO, small magnetic moment persists to $T^* = 300$ K, well above the Curie temperature of 120 K ($T_C$). Our magnetic images show that 3D stacking faults are responsible for the $T^*$ transition. Furthermore, close to $T_C$, stacking faults are well coupled to the bi-layered host with latter magnetic domains controlling the spin direction of the stacking faults. Contrary to recent reports, we find that stacking faults do not seed magnetic domains in the host via an exchange spring mechanism and the intrinsic $T_C$ of the BL-LSMO is not lower than 120 K. [1] Appl. Phys. Lett. 101, 132402 (2012) [Preview Abstract] |
|
V1.00129: Structural, AFM, MFM and magnetic studies of LaMnO$_3$ thin films prepared by atomic layer deposition method Mukesh Chandra, Himani Khanduri, S. Vasala, S. Leinberg, R. Lohmus, J. Krustok, Maarit Karppinen, Raivo Stern Structural, microstructural and magnetic properties of the thin films of LaMnO$_3$ have been investigated and will be presented in this paper. Thin films were deposited by atomic layer deposition method on silicon (100) substrates. Effect of varying thickness, annealing atmosphere and temperature has been studied on LaMnO$_3$ thin film. Films annealed in a temperature range 700-800 $^{\circ}$C show single phase perovskite crystal structure, which was confirmed from the X-ray diffraction and Raman spectra. SEM/AFM studies show uniform and high quality films with grains mostly in 20-100 nm depending on preparation conditions. MFM images measured at 65K, show different magnetic domains in films annealed in N$_2$ and O$_2$ environments. Stoichiometry, microstructure and magnetic properties are strongly dependent on films annealed in N$_2$ and O$_2$ environments; however there was no change in crystal structure. Curie transition temperature in these LMO thin films annealed in N$_2$ were found to be around 200K, while for the films annealed in O$_2$ atmosphere was around 250K. Enhanced Curie temperatures from ideal value ($\sim$140 K) can be related to non-stoichiometry in our LMO films. [Preview Abstract] |
|
V1.00130: The colossal magnetoresistance response of EuO$_{\mathrm{1-x}}$ thin films L. Hellwig, C. Beckner, M. Eblen-Zayas Phase inhomogeneity is one of the fundamental features of CMR physics in the perovskite manganites. In addition to direct imaging of phase inhomogeneity, indirect manifestations of phase inhomogeneity in the manganites include slow dynamics and persistent memory of low magnetic fields. We are investigating whether phase inhomogeneity is also a relevant model for thin films of europium-rich europium oxide (EuO$_{\mathrm{1-x}})$. EuO$_{\mathrm{1-x}}$ thin films display typical CMR behavior, including a semiconductor to metal transition associated with the onset of ferromagnetism. We have fabricated CMR EuO$_{\mathrm{1-x}}$ films by deposition of metallic Eu on fused silica substrates and subsequent oxidation of these Eu films. However, initial characterization of the EuO$_{\mathrm{1-x}}$ films indicate that these samples do not show the indirect evidence of phase-inhomogeneous behavior that is typical of CMR manganite films. [Preview Abstract] |
|
V1.00131: An In Situ Electric Field Study of Magnetoelectric Coupling in PZT-LSMO Thin Film Heterostructures Using Polarized Neutron Reflectometry and Transmission Electron Microscopy Steven Spurgeon, Jennifer Sloppy, Esther Huang, Rama Vasudevan, Samuel Lofland, Valeria Lauter, Nagarajan Valanoor, Mitra Taheri The development of ``spintronics'' devices based on charge and spin transport has signaled a paradigm shift in the design of data storage and computing technologies. Magnetoelectric materials, which exhibit intrinsic coupling between electronic and magnetic order, are ideal for these applications. Unfortunately, single-phase magnetoelectrics are exceedingly rare in nature and attention has turned to composite heterostructures that display coupled functionalities at interfaces. A promising system in which to explore this coupling is a thin film oxide heterostructure of the piezoelectric Pb(Zr0.2Ti0.8)O3 (PZT) and the half-metal La0.7Sr0.3MnO3 (LSMO). We show that it is possible to construct a capacitor-type device structure from these materials that may form the basis for an electrically-switched magnetic memory. We conduct polarized neutron reflectometry (PNR) measurements and measure changes in the magnetization depth profile throughout the composite under the reversal of an in situ electric field. We then correlate these PNR results to local strain and chemistry using transmission electron microscopy (TEM). We find that a combination of charge doping and strain mechanisms governs coupling in this system. [Preview Abstract] |
|
V1.00132: Antiferromagnetic phase in ultrathin La2/3Sr1/3MnO3 films probed by exchange bias effect Yujun Shi, Di Wu Understanding the magnetic and electronic properties of the interfaces between two different perovskite oxides has gained significant attention in recent years. An important case is the interface between manganite La2/3Sr1/3MnO3 (LSMO) and SrTiO3 (STO). Grown on STO, ultrathin LSMO acts as a ?dead layer? with strongly depressed magnetization and insulating properties below a critical thickness. Since the electronic and magnetic properties of the interfaces between two oxides are sensitive to epitaxial strain, chemical stoichiometry, and polarity discontinuity, the magnetic state of LSMO dead layer is still not well understood. Here we utilize the exchange bias (EB) effect, which generally occurred in the FM/AFM bilayers. We deposited a very thin layer of Co on ultrathin LSMO films epitaxially grown on STO(001) substrates. We observed strong EB effects and coercivity enhancement for LSMO thicknesses below 3 unit cells (u.c.). The observed effects reveal the presence of AFM phase in ultrathin LSMO. The EB effect rapidly disappears with increasing temperature. Furthermore, the observation of EB down to one u.c. LSMO demonstrates the C-type AFM ordering structure other than A-type. The EB provides an easy way to study the magnetic states of ultrathin oxide films. [Preview Abstract] |
|
V1.00133: Magnetic tunnel junction based on Mn$_{\mathrm{2-x}}$Co$_{\mathrm{2x}}$Ni$_{\mathrm{1-x}}$O$_{4}$ Mixed valent manganite spinels Jing Wu, Zhiming Huang, Junhao Chu Mn$_{\mathrm{2-x}}$Co$_{\mathrm{2x}}$Ni$_{\mathrm{1-x}}$O$_{4}$ (0$\le $x$\le $1) (MCNO), developing basically from the prototype of Mn$_{3}$O$_{\mathrm{4}}$, which are spinel-structure mixed-valent manganites and electrical and magnetic properties are closely linked with interactions among spin, orbit and lattice. The electrical conduction mechanism in MCNO is small polarons hopping between localized Mn3$+$ and Mn4$+$ octahedral sites. As we known, the magnetic orders of spinel-structure transition metal oxide are commonly ferrimagnetic with antiferromagnetic exchange between tetrahedral and octahedral sites. The conductive electron i.e. e$_{\mathrm{g}}$ orbital electron hopping between octahedral Mn$^{3+}$ and Mn$^{4+}$ sites tends to be totally spin polarized due to the strong ferromagnetic couple between octahedral sites. Vice versa, the hopping electron enhanced the ferromagnetic couple between Mn$^{3+}$ and Mn$^{4+}$ sites by RKKY indirect exchange interaction. This feature of MCNO is very potential for developing MTJ due to the totally spin polarized conductive electrons. MTJs based on MCNO have been constructed by Magnetron Sputtering method. The performance of these MTJs is under studying at present. [Preview Abstract] |
|
V1.00134: Current-induced domain wall motion in the presence of spin Hall effect Jisu Ryu, Kyung-Jin Lee, Hyun-Woo Lee Recently, traces of the spin Hall effect-induced spin transfer torque (SHE-STT) on a domain wall motion (DWM) are observed.[1] While the magnetization reversal of a single domain by SHE-STT [2] can be understood rather intuitively, SHE-STT effect on a DWM is indistinct. This issue is theoretically investigated [3] in ideal nanowires, where extrinsic pinning centers are absent. In practical situations, however, the DWM can be largely affected by the pinning centers such as nanowire defects. Here, we theoretically study SHE-STT effects on a DWM in the presence of extrinsic pinning centers. We first calculate the threshold current density $J_C$, above which a DW can escape from a pinning center. We found that SHE-STT can significantly reduce $J_C$ of a DW with certain chirality. Secondly we examine a DWM direction. In ideal nanowires [2] SHE-STT can induce a DWM against electron flow in a certain current density range. We found that this reversed DWM can be prohibited for the pinning strength larger than certain threshold value. From this feature, we suggest one way to distinguish SHE-STT and the Rashba spin-orbit coupling induced STT. [1] P. P. J. Haazen et al., arXiv:1209.232(2012). [2] Liu et al., Science 336, 555(2012). [3] S.-M. Seo et al., Appl. Phys. Lett. 101, 022405(2012). [Preview Abstract] |
|
V1.00135: Spectral and transport properties of ballistic quantum wire exposed to two magnetic spikes Bernd Schueler, Mihai Cerchez, Hengyi Xu, Thomas Heinzel Quantum Dots (QD) in two-dimensional electron gases are typically defined by nanopatterned gate electrodes.\footnote{see, e.g., L. P. Kouwenhoven et al., in Mesoscopic Electron Transport, Series E: Applied Sciences (Eds. L. L. Sohn, L. P. Kouwenhoven and G. Schon (Kluwer, 1997).} While magnetically confined QDs have been proposed theoretically to show some specific phenomena,\footnote{S.J. Lee et al., Phys. Rep. \textbf{394}, 1 (2004)} their experimental implementation is still at an early stage.\footnote{A. Tarasov et al., Phys. Rev. Lett. \textbf{104}, 186801 (2010)} We have designed a ferromagnet/semiconductor hybrid structure device which allows us to form a QD by combining electrostatic potentials with localized magnetic fields in the form of two magnetic spikes at sub-micron distances. While numerical simulations of this system predict Coulomb blockade in the closed regime and Fano type resonances in the open system,\footnote{H. Xu et al. Phys. Rev. B \textbf{84}, 035319 (2011)} we observe experimentally transmission resonances in the open system which can be interpreted as signatures of zero-dimensional states weakly bound by the magnetic field profile. [Preview Abstract] |
|
V1.00136: Magnetic properties and spin transport in hybrid boron-nitrogen-carbon nanoribbons with transitional metal impurities George Alexandru Nemnes, Tudor Luca Mitran, Adela Nicolaev, Camelia Visan, Lucian Ion, Stefan Antohe We investigate the spin filtering effects in graphene nanoribbons, where inclusions of hexagonal boron nitride were introduced together with substitutional transitional metal impurities. It was established recently [1] that boron nitride sheets with substitutional manganese impurities can be a strong candidate for future low dimensional diluted magnetic semiconductors. Our first principle approach based on non-equilibrium Green's functions gives the polarization of the spin current for different structures and biases [2]. Several spin configurations of the magnetic impurities are considered, revealing different behaviors in the spin resolved current. Some key aspects regarding spin switching effects, i.e. the turning on and off the net spin current at different biases, are also discussed. The experimental availability of the building blocks -- hybrid boron-nitrogen-carbon (BNC) materials -- as well as the magnitudes of the obtained spin current polarizations indicates a strong potential of the analyzed structures for future spintronic devices. [1] T.L. Mitran, Adela Nicolaev, G.A. Nemnes, L. Ion, S. Antohe, J. Phys.: Condens. Matter 24, 326003 (2012) [2] G.A. Nemnes, Journal of Nanomaterials, 748639 (2012); doi:10.1155/2012/748639 [Preview Abstract] |
|
V1.00137: Quantum oscillation due to Landau subbands in bulk Ge at room temperature Yuhsuke Yasutake, Susumu Fukatsu An electronic system evolves into Landau levels in strong magnetic field at low temperature unless scattering occurs. Here we attempt to observe Landau subbands at room temperature in bulk Ge. Circularly polarized photoluminescence was taken in magnetic fields up to 10 T. Quantum oscillation due to several inter-Landau level transitions in the direct valleys of Ge was clearly observed at 300 K. Individual Landau subbands are resolved as discrete peaks. The n = 0 subband showed diamagnetic shifts without optically orientation. Spin relaxation at room temperature is much faster than energy relaxation including intervalley electron-phonon scattering. Interestingly, peak separations smaller than the thermal energy were even observable, which defies the established criterion that Landau levels should develop. [Preview Abstract] |
|
V1.00138: Bilinear-biquadratic anisotropic Heisenberg model on a triangular lattice Antonio Pires Motivated by the fact that the study of disordered phases at zero temperature is of great interest, I study the spin-one quantum Heisenberg antiferromagent with a next-nearest neighbor interaction on a triangular lattice with bilinear and biquadratic exchange interaction and a single ion anisotropy using a SU(3) Schwinger boson mean field theory.I calculate the critical properties, at zero temperature, in the disordered phase. This is, for values of the single ion anisotropy paramenter D aboce a critical value Dc where a quantum phase transition takes place to a lower D phase. [Preview Abstract] |
|
V1.00139: Multiferroic properties in the spin-frustrated Cu$_2$Te$_2$O$_5$X$_2$ (X $=$ Cl and Br) Yu-Kuan Yang, Chin-Chia Yeh, Yi-Bin Jin, Sudip Mukherjee, Helmuth Berger, Hung-Duen Yang The geometrically frustrated spin-tetrahedral systems Cu$_{2}$Te$_{2}$O$_{5}$X$_{2}$ (X $=$ Cl and Br) have been studied using magnetization, dielectric constant and temperature-dependent x-ray diffraction. It was found that a antiferromagnetic ordering and a step-jump in polarization are observed at T$=$18.5 K for X$=$Cl and T$=$11.5 K for X$=$Br, respectively. The multiferroic properties for Cu$_{2}$Te$_{2}$O$_{5}$X$_{2}$(X $=$ Cl and Br) are discussed. [Preview Abstract] |
|
V1.00140: Metal doping effects on the skyrmion Cu$_2$OSeO$_3$ Da-Ye Chen, Kuo-Feng Tseng, Chih-Chieh Chou, Sudip Mukherjee, Jim-Long Her, Helmuth Berger, Hung-Duen Yang There is a considerable research interest in skyrmion whose magnetic properties have a remarkable characteristic as a vortex-like spin orientation. Recently, neutron scattering and Lorentz transmission electron miscropy measurements showed that Cu$_{2}$OSeO$_{3}$ exists a skyrmion state. We have doped transition metals (Fe, Mn, V) in Cu$_{2}$OSeO$_{3}$ and measured dc magnetization and ac susceptibility by scaning magnetic field. The Fe and Mn doping effect on the A phase in T-H phase diagrams of Cu$_{2}$OSeO$_{3}$ has been studied. Interestingly, the doping with V is different from that with Fe and Mn. The physical significance for metal doping on the skyrmion Cu$_{2}$OSeO$_{3}$ will be discussed. [Preview Abstract] |
|
V1.00141: The Effects of Magnetic Dilution on Geometrically Frustrated Germanium Based Spinels Jory Korobanik, Fereidoon Razavi Geometrically frustrated materials are characterized by the inability to simultaneously minimize exchange energy contributions. This causes a reduction of Neel ordering temperature. My research focuses on how magnetic dilution changes the physical properties of geometrically frustrated spinels. Magnetic and dielectric properties will be presented. [Preview Abstract] |
|
V1.00142: Spin glass behavior in the weberite related structure Dy$_{\mathrm{3-x}}$Y$_{\mathrm{x}}$TaO$_{7}$ Jose Francisco Gomez Garcia, Gustavo Tavizon, Alejandro Duran, Roberto Escudero Crystalline structures with tetrahedral arrangement of magnetic cations are susceptible to present non-collinear magnetism. Dy$_{3}$TaO$_{7}$ with weberite-type crystal structure has this arrangement and could display non-conventional magnetic coupling. Previous magnetic studies on Dy$_{3}$TaO$_{7}$ have characterized this as an antiferromagnetic system with T$_{\mathrm{N}}$ of about 3 K. In this work magnetic properties of polycrystalline samples of the Dy$_{\mathrm{3-x}}$Y$_{\mathrm{x}}$TaO$_{7}$, with weberite structure are presented. X-Ray diffraction of our samples are single phase in all range of compositions. Magnetic properties measured from 2 - 300 K shown a typical Curie-Weiss behavior with the Dy$^{3+}$ effective magnetic moment about 10.35 $\mu_{\mathrm{B}}$. The compositions x$=$0.66, 0.33, and 0.0 display a maximum in the susceptibility \textit{vs.} temperature at 2.3, 2.7, and 3 K respectively. This behavior has been previously assigned to an antiferromagnetic transition; however our AC magnetic measurements as a function of frequency indicate a spin glass behavior. Since magnetic cations have tetrahedral arrangement for x$=$0, a magnetic frustrated state is anticipated for this composition. [Preview Abstract] |
|
V1.00143: Critical properties of the Kitaev-Heisenberg Model Yuriy Sizyuk, Craig Price, Natalia Perkins Collective behavior of local moments in Mott insulators in the presence of strong spin-orbit coupling is one of the most interesting questions in modern condensed matter physics. Here we study the finite temperature properties of the Kitaev-Heisenberg model which describe the interactions between the pseudospin $J= 1/2$ iridium moments on the honeycomb lattice. This model was suggested as a possible model to explain low-energy physics of AIr$_2$O$_3$ compounds. In our study we show that the Kitaev-Heisenberg model may be mapped into the six state clock model with an intermediate power-law phase at finite temperatures. In the framework of the Ginsburg-Landau theory, we provide an analysis of the critical properties of the finite-temperature ordering transitions. [Preview Abstract] |
|
V1.00144: Dynamical Band-Engineering of Spin-Polarized Edge States in Nanostructures Binhe Wu The ability to engineer the band structure and electronic properties of nanostructures is a key step for potential applications ranging from spintronic devices to quantum information. We present theoretical results on the electronic and transport properties of a normal insulator, in form of a zigzag ribbon based on the graphene-like Kane-Mele model subjected to circularly polarized radiation. It is found that chiral edge-states can be induced in the band gap of the quasi-energy spectra under periodic driving. More interestingly, for appropriate parameters, there exists a single chiral edge state at each boundary of the sample. As a result, the conductance shows plateau structure with the step height e$^{2}$/h as we increase the ac field intensity. These observations may find their potential applications for high-efficiency non-magnetic spin injection which can be readily tuned by modulating an external ac field. \\[4pt] [1] B. H. Wu, Q. Liu, X.-Y. Jiang, and J. C. Cao, Appl. Phys. Lett. 100, 203106 (2012). [Preview Abstract] |
|
V1.00145: Tailoring spin injection and magnetoresistance in ferromagnet/graphene junctions from first principles Predrag Lazic, Guilherme Sipahi, Roland Kawakami, Igor Zutic Recent experimental advances in graphene [1-3] suggest intriguing opportunities for novel spintronic applications which could significantly exceed the state-of-the art performance of their conventional charge-based counterparts[4,5]. However, for reliable operation of such spintronic devices it is important to achieve an efficient spin injection and large magnetoresistive effects. We use the first principles calculations to guide the choice of a ferromagnetic region and its relative orientation to optimize the desired effects. We propose structures which could enable uniform spin injection, one of the key factors in implementing scalable spintronic circuits. [1] C. Josza and B. J. van Wees, Graphene Spintronics, in Handbook of Spin Transport and Magnetism, edited by E. Y. Tsymbal and I. Zutic (CRC Press, New York, 2011). [2] W. Han et al., Phys. Rev. Lett. {\bf 102}, 137205 (2009). [3] W. Han, K. Pi, K. M. McCreary, Y. Li, Jared J. I. Wong, A. G. Swartz, and R. K. Kawakami, Phys. Rev. Lett. {\bf 105}, 167202 (2011). [4] H. Dery, H. Wu, B. Ciftcioglu, M. Huang, Y. Song, R. Kawakami, J. Shi, I. Krivorotov, I. Zutic, and Lu J. Sham, IEEE Trans. Electron Devices 59, 259 (2012). [5] H. Dery et al., Proc. of SPIE {\bf 8100}, 81000W (2011) [Preview Abstract] |
|
V1.00146: Macroscopic quantum effects in a rotating nanomagnet Gwang-Hee Kim We study spin tunneling in a rotational magnetic nanoparticle in the presence of sound waves. Equations of motions are derived that couple spin and mechanical degrees of freedom and the perturbative solution of these equations is obtained. We find quantum beats of magnetization which are strongly affected by the moment of inertia of the molecular magnet and its total angular momentum. The optimal condition for generating the quantum beat of magnetization with a large period is discussed. [Preview Abstract] |
|
V1.00147: High-field NMR spectroscopy of the iron based superconductor LiFeAs Hannes Kuehne, A.P. Reyes, P.L. Kuhns, M.J.R. Hoch, S. Yuan, H.-J. Grafe, S. Aswartham, S. Wurmehl, B. Buechner The stoichiometric compound LiFeAs is unique among the iron based superconductors. It exhibits superconductivity below 18 K without the usually necessary introduction of chemical doping. From a number of macroscopic experiments, upper critical fields of 26 T or higher for a magnetic field orientation parallel to the FeAs planes were reported. But, until now, no local probe techniques were applied for the characterization of the microscopic electronic properties in this high-field parameter regime. On our poster, we present the results of recently performed high-field (up to 30 T) NMR experiments on three high quality LiFeAs single crystals, suggesting an upper critical field much lower than 26 T. We discuss the implications of the observed, field-induced suppression of the superconducting gap in this compound and its manifestation in the temperature dependent Knight shift, nuclear spin-lattice and spin-spin relaxation rates for fields and temperatures in the normal and superconducting state. [Preview Abstract] |
|
V1.00148: SUPERCONDUCTIVITY |
|
V1.00149: Bromine-doping dependence of crystal structure and superconductivity in FeSe$_{1-x}$Br$_{x}$ Y.T. Shen, S.C. Chen, K.J. Syu, W.H. Lee Our experimental data indicate that the crystal structure formation in FeSe$_{1-x}$Br$_{x}$ is dependent on the amount of Br. For the samples with $x$ between 0.18 and 0.3, the single tetragonal $\beta $-FeSe phase with space group P4/nmm could be obtained by carrying out the low-temperature (400 $^{\mathrm{o}}$C) annealing after reaction at 680 $^{\mathrm{o}}$C. As to the sample with $x=$ 0.1, a heat firing at 680 $^{\mathrm{o}}$C is in favor of forming single hexagonal $\delta $-FeSe phase with space group P6$_{3}$/mmc. Powder x-ray diffraction and crystallographic data provide the suggestion that the $\beta $ tetragonal PbO-type phase is related to the superconducting state while the $\delta $ hexagonal NiAs-type phase has no effect on the superconductivity. Magnetization data confirm the bulk character of the superconducting state with a T$_{c}$ around 5 K. Larger superconducting volume fraction appears in the single-phase sample with $x$ near 0.2. [Preview Abstract] |
|
V1.00150: Optical investigation of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ detwinned by tunable uniaxial applied pressure Chiara Mirri, Adam Dusza, Sandra Bastelberger, Andrea Lucarelli, Hsueh-Hui Kuo, Jiun-Haw Chu, Ian Fischer, Leonardo Degiorgi The iron-pnictide superconductors are excellent materials where one can study the competition between structural, magnetic and superconducting phases. In the parent compound (i.e. x = 0\%) and in the so called underdoped regime (x$<$6\%) an antiferromagnetic transition occurs at T$_N$ with an almost coincident tetragonal-to-orthorhombic structural distortion at T$_s$ $\geq$ T$_N$. The in-plane anisotropy of the orthorombic phase was found to be masked by the formation of twin domains in these compounds, which can be detwinned by applying uniaxial pressure. Here we report on an optical investigation performed with electromagnetic radiation polarized along the a and b axes of Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals , for x=0, 2.5\% and 4.5\%, detwinned by in-situ tunable uniaxial pressure applied across the stuctural and the magnetic transitions. We show in details the experimental setup, i. e. the pressure device used to detwin the samples, and the most remarkable results. In particular we focus on the evolution of the anisotropy in the reflectivity by applying and releasing pressure at different fixed temperatures. [Preview Abstract] |
|
V1.00151: Magnetic Properties of Iron Chalcogenide Superconducting Materials for Energy Storage Applications Destenie Knock, Korey Pough, Abebe Kebede, Dereje Seifu A superconductor is characterized by its ability to conduct electricity without loss and expel magnetic flux when exposed to an external magnetic field. Additionally, the smaller the relaxation rate ($S=$dM/dt), the better the material for energy storage. This research focuses on the recently discovered high-quality, single-crystalline Iron-based superconductors of FeTe$_{\mathrm{1-x}}$Se$_{\mathrm{x}}$ (x $=$0.5), with a transition temperature at $T_{c}=$14.5K. Standard creep models are used to analyze the data and determine the effective pinning potential. The magnetization relaxation were measured the Superconducting Quantum Interference Device (SQUID). The relaxation~rate~appears to be independent of field and temperature for fields below 3T and temperatures below 7K. This result shows that the thermally activated flux motion is not as significant as in other high temperature superconductors, hence FeTe$_{\mathrm{1-x}}$Se$_{\mathrm{x}}$, can be a candidate for wire development to be used in Superconducting Magnetic Energy Storage systems. [Preview Abstract] |
|
V1.00152: Crystal structure and physical properties in Fe-Te-Br C.H. Ho, S.C. Chen, K.J. Syu, W.H. Lee Within a spin fluctuation driven scenario of superconductivity the results indicate that FeTe with doping is a likely higher-temperature superconductor. However, Fe$_{1+x}$Te forms the same tetragonal structure with 0.06 \textless y \textless 0.17. The excess Fe (2) not only stabilizes the PbO-type crystal structure with space group P4/nmm but also is strongly magnetic as an electron donor while the deficit of Fe in Fe$_{1-x}$Te will result in the hexagonal structure with space group P6$_{\mathrm{3}}$/mmc. In this work, five single tetragonal phase samples with space group P4/nmm and three single hexagonal phase samples with space group P6$_{\mathrm{3}}$/mmc have been made in Fe-Te-Br. Magnetic and electrical properties as well as the possibility of high-T$_{c}$ superconductivity in the Fe-Te-Br system investigated will be discussed. [Preview Abstract] |
|
V1.00153: Thermopower as sensitive probe of electronic nematicity in iron pnictides Philipp Gegenwart We study the in-plane anisotropy of the thermoelectric power and electrical resistivity on detwinned single crystals of isovalent substituted EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_2$. Compared to the resistivity anisotropy the thermopower anisotropy is more pronounced and clearly visible already at temperatures much above the structural and magnetic phase transitions. Most remarkably, the thermopower anisotropy changes sign below the structural transition. This is associated with the interplay of two contributions due to anisotropic scattering and orbital polarization, which dominate at high- and low-temperatures, respectively. Preprint available at arXiv:1210.2634. [Preview Abstract] |
|
V1.00154: Effects of pressure on T$_{c}$ in (Tl$_{0.59}$Cs$_{0.26})$Fe$_{1.9}$Se$_{2}$ S.C. Chen, K.J. Syu, H.H. Sung, W.H. Lee, C.C. Li, Y.Y. Chen Hydrostatic-pressure (up to 0.96 GPa) dependence of T$_{c}$ in a newly discovered Fe-based superconductor (Tl$_{0.59}$Cs$_{0.26})$Fe$_{1.9}$Se$_{2}$ is reported. The room temperature powder $x$-ray diffraction and crystallographic data provide the evidence for bulk superconductivity with T$_{c}$ around 28 K in a tetragonal ThCr$_{2}$Si$_{2}$-type structure at ambient pressure. Static Magnetization measurements under pressure indicate that the linear increase in T$_{c}$ is initially rapid (dT$_{c}$/dP $=$ 9.9 K GPa$^{-1})$ but slows down to dT$_{c}$/dP $=$ 2.5 K GPa$^{-1}$ for P \textgreater 0.18 GPa. The T$_{c}$ of the superconducting phase is 32 K at pressure P $=$ 0.96 GPa. The simple rigid band model may not be sufficient to account for the observations if the lattice parameters of the unit cell are linearly decreased with the hydrostatic pressure. [Preview Abstract] |
|
V1.00155: Conventional and Time-Resolved Infrared Spectroscopy of La-1111 Thin Films Xiaoxiang Xi, Y. M. Dai, C. C. Homes, M. Kidszun, S. Haindl, G. L. Carr We have performed both conventional as well as time-resolved far-infrared spectroscopy on LaFeAsO$_{1-x}$F$_x$ pnictide thin films. The conventional spectroscopy results can be fit using a simple gapped superconductor + normal conductor two-component model. Absorption by quasiparticles in a gap system with nodes is a plausible explanation for the normal component [Lobo \textit{et al}. Phys. Rev. B 82, 100506(R) (2010)]. The time-resolved study is performed by laser-pump, far-IR probe spectroscopy using synchrotron radiation at NSLS beamline U4IR. A laser pulse breaks superconducting pairs and the synchrotron probe is used to sense the recombination process. In contrast to the picosecond response observed for cuprate superconductors, we observe a nanosecond response typical of a fully gapped superconductor where phonon-bottleneck effects slow the effective recombination rate. This result suggests the presence of a full isotropic gap, as might exist at lower energies due to electronic scattering [Carbotte \textit{et al}. Phys. Rev. B 81, 104510 (2010)]. [Preview Abstract] |
|
V1.00156: Low Field Microwave Absorption in thin films of FeSe and FeTeSe deposited by PLD Jonathan Yuen, Austin Howard, Li Chen, Haiyan Wang, Myron Salamon, Anvar Zakhidov Our motivation is to study the 2D superconductivity of Fe-based materials deposited on different substrates - glass, STO and CNT. Pulsed laser deposition of FeSe and FeSe0.5Te0.5 films was performed. Deposition conditions including laser fluences, frequency, temperature and back pressure were optimized for different substrates. When anisotropic superconductors are confined to lower dimensions, interesting effects have been observed. Enhanced superconductivity might occur from interfacial effects, and it has been claimed that an atomic layer of FeSe may exhibit higher Tc at STO interface. LFMA (microwave absorption at low magnetic fields) is a highly sensitive tool for searching for possible higher Tc phases in FeSe based films, especially when combined with ESR, SQUID magnetometry and resistivity measurements. LFMA uses an external magnetic field to create Josephson Junction vortices, which are non-resonantly excited by MW radiation. Such vortices have strong angle dependence in 2D systems and can be used to carefully probe and understand confinement effects. The LFMA spectrum exhibits two distinct features in different temperatures: a hysteretic LFMA below 8K and non-hysteretic narrow LFMA at higher T. Angle dependences of the LFMA signals are analyzed and the origin of the higher Tc LFMA signals will be discussed. [Preview Abstract] |
|
V1.00157: Bulk superconductivity in novel Bi$_4$O$_4$S$_3$ compound Shiva Kumar Singh, M. Husain, S. Patnaik, V. P. S. Awana We report here synthesis and superconductivity in BiS$_2$ based newly discovered Bi$_4$O$_4$S$_3$ compound. The compound is synthesized through vacuum encapsulation technique and is contaminated with small impurities of Bi$_2$S$_3$ and Bi. The compound is crystallized in tetragonal I4/mmm space group. Bulk superconductivity with superconducting transition temperature (T$_C$) of 4.4 K is confirmed by AC, DC magnetization and resistivity measurements. For further confirmation of intrinsic bulk superconductivity, we have heat treated Bi at same temperature and in similar condition. Bi is crystallized in rhombohedral R-3m space group (impurity phase Bi is also indexed in same space group) and is non-superconducting. This excludes any possibility of impurity driven superconductivity in the Bi$_4$O$_4$S$_3$ compound. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The magneto-transport $\rho{(T, H)}$ measurements showed a resistive broadening and decrease in T$_C$ ($\rho = 0$) to lower temperatures with increasing magnetic field. The extrapolated upper critical field H$_{c2}$(0) is around 31 kOe. In the normal state the $\rho$ $\sim$ T$^2$ is not indicated. [Preview Abstract] |
|
V1.00158: Magnetic property and phase diagram of single-crystalline over-doped Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Fe$_2$As$_2$ Yu Li, Chenglin Zhang, Pengcheng Dai Sizable single-crystalline samples of hole-doped Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Fe$_2$As$_2$ with x \textgreater\ 0.4 have been grown and characterized via magnetic measurements. Tc of our samples decreases from that of optimal doping as doping rate of K increases. Sharp transitions in M(T) curves indicate high quality of our sizable crystals which has never succeeded in over-doped region due to extreme nonhomogeneous property of this kind of material. With increasing K content, electron Fermi surface diminishing and nesting between hole FS and electron FS disappearing consequently, it is predicted that there exists a transition from s-wave superconducting state to d-wave yet without sufficient experimental evidences. Our results made it possible to further study on the hole-overdoped Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Fe$_2$As$_2$ series and provide a significant platform to test and verify these current theories and understand the underlying pairing mechanism in iron-based superconductors. [Preview Abstract] |
|
V1.00159: Investigation of Gd effect on $YBa_2Cu_3O_{7-\delta}$ superconducting compounds Nevin Soylu, Osman Gorur, Ahmet Varilci, Cabir Terzioglu We studied the change of pinning mechanism, electrical, structural, physical, and superconducting properties of $YBa_2Cu_{3-x}Gd_xO{7-\delta}$ superconductor samples prepared by the conventional solid state reaction method ($x=0, 0.025, 0.050, 0.100$ and $0.150$) by use of dc resistivity, X-ray analysis (XRD),and scanning electron microscopy (SEM). The obtained results demonstrate that T$_{c,offset}$ values of the samples decrease slowly with the increase in the Gd content. The maximum T$_{c,offset}$ (92.0 K) is obtained for the pure sample prepared at 940$^\circ$ C for 20 h in air atmosphere while the minimum value of 83.3 K is found for the sample doped with 0.150 Gd content. Moreover, it is obtained that J$_c$ values reduce from 132 to 34 A/cm$^2$ with the enhancement of the Gd level in the crystalline structure. The peak intensities belonging to Y123 (major) phase are obtained to decrease whereas the peak intensities of the minor phases such as BaCuO$_2$ and Y211 are found to enhance systematically with the increment in the Gd content in the system, illustrating that partial substitution of Cu$^2+$ions by Gd$^3+$ ions are carried out successfully. [Preview Abstract] |
|
V1.00160: ABSTRACT WITHDRAWN |
|
V1.00161: Study of solitons in strongly correlated systems Irina Bariakhtar, Alexander Nazarenko The aim of this paper is to draw the researchers' attention to the fact that the study of the scattering of x rays (or, incidentally, the scattering of light or electrons), together with an investigation of the neutron scattering, can give important experimental information about the properties of the solitons in solids. In this work we discuss the one-dimensional solitons that arise in two-dimensional (quasi-two-dimensional) crystals. As an example of such systems we use some high-temperature superconductor materials. In this paper we calculate the structure factors of solitons. We consider examples of solitons corresponding to the formation of a kink (fold) in a system of adatoms on the surface of a substrate. We discuss that by calculating the cross section for elastic scattering of x-rays and comparing it to experimental data one can investigate the presence and properties of solitons in such systems. [Preview Abstract] |
|
V1.00162: Flux Quantization Without Cooper Pairs Alan M. Kadin It is universally accepted that the superconducting flux quantum h/2e requires the existence of a phase-coherent macroscopic wave function of Cooper pairs, each with charge 2e. On the contrary, we assert that flux quantization can be better understood in terms of single-electron quantum states, localized on the scale of the coherence length and organized into a real-space phase-antiphase structure [1]. This packing configuration is consistent with the Pauli exclusion principle for single-electron states, maintains long-range phase coherence, and is compatible with much of the BCS formalism. This also accounts for h/2e in the Josephson effect [2], without Cooper pairs. Experimental evidence for this alternative picture may be found in deviations from h/2e in loops and devices much smaller than the coherence length. A similar phase-antiphase structure may also account for superfluids, without the need for boson condensation.\\[4pt] [1] A.M. Kadin, ``Superconductivity without Pairing?,'' http://arxiv.org/abs/0909.2901 (2009).\\[0pt] [2] A.M. Kadin, ``Josephson Junctions Without Pairing?,'' http://arxiv.org/abs/1007.5340 (2010). [Preview Abstract] |
|
V1.00163: Electronic origin of charge-density wave instability in underdoped YBCO Riccardo Comin, G. Levy, I. Elfimov, G.A. Sawatzky, A. Damascelli Very recent diffraction and scattering results found direct (i.e. structural) evidence for an incommensurate charge-density-wave (CDW) in underdoped YBCO ($ p \sim 0.1-0.12 $), which appears to be electronically-driven and competing with superconductivity. We have investigated the origin of this CDW-instability by analizing in detail the charge susceptibility starting from the experimentally available ARPES maps, and using an RVB-derived self-energy whose parameters are tuned to maximize comparison to ARPES data. We derive the non-interacting and full susceptibilities, which reveal how the electronic response evolves starting from the bare, uncorrelated (LDA-like) band structure to the fully dressed single-particle spectral function (incorporating both coherent and incoherent excitations). We then compare the temperature-dependent calculations to the scattering results and resolve the connection between single-particle spectroscopies and structural probes in YBCO. [Preview Abstract] |
|
V1.00164: Capillary Condensation Transitions for Various Geometries Carolina Ilie, Anastasia Yorke, Katharyn Christiana, Marie Romano 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. Other interesting cases, for example the capillary condensation between two cylinders, may be inspected. [Preview Abstract] |
|
V1.00165: High pressure Moissanite-anvil cells for the low temperature Hall effect measurements of oxide superconductors Shusuke Yomo, Stanley W. Tozer The Hall effect was successfully measured for a single crystal of high temperature superconductor in a Moissanite-anvil clamp cell up to 5 GPa, with proper arrangement of lead wires and a sample. Zylon gasket, good in electrical insulation, worked well up to 5 GPa. The 30-40 \% increase of the clamped pressure was observed during cooling to below 60 K. The appreciable pressure effect of the a-b plane Hall coefficient was observed and negative for $La_{2-x}Sr_{x}CuO_{4}$ with x = 0.090. The result is discussed with those for sintered samples and those studied with a different pressurizing method. [Preview Abstract] |
|
V1.00166: Finite temperature dynamical density matrix renormalization group study of high-energy optical conductivity in high-Tc cuprates Shigetoshi Sota, Tomonori Shirakawa, Seiji Yunoki Synchrotron-based high-energy optical conductivity measurement has been proposed as an effective experimental means to investigate the magnetic correlations around doped carriers in strongly correlated materials. For example, very recent experiments on high-Tc cuprates have observed the surprisingly significant temperature dependence of the spectra for an energy region much higher than the value of the spin exchange ($\sim$ 125 meV) below room temperature. Motivated by these experiments, we here study the high-energy optical conductivity and its temperature dependence of an effective model for high-Tc cuprates using massively parallelized dynamical density matrix renormalization group (DMRG). To describe the Zhang-Rice singlet as well as the high-energy excitations properly, we employ a one-dimensional three-band Hubbard model describing a CuO$_3$ chain. Our finite-temperature dynamical DMRG calculations find the strong temperature dependence of the optical conductivity, which occurs over a wide range of the excitation energy. We attribute this anomalously strong spectral redistribution to a magnetic origin, thus indicating that the high-energy optical conductivity contains valuable information of spin dynamics. [Preview Abstract] |
|
V1.00167: Core-level Photoemission Study for Cuprates with a Dynamical Mean-Field Approach Considering Realistic Crystal Structure Atsushi Hariki, Takayuki Uozumi Recently, remarkable experimental progress reveals some characteristic spectral features in the 2p$_{3/2}$main line of Cu 2p core-level X-ray photoemission spectra (XPS)[1]. The structures show strong material dependence and drastic changes for electron or hole doping. Van Veenendaal et al., pointed out that the main line shape is strongly affected by the so-called nonlocal screening which is accompanied by a formation of a Zhang-Rice singlet (ZRS) in the XPS final state[2]. On the other hand, Taguchi et al., shows these features are reproduced by introducing an phenomenological extended impurity model[1]. We consider that this topic on 2pXPS of cuprates still remain controversial. In this study, we propose another approach based on the dynamical mean field theory(DMFT) considering the realistic crystal structure. Many-particle effects including the ZRS is appropriately embedded in the hybridization function of a single impurity Anderson model through the DMFT self-consistent cycle. Our approach reproduces experimental results and shows that the Cu 2p$_{3/2}$ main line is closely related with the quasi-particle structure near the Fermi energy.\\[4pt] [1] M.Taguchi et al.,Phy.Rev.Lett.95(2005)177002 [2] M.A.van Veenendaal and G.A.Swatzky Phys.Rev.Let70(1993)2459 [Preview Abstract] |
|
V1.00168: Monte Carlo and Langevin dynamics simulations for the steady-state and relaxation properties of magnetic flux lines in type-II superconductors Hiba Assi, Ulrich Dobramysl, Michel Pleimling, Uwe Tauber We investigate the non-equilibrium relaxation properties and steady states of interacting magnetic flux lines in type-II superconductors in the presence of driving external currents and / or different types and configurations of pinning centers. We model the vortices as elastic lines, and study the competing effects of thermal fluctuations, mutual repulsion, and pinning to defects. We employ both three-dimensional Monte Carlo and more efficient Langevin molecular dynamics simulations. Comparison of the resulting data for the non-equilibrium stationary states as well as the preceding relaxation regimes allows us to validate the utilization of both algorithms in out-of-equilibrium settings. We furthermore carefully analyze finite-size effects. [Preview Abstract] |
|
V1.00169: Resistive Losses in Single-Crystal Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ Brendan Benapfl, Chenglin Zhang, Pengcheng Dai, H.A. Blackstead Temperature- and field-dependent surface resistance measurements were conducted using Electron Spin Resonance (ESR) techniques on single-crystal $\mathrm{Ba_{0.6}K_{0.4}Fe_{2}As_{2}}$ samples (\textit{rf} frequency = 20.3 GHz). At a fixed temperature, field scans were performed at various angles of $H_0$ with respect to $H_{rf}$. To our knowledge, this is the first report of such studies on this material. For temperatures exceeding $T_C$, there was no evidence of iron ESR. In the superconducting state, the samples exhibit dissipative losses which increase monotonically as a function of applied field for fixed temperature. The level of field-dependent dissipation increases as $T$ approaches $T_C$ from below, and vanishes at the transition. [Preview Abstract] |
|
V1.00170: Magnetic Field Effects on Relaxation Parameters of The Hexamethylenetetramine (HMT) Nurcan Dogan The use of low magnetic field is one of the method for improvement of the signal to noise ratio (SNR) of detection of the chemical compounds by nuclear quadrupole resonance (NQR). We investigated the FID phenomenon of nuclear quadrupole resonance (NQR) from hexamethylenetetramine (HMT), C$_{6}$H$_{12}$N$_{4,}$ under magnetic field. The influence of the low magnetic field (up to 30 mT) was investigated for the detection of the pulse NQR signal for HMT~ We detected the pure NQR FID signal of HMT with a short pulse interval. The intensity of the FID signal changed with applied magnetic field. The application of the low magnetic field produces the splitting and brodening of the NQR line. We observed T$_{1}$, T$_{2}$ and $T_{2}^{\ast } $. HMT has a long $T_{2}^{\ast } $(near 1.5ms). This one represents the suitable sample for investigation of the influence of low magnetic field for NQR detection. The application of the low magnetic field produces the splitting and brodening of the NQR line. [Preview Abstract] |
|
V1.00171: Polarizabilities of Halide Ions Co-Adsorbed on Silver Nanoparticles and Their Relationship to Increased Surface-Enhanced Raman Intensities of Rhodamine-6G and Pyridine Michael Cole, Paul Jagodzinski Glaspell et. al. (2004), found a linear relationship between the intensities of surface-enhanced Raman (SER) signals of selected vibrational modes of rhodamine-6G (R6G) and the polarizabilities of co-adsorbed halide ions. Furthermore, they noticed that the slopes of intensity versus time plots for R6G also exhibit a linear relationship with the halide polarizabilities. We will present similar results from the SER signals from selected vibrational modes of pyridine and the polarizabilities of co-adsorbed halide ions. In addition, we will present a plausible relationship between the adsorbates and the electric field of the induced dipole of the halide ions. [Preview Abstract] |
|
V1.00172: SQUIDs Fabrication with the Weak Links Abdelaziz Ramzi, Serge A. Charlebois We present a new technique to fabricate SQUIDs nanobridges as the weak links. We have shown that these chemical-mechanical polishing based process has minimal impact on Al and Nb superconducting properties as demonstrated on long microstructures. This process allows realizing ``2D nanobridges'' formed of the same material as the electrodes and with same thickness. The Nb nanobridges are approximately 100~nm wide and long and 20~nm thick. Similar structures have been fabricated in Ti and Al. We are working at increasing the quality of the deposited films especially in the initial phase for this is the material that remains after CMP and forms these very thin nanobridges. In these very thin structures, it is critical to have high quality material being deposited from the very start of the deposition process as it is those initial layers that are left as a device after CMP [1]. Also allows producing ``3D structures'' with nanobridges thinner (e.g. 20 nm) than the leads (e.g. 100 nm) in a single lithography step. In this case, we also show that the nanobridge can be made of a material other than the leads thus allow SS'S or SNS type of weak links.\\[4pt] [1] A. Ramzi et al., \textit{Physics Procedia,} Volume \textbf{36}, (2012), 211--216. [Preview Abstract] |
|
V1.00173: Andreev Interferometry of Proximitized Semiconductor Nanowires C. Checkley, D. Yuvaraj, H. Liu, M. Sourribes, M. Panfilova, P.A. Warburton, E.J. Romans By using the proximity effect to combine the spin orbit coupling of a semiconducting nanowire with a conventional superconductor it is possible to create a p$_{\mathrm{x}}+$ip$_{\mathrm{y}}$ superconductor capable of supporting Majorana fermions [1]. We have designed a circuit in which an Andreev Interferometer is connected via superconducting leads to a proximtized InSb nanowire to investigate the presence of Majorana fermions in the nanowire. An Andreev Interferometer is a mesoscopic device consisting of a normal metal cross. One branch of the cross is placed between two superconducting electrodes while the resistance of the other branch is monitored. Phase coherent transport causes the resistance to oscillate as a function of the phase difference between the two superconductors [2]. In this way it is possible to use the interferometer as a detector of superconducting phase. A magnetic flux perpendicular to the circuit will create an external phase. If Majorana fermions are present in the nanowire, the phase around loop is distributed differently and there is a change in the magneto-resistance oscillations of the interferometer. In this paper we explain how the presence of Majorana fermions will affect the behaviour of our junction, describe our fabrication process and discuss our preliminary results. [1] R.M. Lutchyn et al., Phys. Rev. Lett. 105, 077001 (2010). [2] V.T. Petrashov et al., Phys. Rev Lett. 95, 147001 (2005). [Preview Abstract] |
|
V1.00174: Superconducting Quantum Interference Devices incorporating an InSb-Superconductor Proximity Effect Junction Yuvaraj Dhayalan, Christoper Checkley, Huiyun Liu, Ed Romans There have been several recent proposals for devices to detect Majorana fermions at the interfaces between conventional superconductors and semiconductors with particular types of spin-orbit coupling. One very recent proposal (Wang et al., arXiv:1204.5616 [cond-mat.supr-con]) has suggested using a novel dc superconducting quantum interference device (SQUID) comprising a conventional Josephson junction in parallel with a Majorana-carrying superconductor-semiconductor (S-Sc-S) junction. We have realised such a device using a niobium nanobridge (Dayem bridge) and an InSb-based S-Sc-S junction. The S-Sc-S junction was formed by structuring an InSb film (45 nm thick) grown by Molecular Beam Epitaxy (MBE) into a nanowire (150 nm wide) by electron beam lithography and reactive ion etching. The electrical characteristics and magnetic flux response of the device were measured at low temperature. We discuss the fabrication of the device, and the evidence for the presence of Majorana fermions in the InSb nanowire, based on the observed magnetic flux response of the SQUID. [Preview Abstract] |
|
V1.00175: Mesoscopic fluctuations of the critical current in graphene-based Josephson junctions Mauricio Pilo-Pais, Ivan Borzenets, Ulas Coskun, Alex Smirnov, Gleb Finkelstein We study the critical current $I_C$ and the normal resistance $R_N$ in superconductor-graphene-superconductor (SGS) Josephson junctions. We observe large (close to 100\%) and highly reproducible fluctuations of critical current over small scale changes in $V_{\mathrm{gate}}$. Unlike fluctuations of critical current previously seen in 1D nano-wires, the fluctuations in graphene do not necessarily track the small scale changes in normal resistance. We attribute these fluctuations to the disordered nature of our wide graphene junctions, where the critical current may be dominated by a few regions, different from those regions which determine the normal resistance. [Preview Abstract] |
|
V1.00176: Multiple Andreev Reflection in LAO/STO Heterostructure Jimin Chun, Jinhee Kim Electrical transport properties of LaAlO3/SrTiO3 (LAO/STO) oxide bilayer, grown by pulsed-laser deposition, was investigated. Superconducting proximity junction with an Al electrode is fabricated. Pronounced peaks in the differential conductance curve, attributed to the Multiple Andreev Reflection (MAR), was observed. From the MAR peaks, the superconducting energy gap of the LAO/STO bilayer was estimated. Unlike the conventional superconductor, the LAO/STO bilayer showed a very small superconducting gap. Experimental results also with a normal metal Au, instead of a superconductor Al, will be presented. [Preview Abstract] |
|
V1.00177: Spin fluctuation pairing in the SDW state of electron-doped cuprates Wenya Rowe, Ilya Eremin, P. J. Hirschfeld The proximity of the antiferromagnetic state is considered to give rise to superconductivity in systems such as electron doped cuprates and iron-pnictide materials. We generalize the spin bag theory proposed by Schrieffer et al\footnote{J. R. Schrieffer, X. G. Wen, and S. C. Zhang, ``Dynamic spin fluctuations and the bag mechanism of high-$T_c$ superconductivity," Phys. Rev. B, 39, pp. 11663-11679 (1989).}, and investigate the effects on pairing of possible electron pockets and simultaneous electron and hole pockets. We also take into account the particle-hole excitations which arise from the itinerant nature of the system and the effects of next-nearest hopping. The contributions of the charge-fluctuation channel, amplitude and orientational spin-fluctuation channels to superconductivity will be discussed. [Preview Abstract] |
|
V1.00178: Vortex states in nanosuperconductor Liviu Chibotaru, Bart Deloof, Victor Moshchalkov The vortex states in nanoscale superconductors are investigated within generalized Bogolubov-de Gennes theory. For symmetric (square-shaped) samples thermodynamically stable vortex phases form symmetry-consistent patterns and no transition to conventional Abrikosov-like vortex patterns occurs till T = 0K for sizes not exceeding 25 nm. For vorticity $L = 2$ a giant vortex is stabilized at temperatures in the vicinity of T$_c$, which transforms into a giant antivortex $L = -2$ and four normal vortices with lowering the temperature. On the other hand, the vortex pattern for vorticity $L = 3$ corresponds to an antivortex $L = -1$ and four normal vortices in the whole temperature domain. [Preview Abstract] |
|
V1.00179: Noise measurements of high temperature superconductor twin boundary junctions Li Xiang, Fang Xu, Liang Liu, Jian Wei Doubled shot noise is considered as a proof of Cooper pair tunnelling through Superconductor-Normal metal junctions. For high temperature superconductor this doubling of shot noise has yet to be observed. More interestingly, in the so called pseudogap regime, observation of doubling of shot noise can provide direct evidence of preformed Cooper pairs in the normal state. As a preliminary study, we measure the noises of single and serial of twin boundary junctions and analyse their second and third order spectra (bispectrum). The separation of low frequency noise, thermal noise, and possibly shot noise is discussed in detail. [Preview Abstract] |
|
V1.00180: UV-Ozone Treatment for Improved Contacts to Graphene Wei Li, David Gundlach We report on the influence of UV-Ozone (UVO) treatment on the electrical properties of metal contacts formed to single layer graphene grown by CVD. Polycrystalline graphene was grown on copper foil and transferred onto a heavily doped silicon wafer with a 300 nm thick thermally grown SiO$_{2}$ insulator using the method described previously [1]. E-beam deposited Ti (20 nm)/Au (80 nm) contacts were patterned by photolithography and a lift-off process. Just prior to depositing the contacts, the substrates were UVO treated in a commercial system for times ranging from 5 minutes to 25 minutes, where only the graphene surface in the lithographically-defined openings of the resist layer were exposed to UVO. The devices were completed by oxygen plasma etching the graphene in the field regions. For comparison, we fabricated test structures in parallel without UVO treatment. [Preview Abstract] |
|
V1.00181: ABSTRACT WITHDRAWN |
|
V1.00182: Enhanced Tc in MgB$_2$ by SWCNT Dilution Danhao Ma, Ruwantha Jayasinha, Kofi Adu, Gamini Sumanasekera We report for the first time a nonsubstitutional hole-doping of the MgB$_{2}$ structure and an increase in Tc by SWCNT dilution. The SWCNT concentration was varied from 0.05wt{\%} to 5wt{\%}. We investigated the temperature dependence resistivity from 10K to 300K of sintered MgB$_{2}$ powder containing dilute amount of ultra-high purity single wall carbon nanotubes. Micro-Raman spectroscopy, field emission scanning electron microscope and x-ray diffraction were used to analyze the interfacial interactions between the carbon nanotubes and the magnesium diboride grains. We obtained an increase in Tc from 41.1K to 45.8K. This is attributed charge transfer: electron transfer from the MgB$_{2}$ structure to the SWCNT structure. This consequently leads to hole-doping of the MgB$_{2}$ structure and the enhancement we see in Tc. This is confirmed by micro-Raman analysis of the phonon states of the SWCNT in the composites. This is explained in terms of the interplay between impurity scattering and hole-doping. This report provides experimental alternative pathway to hole-doping of MgB$_{2}$ without appealing to elemental substitution. [Preview Abstract] |
|
V1.00183: Surface Ferromagnetism and Superconducting Properties of Nanocrystalline Niobium Nitride Shipra Rai, Nitesh Kumar, A. Sundaresan We report magnetic, transport (electrical) and thermal (heat capacity) properties of nanocrystalline $\delta $-NbNx prepared by urea-nitridation method and heated at three different temperatures, 700, 800 and 900 $^{\circ}$C respectively. Particle size and their agglomeration increases with increasing synthesis temperature. The sample prepared at 900 $^{\circ}$C, showed the highest transition temperature, Tc(onset) $=$ 16 K with a transition width ($\Delta $Tc) of 1.8 K, as obtained from resistivity measurement on the cold-pressed bar. Above Tc, magnetization measurements revealed the presence surface ferromagnetism that coexists with superconductivity below Tc. Heat capacity measurements confirm the bulk nature of superconductivity with strong electron -phonon coupling. These results are compared with those of the samples prepared at 800 $^{\circ}$C with a lower Tc (10K) and 700 $^{\circ}$C, which is non-superconducting down to the lowest temperature measured. [Preview Abstract] |
|
V1.00184: FLUIDS |
|
V1.00185: Using nanoparticles to control the speed of capillary filling in microchannels Yongting Ma, Olga Kuksenok, Amitabh Bhattacharya, Dennis Perchak, Anna C. Balazs Understanding the transport of multi-component fluids through porous medium is of great importance for a number of technological applications, ranging from ink jet printing, the production of textiles and enhanced oil recovery. Here, we examine the behavior of binary fluids containing nanoparticles that are driven by capillary forces to fill the microchannels. To carry out these studies, we use a hybrid computational approach that combines the lattice Boltzmann model for binary fluids and a Brownian dynamics model for the nanoparticles. We show that the nanoparticles dynamically alter both the interfacial tension between the two fluids and the contact angle in the microchannels; this, in turn, strongly affects the dynamics of the capillary filling. We demonstrate that by tailoring the properties of the nanoparticles, such as their affinity to the fluid components and their interaction with the microchannels, one can effectively control the filling velocities. Our findings provide fundamental insights into the dynamics of this complex multi-component system, as well as potential guidelines for a number of technological processes that focus on capillary filling with nanoparticles in porous media and microchannels. [Preview Abstract] |
|
V1.00186: Harnessing passive cilia arrays in ambient flow for anti-biofouling applications Anurag Tripathi, Amitabh Bhattacharya, Anna Balazs Active cilia arrays have been predicted to propel adhesive particles away from the surface and hence, could be used for antibiofouling applications (Bhattacharya et.al. Langmuir, 2012, 28, 3217). We explore the possibility of using non-actuated, passive cilia arrays for antibiofouling applications by utilizing the arrays' response to the ambient flow conditions. Using a hybrid computational model, we simulate a sticky biofouling spherical particle moving (under the influence of an applied force) towards the ciliated surface in an ambient fluid medium. Shear flow between parallel walls was simulated to mimic the ambient fluid flow dislodging the sticky particle from the surface. We obtain the minimum shear required to propel the sticky particle from the ciliated surface for different stickiness of the biofouling particle and stiffness of the cilia. The results are contrasted with adhesion to flat, non-ciliated surfaces and the important role of the cilia's response to the ambient flow condition is emphasized. [Preview Abstract] |
|
V1.00187: Viscosity measurements of nanoscale liquid films Edward Kramkowski, David Wilson, Shah Khan, Ashis Mukhopadhyay, Peter Hoffmann Measuring the viscosity of nanoscale films of liquids can be quite challenging. This difficulty has resulted in contradictory claims regarding the change in viscosity upon nanoscale confinement of liquids. Recently, we showed through a careful analysis, that in weakly interacting liquids, such as non-polar oils, the viscosity seems unchanged from the bulk value even under extreme confinement down to just a few molecular layers. Moreover, above a critical shear rate, shear thinning is observed. These measurements also have practical significance, in that traditional methods for characterizing the viscosity of solutions, while accurate, require the use of a few grams of the material being investigated. As the production methods of prototype materials becomes more costly, devising techniques that can accurately measure physical properties with much smaller volumes of material would be highly desirable. To this end, we aim to design a quick, reliable, and cost-effective method of measuring viscosity through the use of an atomic force microscope, which requires only nanograms of the sample being tested. Here we will introduce preliminary results, comparing the AFM-determined viscosity with values attained through the use of other commonly used measurement devices. [Preview Abstract] |
|
V1.00188: Measuring the effects of large scale intermittency on the small scales of turbulent flows Chen-Chi Chien, Daniel Blum, Greg Voth In standard cascade picture of 3D turbulent flows, energy is injected at a constant rate at large scales. It then is transferred to smaller scales by triad interactions that result from the non-linearity of the Navier-Stokes equation. The down-scale transfer is intermittent, and a vast literature has explored the signatures of this internal intermittency on statistics of the small scales. However, the energy injection at large scales is not constant in most real turbulent flows. We explore the signatures of this large scale intermittency on small scale turbulence statistics. Measurements were made in a flow between oscillating grids. By modulating grid frequency we introduce temporal variations in the injected energy which allows us to control the level of large scale intermittency. We find that the non-dimensional ratio of second to third order structure function depends on the degree of large scale intermittency, and we can quantitatively predict this ratio from the measured time dependence of the energy at large scales. Large scale intermittency can also be observed by conditioning Eulerian structure functions on the large scale velocity. Quantifying this dependence provides an alternative measurement of large scale intermittency which agrees with the structure function ratio. [Preview Abstract] |
|
V1.00189: A ``Cyber Wind Facility'' for HPC Wind Turbine Field Experiments James Brasseur, Eric Paterson, Sven Schmitz, Robert Campbell, Ganesh Vijayakumar, Adam Lavely, Balaji Jayaraman, Tarak Nandi, Pankaj Jha, Alex Dunbar, Javier Motta-Mena, Brent Craven, Sue Haupt The Penn State ``Cyber Wind Facility'' (CWF) is a high-fidelity multi-scale high performance computing (HPC) environment in which ``cyber field experiments'' are designed and ``cyber data'' collected from wind turbines operating within the atmospheric boundary layer (ABL) environment. Conceptually the ``facility'' is akin to a high-tech wind tunnel with controlled physical environment, but unlike a wind tunnel it replicates commercial-scale wind turbines operating in the field and forced by true atmospheric turbulence with controlled stability state. The CWF is created from state-of-the-art high-accuracy technology geometry and grid design and numerical methods, and with high-resolution simulation strategies that blend unsteady RANS near the surface with high fidelity large-eddy simulation (LES) in separated boundary layer, blade and rotor wake regions, embedded within high-resolution LES of the ABL. CWF experiments complement physical field facility experiments that can capture wider ranges of meteorological events, but with minimal control over the environment and with very small numbers of sensors at low spatial resolution. I shall report on the first CWF experiments aimed at dynamical interactions between ABL turbulence and space-time wind turbine loadings. Supported by DOE and NSF. [Preview Abstract] |
|
V1.00190: Jumping-Droplet-Enhanced Condensation on Scalable Superhydrophobic Nanostructured Surfaces Nenad Miljkovic, Ryan Enright, Youngsuk Nam, Ken Lopez, Nicholas Dou, Jean Sack, Evelyn Wang When droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump from the surface due to the release of excess surface energy. If designed properly, these superhydrophobic nanostructured surfaces can not only allow for easy droplet removal at micrometric length scales during condensation but promise to enhance heat transfer performance. However, the rationale for the design of an ideal nanostructured surface, as well as heat transfer experiments demonstrating the advantage of this jumping behavior are lacking. Here, we show that silanized copper oxide surfaces created via a simple fabrication method can achieve highly efficient jumping-droplet condensation heat transfer. We experimentally demonstrated a 25{\%} higher overall heat flux and 30{\%} higher condensation heat transfer coefficient compared to state-of-the-art hydrophobic condensing surfaces at low supersaturations. This work not only shows significant condensation heat transfer enhancement, but promises a low cost and scalable approach to increase efficiency for applications such as atmospheric water harvesting and dehumidification. Furthermore, the results offer insights and an avenue to achieve high flux superhydrophobic condensation. [Preview Abstract] |
|
V1.00191: Hematocrit and flow rate regulate the adhesion of platelets to von Willebrand factor Hsieh Chen, Jennifer Angerer, Matthias Schneider, Alfredo Alexander-Katz Here we present theoretical and experimental results showing that under the action of flow the adhesion probability of platelets to von Willebrand factor coated surfaces is strongly dependent on the hematocrit and flow rate. Interestingly, from experiments we observed that the actual binding forces are not markedly different, which suggest that the origin of such behavior is in the distribution of platelets. The experimental findings were solidly supported by explicit hydrodynamic simulations as well as stochastic differential equation simulations. We proposed a platelet transport model that, to our best knowledge, is the first in this field to have exact mathematical connections to the red blood cell distributions and shear rates. These findings present an important advance in understanding the dependence of blood clotting on hematocrit and can lead to advances in the treatment of vascular diseases associated with high levels of red blood cells. Furthermore, from the technological side the results presented here are important in areas where fine control of the separation of different classes of colloids is desired. [Preview Abstract] |
|
V1.00192: Numerical simulations of flagellated micro-swimmers and ciliated surfaces Henry Shum, Anurag Tripathi, Julia Yeomans, Anna Balazs Cilia are filamentous organelles found in many organisms for achieving locomotion or for driving fluid flows within the body. Cilia-like structures can be constructed and have potential for application in microfluidics, where they may be used to locally control flow and the motion of particles in the fluid. We implement a lattice Boltzmann method to simulate fluid flows produced by externally actuated artificial cilia and explore the influence of such cilia on objects in the surrounding fluid. In particular, we show examples of interactive effects between cilia arrays and self-motile swimmers propelled by a rotating helical flagellum. Artificial swimmers mimicking the motion of flagellated bacteria in this way have been experimentally realized in recent years and our simulations produce testable predictions for the behavior of such swimmers in the presence of cilia. [Preview Abstract] |
|
V1.00193: Modeling the swimming of microbes in anisotropic fluids Madison Krieger, Saverio Spagnolie, Thomas Powers Microbes commonly swim in non-Newtonian fluids such as mucus, soil, and tissue. Some of these complex fluids are characterized by long-chain molecules which can align, leading to anisotropy. We study a simple model of swimming in an anisotropic fluid, that of an infinitely long two-dimensional sheet deforming via propagating waves and immersed in a nematic liquid crystal. The liquid crystal is categorized by the dimensionless Ericksen number, which compares viscous and elastic effects. At infinite Ericksen number, where viscous effects dominate over elastic effects and the only time scale is the period of the propagating wave, we calculate the swim- ming speed and power dissipation as a function of the anisotropic viscosities and the tumbling parameter. We also calculate the swimming speed and power dissipation at finite Ericksen number, where the orientation elasticity introduces an additional time scale, the relaxation time. [Preview Abstract] |
|
V1.00194: Development of a microfluidics model for studying migration of sperm in the female reproductive tract Chih-kuan Tung, Florencia Ard\'{o}n, Mingming Wu, Susan S. Su\'{a}rez Infertility is a significant issue, both for humans and dairy cattle. In order for fertilization to happen, sperm must migrate through the female reproductive tract to reach the egg in the oviduct (fallopian tube). There is strong evidence that sperm interact with the female tract via both chemical and physical mechanisms. In this work, we focus on how the physical environment of the female tract influences the migration of bull sperm, which also serve as models for human sperm. In order for bull and human sperm to pass from the vagina into the uterus, they must swim through the cervical canal, which is lined by microchannels. Then, sperm must swim through the uterotubal junction, which also contains microchannels, in order to reach the oviduct. In both passageways, sperm must swim against a fluid flow, which would be less in the microchannels than in the central passageways. We have developed a microfluidic model for studying the sperm migration effects of the geometry of the cervix and uterotubal junction and the fluid flow within. [Preview Abstract] |
|
V1.00195: Swimming near a deformable interface Marcelo A. Dias, Thomas R. Powers It is a known fact that swimmers behave differently near deformable soft tissues than when near a rigid surface. Motivated by this class of problems, we investigate swimming microorganisms near flexible walls. We calculate the speed of a n infinitely long swimmer near an interface between two viscous fluids. Part of the calculation of the speed is the calculation of the shape of the free boundary. The swimming speed is controlled by the competition between surface and viscous effects, where two limits are observed. When the surface tension vanishes, we get Taylor's result for a swimmer with no walls. When the surface tension is infinite, the problem is like that of a swimmer near a rigid wall. [Preview Abstract] |
|
V1.00196: STATISTICAL AND NONLINEAR PHYSICS |
|
V1.00197: ABSTRACT HAS BEEN MOVED TO W30.00011 |
|
V1.00198: Local Elastic Fields in Granular Solids Dietrich Wolf, Jens Boberski, Lothar Brendel The modeling of elastic properties of disordered or granular solids requires a theory of elasticity that takes non-affine deformations into account. Using a linearized force law the non-affine elastic deformations are calculated. Base on the microscopically exact expressions for the local strain and stress fields (I. Goldhirsch, Granular Matter 12, 239 (2010)) a way to calculate maps of the local linear elastic constants for frictional granular packings is presented. The elastic constants are found to be scale and system size independent within an appropriate parameter range. [Preview Abstract] |
|
V1.00199: Pore pressure control on slope failure of a saturated granular step Yao You, Peter Flemings, David Mohrig Slope failure of granular sand and silt in water controls the release of sediments on the continental shelf and is an important process that delivers sand and silt into deep sea. Here we present a type of slope failure where the sediment grains are released in two modes: grain by grain release and collapsing of a slice that is a few hundred times grain diameter wide. We use flume experiments and pore pressure measurements to show that this type of slope failure is controlled by the generate and dissipation of pore pressure. The grain to grain release is associated with low pore pressure in the deposit, and collapsing of a slice occurs when the abnormally low pore pressure drains to a critical threshold. Collapsing of a slice generates pore pressure drop, which returns the mode of slope failure to grain by grain release. [Preview Abstract] |
|
V1.00200: How does money memorize social interactions? Understanding time-homogeneity in monetary systems Dieter Braun, Matthias Schmitt, Andreas Schacker Understanding how money shapes and memorizes our social interactions is central to modern life. There are many schools of thought on as to how monetary systems contribute to crises or boom/bust cycles and how monetary policy can try to avert them. We find that statistical physics gives a refreshing perspective [1-3]. We analyze how credit mechanisms introduce non-locality and time-heterogeneity to the monetary memory. Motivated by an analogy to particle physics, locality and time-homogeneity can be imposed to monetary systems. As a result, a full reserve banking system [4] is complemented with a bi-currency system of non-bank assets (``money'') and bank assets (``antimoney''). Payment can either be made by passing on money or by receiving antimoney. As a result, a free floating exchange rate between non-bank assets and bank assets is established. Interestingly, this monetary memory allows for credit creation by the simultaneous transfer of money and antimoney at a negotiated exchange rate. We analyze this novel mechanism of liquidity transfer in a model of random social interactions, yielding analytical results for all relevant distributions and the price of liquidity under the conditions of a fully transparent credit market.\\[4pt] [1] European Physical Journal B 17, 723729 (2000).\\[0pt] [2] Reviews of Modern Physics 81, 1703 (2009).\\[0pt] [3] Physica A 321, 605--618 (2003).\\[0pt] [4] Ryan-Collins, Greenham, Werner, Jackson, Where Does Money Come From? positivemoney.org.uk. [Preview Abstract] |
|
V1.00201: Why is the bulk modulus of jammed solids and granular packings much larger than the shear modulus? Alessio Zaccone, Denis Weaire In granular packings and metallic glasses, the rigidity to compression is much more pronounced than with respect to shear, resulting in the bulk modulus being much larger than the shear modulus. This state of affairs becomes dramatic in marginal jammed solids which are solid-like to compression but not to shear (Ellenbroek, Zeravcic, van Saarloos, van Hecke, EPL 87, 34004 (2009)). For metallic glasses, it was argued by Weaire et al. some time ago (Acta Metall. 19, 779 (1971)) that this effect might be due to the nonaffinity of the particle displacements. These arise because the force acting on a particle upon strain as a result of the strain-induced motion of its neighbors is not balanced in the absence of local order. Hence the particles undergo nonaffine displacements to relax these forces to the expense of the elastic storage energy, leading to lower values of the elastic moduli. Using the nonaffine theory of Zaccone and Scossa-Romano (PRB, 83, 184205 (2011)) we found a conclusive solution to this long standing problem. We show that in packings and related materials the excluded volume between neighbors induces geometric correlations which significantly reduce the nonaffinity under compression but leave the nonaffinity in shear substantially unaltered. [Preview Abstract] |
|
V1.00202: Ideal strength and structural instability of aluminum at finite temperatures Yi Zhang, Changfeng Chen, Wei Zhou, Hong Sun Understanding the mechanical strength and stability of materials under different external conditions is of critical importance to material science and engineering. Despite of the extensive efforts on 0K ideal strength calculations in the past decade, the temperature effects on the ideal strength and dynamical stability have not been explored. We have calculated the ideal strength of aluminum at finite temperatures by implementing an ab initio molecular dynamics method (AIMD) that treats elastic instability, dynamic instability, and thermodynamics in a unified first-principles approach. The results reveal significant changes in fundamental mechanical properties of aluminum: (i) the ideal strength drops precipitously with increasing temperature, by as much as 60\% at room temperature compared to T=0 K; (ii) the structural instability modes change qualitatively from dynamic phonon softening at low temperature to elastic failure at high temperature; (iii) the highly anisotropic low-temperature tensile strength becomes considerably more isotropic with rising temperature. Phonon calculations predict the disappearance of soft phonon modes near room temperature due to phonon anharmonic interactions, in excellent agreement with the AIMD results. [Preview Abstract] |
|
V1.00203: Composite Random Fiber Networks Catalin Picu, Ali Shahsavari Systems made from fibers are common in the biological and engineering worlds. In many instances, as for example in skin, where elastin and collagen fibers are present, the fiber network is composite, in the sense that it contains fibers of very different properties. The relationship between microstructural parameters and the elastic moduli of random fiber networks containing a single type of fiber is understood. In this work we address a similar target for the composite networks. We show that linear superposition of the contributions to stiffness of individual sub-networks does not apply and interesting non-linear effects are observed. A physical basis of these effects is proposed. [Preview Abstract] |
|
V1.00204: Soft-Nano-Materials: Extreme Mechanics at Extreme Length Scales Xuanhe Zhao Over decades of intensive research, various technologies have been developed to manufacture large-scale nanomaterials such as nanoparticles, quantum dots, nanowires, carbon nanotubes, biomolecules, nanofilms, and graphene. Meanwhile, extraordinary properties and functionalities of nanomaterials have been demonstrated by harnessing their deformations and instabilities coupled with their small length scales. However, a grand challenge still exists on how to control the deformations and instabilities of large-scale nanomaterials for scaling-up functions and applications that can impact the society. An emerging paradigm that addresses this challenge is by using soft materials such as polymers, gels and biomaterials to assemble large amounts of nanomaterials and regulate their deformations and instabilities in controlled manners. Successful examples range from nanostructured tissues such as bones and cartilages found in nature to polymer composites with nanowire/nanotube/graphene, flexible electronics, nano-generators and nano-batteries. This talk is focused on extreme mechanics of these soft-nano-materials and systems. We will discuss large deformation, instabilities, and fractures of one-dimensional and two dimensional nanomaterials, such as nanowires and graphene, interacting with matrices of soft materials. We will further illustrate extraordinary properties and functions achieved by understanding and exploiting the extreme mechanics of soft-nano-materials and systems. [Preview Abstract] |
|
V1.00205: Radial Elasticity and Friction Properties of Multiwalled Boron Nitride Nanotubes Investigated by Atomic Force Microscopy Hsiang-Chih Chiu, Elisa Riedo Boron Nitride nanotube (BNNT), similar to Carbon nanotube (CNT), has a layered structure with alternating boron and nitride atoms in a honeycomb configuration. BNNTs have comparable mechanical properties with CNTs and are expected to have potential applications in Nano-Electro-Mechanical Systems (NEMS) and nanocomposites. Therefore, understanding their mechanical and frictional properties is crucial to the development of these novel applications. In this work, we study the radial elasticity and friction properties of multiwalled BNNTs by means of Atomic Force Microscopy (AFM). We find that the radial modulus of BNNT decreases nonlinearly with the inverse of its external radius,$ R_{\mathrm{ext}}$, until arriving at the transverse elastic modulus of bulk hexagonal BN for larger $R_{\mathrm{ext}}$ and number of layers.$^{\mathrm{1}}$ In addition, by sliding an AFM tip across (transverse sliding) and along (longitudinal sliding) the principal axis of the BNNT, we find a larger friction coefficient during the transverse sliding due to the transverse deformation of BNNT. The friction anisotropy, defined as the ratio of the transverse to the longitudinal friction forces per unit area, is found to increase with the nanotube-substrate contact area, estimated to be proportional to ($L_{\mathrm{NT}}R_{\mathrm{ext}})^{\mathrm{1/2}}$, where $L_{\mathrm{NT}}$ is the length of the nanotube.$^{\mathrm{2}}$ Our results provide a better understanding of the mechanical and frictional properties of BNNTs. [1] Appl. Phys. Lett. 101, 103109 (2012) [2] Nanotech. 23, 455706 (2012) [Preview Abstract] |
|
V1.00206: Collapse of Non-Rectangular Channels in a Soft Elastomer Daniel Tepayotl-Ramirez, Yong-Lae Park, Tong Lu, Carmel Majidi We examine the collapse of microchannels in a soft elastomer by treating the sidewalls as in- denters that penetrate the channel base. This approach leads to a closed-form algebraic mapping between applied pressure and cross-sectional deformation that are in strong agreement with ex- perimental measurements and Finite Element Analysis (FEA) simulation. Applications of this new approach to modeling soft microchannel collapse range from lab-on-a-chip microfluidics for pressure-controlled protein filtration to soft-matter pressures sensing. We demonstrate the latter by comparing theoretical predictions with experimental measurements of the pressure-controlled electrical resistance of liquid-phase Gallium alloy microchannels embedded in a soft silicone elas- tomer. [Preview Abstract] |
|
V1.00207: Nonlinear Geometric Effects in Bioinspired Multistable Structures Zi Chen, Qiaohang Guo, Kevin Chu, Steven Shillig, Chi Li, Wenzhe Chen, Larry Taber, Douglas Holmes Nature features many thin shell structures with spontaneous curvatures, where mechanical instabilities play important roles in the morphogenesis and functioning of the organisms. However, the large deformation and instability phenomena of shells due to geometric nonlinearity, which often arise in morphogenesis and nanofabrication, remain incompletely understood. Here, we create spontaneously curved shapes with pre-strains in tabletop experiments, and study their instabilities with a minimal theory based on linear elasticity. The development of such theoretical and experimental approaches will promote quantitative understanding of the morphogenesis of growing soft tissues, and meet the emergent needs of designing stretchable electronics, artificial muscles and bio-inspired robots. [Preview Abstract] |
|
V1.00208: Mixing entropy in Dean flows Petru Fodor, Brian Vyhnalek, Miron Kaufman We investigate mixing in Dean flows by solving numerically the Navier-Stokes equation for a circular channel. Tracers of two chemical species are carried by the fluid. The centrifugal forces, experienced as the fluid travels along a curved trajectory, coupled with the fluid incompressibility induce cross-sectional rotating flows (Dean vortices). These transversal flows promote the mixing of the chemical species. We generate images for different cross sections along the trajectory. The mixing efficiency is evaluated using the Shannon entropy. Previously we have found, P. S. Fodor and M. Kaufman, Modern Physics Letters B 25, 1111 (2011), this measure to be useful in understanding mixing in the staggered herringbone mixer. The mixing entropy is determined as function of the Reynolds number, the angle of the cross section and the observation scale (number of bins). Quantitative comparison of the mixing in the Dean micromixer and in the staggered herringbone mixer is attempted. [Preview Abstract] |
|
V1.00209: Fabrication and Characterization of High Aspect Ratio PMMA Membranes for Filtering and Sensing Applications Thomas Hoke We report on the fabrication and function of high aspect ratio membranes for filtering applications in micro fluidic devices. We describe a new technique that enables us to construct a 40-90 microns thick membrane spanning a 3mm hole in a poly methyl methacrylate (PMMA) substrate. Polydimethylsiloxane (PDMS) is used to fill the hole in the PMMA. Once a liquid monomer solution is flowed over the substrate and cured with photo-polymerization, the PDMS is then removed, leaving a thin membrane spanning the hole. Filters are made from these membranes by etching silica or nickel micro particles that are embedded in the monomer solution. One goal of this project is to quantify how variables such as particle concentration, particle size, and etch time affect the filter porosity. This was done with membranes embedded with SiO$_{2}$ by creating a series of filters with various bead sizes and etch times. SEM was used to measure the thickness and structure of the membrane, and dynamic light scattering (DLS) was used to measure the amount of particles removed from a controlled suspension. These filters could successfully filter out particles as small as 3-10 microns. We will also report on the use of Ni in the filters to filter out His-tagged proteins due to the fact that are attracted to Ni ions. [Preview Abstract] |
|
V1.00210: Dissipated work and fluctuation relations for non-equilibrium single-electron transitions Aki Kutvonen, Jukka Pekola, Tapio Ala-Nissil\"a We discuss a simple but experimentally realistic model system, a single-electron box (SEB), where common fluctuation relations can be tested for driven electronic transitions. We show analytically that when the electron system on the SEB island is driven to a non-equilibrium state by the control parameter (gate voltage), the common fluctuation relation (Jarzynski equality) is not valid due to dissipated heat even when the system starts at thermal equilibrium and returns to it after the drive has been stopped. We perform no feedback on the system. However, an integral fluctuation relation based on total entropy production works also in this situation. We perform extensive Monte Carlo simulations of single-electron transitions in the SEB setup and find good agreement with the theoretical predictions. [Preview Abstract] |
|
V1.00211: CYBERWAR-2012/13: Siegel 2011 Predicted Cyberwar Via ACHILLES-HEEL DIGITS BEQS BEC ZERO-DIGIT BEC of/in ACHILLES-HEEL DIGITS Log-Law Algebraic-Inversion to ONLY BEQS BEC Digit-Physics U Barabasi Network/Graph-Physics BEQS BEC JAMMING Denial-of-Access(DOA) Attacks 2012-Instantiations Master Race Huffmann, Edward Carl-Ludwig Siegel Newcomb-Benford(NeWBe)-Siegel log-law BEC Digit-Physics Network/Graph-Physics Barabasi et.al. evolving-``complex''-networks/graphs BEC JAMMING DOA attacks: Amazon(weekends: Microsoft I.E.-7/8(vs. Firefox): Memorial-day, Labor-day,\textellipsis ), MANY U.S.-Banks:WF,BoA,UB,UBS,\textellipsis instantiations AGAIN militate for MANDATORY CONVERSION to PARALLEL ANALOG FAULT-TOLERANT but slow(er) SECURITY-ASSURANCE networks/graphs in parallel with faster ``sexy'' DIGITAL-Networks/graphs:``Cloud'', telecomm: n-G,\textellipsis , because of common ACHILLES-HEEL VULNERABILITY: DIGITS!!! ``In fast-hare versus slow-tortoise race, Slow-But-Steady ALWAYS WINS!!!'' (Zeno). \textbraceleft Euler [{\#}s(1732)] $\sum $-$\prod $( )-Riemann[Monats. Akad. Berlin (1859)] $\sum $-$\prod $( )- Kummer-Bernoulli ({\#}s)\textbraceright -Newcomb [Am.J.Math.4(1),39 (81) discovery of the QUANTUM!!!]-\textbraceleft Planck (01)]\textbraceright -\textbraceleft Einstein (05)]-Poincar e [Calcul Probabilit\'{e}s,313(12)]-Weyl[Goett. Nach.(14); Math.Ann.77,313(16)]-(Bose (24)-Einstein(25)]-VS. --Fermi (27)-Dirac(27))-Menger [Dimensiontheorie(29)]-Benford [J.Am. Phil.Soc.78,115(38)]-Kac[Maths Stats.-Reason. (55)]- Raimi [Sci.Am.221,109(69)]-Jech-Hill [Proc.AMS,123,3,887(95)] log-function [Preview Abstract] |
|
V1.00212: Brain Connectivity Inference under Network Spatial Subsampling Selene da Rocha Amaral, Gilson Vieira, Luiz A. Baccala Neurophysiological time series analysis using functional Magnetic Resonance Magnetic Imaging (fMRI) data can be seen as tool to investigate how the complex networks of neuronal populations interact naturally leading to brain connectivity description issues where it is desirable to process as many simultaneous structures as possible to avoid misleading interaction inferences. Here we systematically use simulations to gauge how connectivity inference is affected when only subsets of network structures are considered through exploratory tools like Partial Directed Coherence (PDC) and confirmatory methods like Dynamic Causal Modeling (DCM). PDC is based on Granger causality and uses autoregressive models to expose the direction of information flow whereas DCM was proposed to characterize neural fMRI connectivity using prior knowlegde of possible connectivity structures. SPM software was used to simulate the full network fMRI data which was subject to realistic noise levels prior to analysis of network structure subsets. [Preview Abstract] |
|
V1.00213: Synchronization of coupled oscillators in the presence of noise and communication delays Luc Robichaud, Alain Hache The Kuramoto model of coupled oscillators has been shown to describe many collective phenomena such as synchronization in natural and artificial systems. There are many factors that determine whether a system can synchronize or not, including the coupling strength, the number and density of oscillators and their natural frequencies. In some cases, however, noise and communication delays must also be taken into account, as they can significantly limit a system's capacity to synchronize. In this work, we map the space of parameters where synchronization of an ensemble of oscillators is possible when noise and delays are present. Based on numerical results, we derive general conditions to predict the possible synchronization of any given system. The possibility and limits of using a single quantity to predict synchronization, the ``quality of information'', which is related only to noise and delay, is discussed. [Preview Abstract] |
|
V1.00214: Einstein Critical-Slowing-Down is Siegel CyberWar Denial-of-Access Queuing/Pinning/ Jamming/Aikido Via Siegel DIGIT-Physics BEC ``Intersection''-BECOME-UNION Barabasi Network/GRAPH-Physics BEC: Strutt/Rayleigh-Siegel Percolation GLOBALITY--to-LOCALITY Phase-Transition Critical-Phenomenon Otto Buick, Pat Falcon, G. K. Alexander, Edward Carl-Ludwig Siegel Einstein[Dover(03)] critical-slowing-down(CSD)[Pais, Subtle in The Lord; Life {\&} Sci. of Albert Einstein(81)] is Siegel CyberWar denial-of-access(DOA) operations-research queuing theory/pinning/jamming/\textellipsis /Read [Aikido, Aikibojitsu {\&} Natural-Law(90)]/Aikido(!!!) phase-transition critical-phenomenon via Siegel DIGIT-Physics (Newcomb[Am.J.Math. 4,39(1881)]-\textbraceleft Planck[(1901)]-Einstein[(1905)])-Poincare[Calcul Probabilit\'{e}s(12)-p.313]-Weyl [Goett.Nachr.(14); Math.Ann.77,313 (16)]-\textbraceleft Bose[(24)-Einstein[(25)]-Fermi[(27)]-Dirac[(1927)]\textbraceright -``Benford''[Proc.Am.Phil.Soc. 78,4,551 (38)]-Kac[Maths.Stat.-Reasoning(55)]-Raimi[Sci.Am. 221,109 (69);\textellipsis ]-Jech[preprint, PSU(95)]-Hill[Proc.AMS 123,3,887(95)]-Browne[NYT(8/98)]-Antonoff-Smith-Siegel[AMS Joint-Mtg.,S.-D.(02)] algebraic-inversion to yield ONLY BOSE-EINSTEIN QUANTUM-statistics (BEQS) with ZERO-digit Bose-Einstein CONDENSATION(BEC) ``INTERSECTION''-\underline {\textbf{\textit{BECOME}}}-\underline {\textbf{UNION}} to Barabasi[PRL 876,5632(01); Rev.Mod.Phys.74,47(02);\textellipsis ] Network /Net/GRAPH(!!!)-physics BEC: Strutt/Rayleigh(1881)-Polya(21)-``Anderson''(58)-Siegel[J.Non-crystalline-Sol.40,453(80); [Preview Abstract] |
|
V1.00215: Self-similarity of phase-space networks of frustrated spin models and lattice gas models Yi Peng, Feng Wang, Yilong Han We studied the self-similar properties of the phase-spaces of two frustrated spin models and two lattice gas models. The frustrated spin models included (1) the anti-ferromagnetic Ising model on a two-dimensional triangular lattice (1a) at the ground states and (1b) above the ground states and (2) the six-vertex model. The two lattice gas models were (3) the one-dimensional lattice gas model and (4) the two-dimensional lattice gas model. The phase spaces were mapped to networks so that the fractal analysis of complex networks could be applied, i.e. the box-covering method and the cluster-growth method. These phase spaces, in turn, establish new classes of networks with unique self-similar properties. Models 1a, 2, and 3 with long-range power-law correlations in real space exhibit fractal phase spaces, while models 1b and 4 with short-range exponential correlations in real space exhibit nonfractal phase spaces. This behavior agrees with one of untested assumptions in Tsallis nonextensive statistics. [Preview Abstract] |
|
V1.00216: Classical Acoustic Echoes in Model Glasses Justin Burton, Sidney Nagel For the last 40 years, the low-temperature excitations in glasses have traditionally been explained in terms of a distribution of dilute, two-level quantum states that are created by clusters of particles tunneling between two nearly degenerate ground states. Strong evidence for this model has come from ultrasonic saturation effects and acoustic echoes [1] observed in experiments. Recently, a classical analysis of vibrational modes in model glasses has shown that at low frequencies, the modes are quasi-localized and highly anharmonic [2]. Using molecular dynamics simulations, we show that this anharmonicity can produce an acoustic echo due to the shift in the mode frequency with increasing amplitude. We observe this both in jammed packings of spherical particles with finite-range, Hertzian repulsions, and in model glasses interacting with a Lennard-Jones potential. In contrast to pulse echoes in two-level systems, a distinguishing feature of these ``anharmonic echoes'' is the appearance of multiple echoes after two excitation pulses, a feature also observed in experiments.\newline\newline [1] B. Golding and J. E. Graebner. Phys. Rev. Lett. 37, 852 (1976).\newline [2] N. Xu, V. Vitelli, A. J. Liu, and S. R. Nagel. Europhys. Lett. 90, 56001 (2010). [Preview Abstract] |
|
V1.00217: Electoral Susceptibility and Entropically Driven Interactions Bassir Caravan, Gregory Levine In the United States electoral system the election is usually decided by the electoral votes cast by a small number of ``swing states'' where the two candidates historically have roughly equal probabilities of winning. The effective value of a swing state is determined not only by the number of its electoral votes but by the frequency of its appearance in the set of winning partitions of the electoral college. Since the electoral vote values of swing states are not identical, the presence or absence of a state in a winning partition is generally correlated with the frequency of appearance of other states and, hence, their effective values. We quantify the effective value of states by an {\sl electoral susceptibility}, $\chi_j$, the variation of the winning probability with the ``cost'' of changing the probability of winning state $j$. Associating entropy with the logarithm of the number of appearances of a state within the set of winning partitions, the entropy per state (in effect, the chemical potential) is not additive and the states may be said to ``interact.'' We study $\chi_j$ for a simple model with a Zipf's law type distribution of electoral votes. We show that the susceptibility for small states is largest in ``one-sided'' electoral contests and smallest in close contests. [Preview Abstract] |
|
V1.00218: Lattice Stability and Reflection Symmetry Azita Jovaini, Shigeji Fujita, Salvador Godoy, Hung-Cheuk Ho, Akira Suzuki The basic stability condition for a general crystal lattice is the availability of parallel material planes. If this condition is met, then phonons (quanta of lattice vibrations) can be generated and can stabilize the lattice. A triclinic (TCL) lattice has three sets of material planes containing atoms subjected to restoring stresses represented by Young and rigidity moduli. Longitudinal and transverse lattice vibrations obeying one-dimensional (1D) wave equations stabilized the lattice. The phonon distribution is highly directional. There can be no spherical distribution. Earlier we show [1] that the TCL lattice has no ${\mathbf k}$-vectors for electrons and it is is an intrinsic insulator. Consider next an orthorhombic lattice. This lattice has 3D phonons obeying a 3D wave equation with a Laplacian space-derivative. The phonon distribution is over a 3D anisotropic ${\mathbf k}$-space. PACS numbers: 61.50.Ah, 72.15.Eb, 72.20.-i\\[4pt] [1] S.~Fujita, A.~Jovaini, S.~Godoy, and A.~Suzuki, {\it Phys. Lett. A}, {\bf 376}, 2808 (2012). [Preview Abstract] |
|
V1.00219: Mechanical Stochastic Resonance Elliot Wainwright, John Lindner Noise and nonlinearity can produce a stochastic resonance that maximizes a system's output signal-to-noise ratio. Stochastic resonance has been observed in electronic, chemical, optical, magnetic, and biological systems. Here, we report stochastic resonance in a simple mechanical system consisting of a bistable pendulum driven by a harmonic oscillator and the broad-band noise of a flapping flag. [Preview Abstract] |
|
V1.00220: A State Dependent Potts Model Gabriell M\'at\'e, Ronald Dickman, Dieter W. Heermann Although the resolution of conventional confocal microscopy is limited, the images provided by this technique carry a tremendous amount of information. One of the most straightforward approaches to describe these images is to model them with a Potts model. However, in many cases the detected configurations correspond to a system characterized by a temperature close to the critical point, making it almost impossible to control this model. In this work we present a modified version of the Potts model which might be useful in such situations. The modification consists in introducing arbitrary couplings between different states. We argue that in the simplest case the modified model is equivalent to the original Potts model. We investigate it numerically with respect to criticality and observe a shift of the critical point as we vary the parameters. We also show that the model is capable of exhibiting more exotic behavior. [Preview Abstract] |
|
V1.00221: Boundary Effects in Transmission through Random Media Xiaojun Cheng, Chushun Tian, Azriel Genack Recent measurements of the transmission matrix in disordered quasi-1D samples found the average of the logarithms of the transmission eigenvalues to be uniformly spaced. This corresponds to a single peak in the distribution of transmission eigenvalues at low values of transmission, which differs from the bimodal distribution with peaks at both high and low values. One of the reasons may be the reflectivity at the boundaries. The photon diffusion model suggests that internal reflection can be treated as extrapolation length and the average transmission behaves the same way as we change the sample length or the extrapolation length at the output, but it does not predict the impact of internal reflection on the distribution of the transmission eigenvalues. We have conducted microwave experiments and first-principles analytic calculations using the supersymmetry method to explore the role of boundary effects upon the transmission eigenchannels. Our results, however, show that the statistics of the transmission eigenchannels can be changed by reflectivity at the boundaries. The universality of the bimodal distribution breaks down in that channels with transmission close to unity are greatly suppressed when the extrapolation length is comparable to the sample length. [Preview Abstract] |
|
V1.00222: Approaching equilibrium: The evolution of CO$_2$ in a porous medium Yossi Cohen, Daniel H. Rothman Understanding the microscopic mechanisms of mineral weathering rates has motivated studies of dissolution and precipitation for decades. Many applications, including the global carbon cycle and sub- surface carbon dioxide sequestration justify the importance of a full comprehension of the mechanism. The injection of carbon dioxide into a porous medium drives the system into far-from-equilibrium conditions where forces, surface phenomena, and other processes become crucial for the long-term stability of the system. A complete physical picture able to predict the pattern formation and the structure developing within the porous medium is lacking and cannot be associated only with empirical kinetic laws. Here we propose a theoretical model that couples transport, reaction, and the intricate geometry of the rock. The model concerns the different time scales when the system is far from equilibrium and when approaching a steady state. We use analytical theory and numerical simulations to study the short and the long term behavior of the carbon dioxide as it dissolves and precipitates in a fluid-rock system. [Preview Abstract] |
|
V1.00223: Explosive percolations on a two-dimensional lattice and bond-site duality Woosik Choi, Soon-Hyung Yook, Yup Kim The site and bond explosive percolation models are carefully defined and studied on a square lattice. From the cluster distribution function and the behavior of the second largest cluster, it is shown that the duality in which the transition is discontinuous exists for the pairs of the site model and the corresponding bond model which relatively enhances the intra-bond occupation. In contrast the intra-bond-suppressed models which have no corresponding site models undergo the continuous transition and satisfy the normal scaling ansatz as ordinary percolation. [Preview Abstract] |
|
V1.00224: GENERAL THEORY/COMPUTAITONAL PHYSICS |
|
V1.00225: Photon-induced Spin Tunneling in Giant Molecules Coupled to Superconducting Resonators M.-Y. Tsang, M. Scheffler, M. Dressel, L. Bogani We present a model of magnetization relaxation of Mn12-acetate strongly coupled with photonic cavity resonator in low-temperature regimes (T $\leq$ 1K), a model based on photon-assisted-spin-tunnelling-induced, quartic magnetic anisotropy, on weak transverse magnetic fields and on photonic excitations. With the model, one calculates the spin-tunnelling rate as a function of the longitudinal magnetic field, whence we further determine the transition probability of a trapped photon as a function of both photon energy and external transverse magnetic field strength. This research is supported by the Sofja Kovalevskaja prize and German DFG (SFB-TRR21 and SPP1601). [Preview Abstract] |
|
V1.00226: Full Configuration Interaction Quantum Monte Carlo: The Use of Spin-pure and Non-Orthogonal Spaces Simon Smart, Nick Blunt, George Booth, Ali Alavi Full configuration interaction quantum Monte Carlo$^1$ (FCIQMC) allows for exact results to be obtained for the ground state within a finite-basis approximation of the Schr\"{o}dinger equation. Working within imposed symmetry constraints permits dramatic reductions in the size of the Hilbert space considered, reducing the computational cost, as well as permitting exclusion of the natural ground-state to extract a series of excited states of the system. All converged solutions are eigenfunctions of $\hat{S}^2$ as well as the Hamiltonion and projected spin. Working within a spin-pure basis allows this property to be used in the same manner as other imposed symmetries. FCIQMC requires frequent calculation of Hamiltonian matrix elements between random pairs of basis functions. In order to make use of an efficient scheme$^2$ for calculating these matrix elements between spin-projected basis functions, FCIQMC has had to be extended to work in non-orthogonal (and optionally non- normalised) bases. This has consequences for our understanding of the nature of spawning and death within FCIQMC. ~\\ $^1$ G. H. Booth, A. Thom, and A. Alavi, J. Chem. Phys. 131 054106 (2009) \\ $^2$ F. E. Harris, J. Chem. Phys. 46, 2769 (1967) [Preview Abstract] |
|
V1.00227: State-of-the-art molecular applications of full configuration interaction quantum Monte Carlo Robert E. Thomas, Catherine Overy, James J. Shepherd, George H. Booth, Ali Alavi Full configuration interaction quantum Monte Carlo (FCIQMC)$^1$ and its initiator adaptation (\emph{i}-FCIQMC)$^2$ provide, in principle, exact (FCI) energies \emph{via} a population dynamics algorithm of an ensemble of discrete, signed walkers in Slater-determinant space. We demonstrate that a novel choice of reference state has the potential to widen the scope of this already versatile method, and corroborate the finding that an extension of the algorithm to allow non-integer walkers can yield significantly reduced stochastic error without a commensurate increase in computational cost$^3$. New applications of FCIQMC to transition-metal systems of general and biological interest are presented, many of which have, to date, posed serious challenges for traditional quantum chemical methods$^4$$^5$. $^1$ G. H. Booth, A. J. W. Thom, and A. Alavi, J. Chem. Phys., 131, 054106 (2009) $^2$ D. M. Cleland, G. H. Booth, and A. Alavi, J. Chem. Phys., 132, 041103 (2010) $^3$ F. R. Petruzielo, A. A. Holmes, H. J. Changlani, M. P. Nightingale and C. J. Umrigar, arXiv:1207.6138 $^4$ N. B. Balabanov and K. A. Peterson, J. Chem. Phys., 125, 074110 (2006) $^5$ C. J. Cramer, M. Wloch, P. Piecuch, C. Puzzarini and L. Gagliardi, J. Phys. Chem. A, 110, 1991 (2006) [Preview Abstract] |
|
V1.00228: Measuring the Quality of Generalized Gradient Approximations in a Density Functional Theory Pseudopotential Environment for Solids Zachary Nault, Antonio Cancio Much recent development in DFT has focused on improving GGAs. Two schemes are second order GGA (SOGGA) and the APBE which builds the GGA from atomic systems and not the HEG. Both of these have been tested within an all electron (AE) environment, providing the most accurate results. The focus of many simulations, however, is on large systems using pseudopotentials (PsP's). Are these PsP calculations, which rely on functionals tested in an AE environment, accurately reproducing the AE ground state properties? If not, can the deficiencies be identified? To assess this, we use the PsP generator APE, using the functional library libXC which works with the PsP package ABINIT and the AE package Elk. We generate standard Troullier-Martin PsP's based on common and new XC functionals (LDA, PBE, PBEsol, APBE, SOGGA) and test their performance in 13 solids (Na, Li, Al, C, Si, GaAs, NaCl, LiF, LiCl, Cu, Pd, Rh, and Ag). We measure how well three ground state properties (lattice constant, bulk modulus, and cohesive energy) are calculated with PsP's as compared to the corresponding AE calculations. [Preview Abstract] |
|
V1.00229: An Automatic K-Point Grid Generation Scheme for Enhanced Efficiency and Accuracy in DFT Calculations Kyle McGill, Tim Mueller We seek to create an automatic k-point grid generation scheme for density functional theory (DFT) calculations that improves the efficiency and accuracy of the calculations and is suitable for use in high-throughput computations. Current automated k-point generation schemes often result in calculations with insufficient k-points, which reduces the reliability of the results, or too many k-points, which can significantly increase computational cost. By controlling a wider range of k-point grid densities for the Brillouin zone based upon factors of conductivity and symmetry, a scalable k-point grid generation scheme can lower calculation runtimes and improve the accuracy of energy convergence. [Preview Abstract] |
|
V1.00230: Charge Transfer Couplings and Excitation Energies From Subsystem DFT: The Ultimate Divide and Conquer Approach to DFT Michele Pavanello The subsystem formulation of DFT known as Frozen Density Embedding (FDE) offers an excellent platform for studying charge transfer reactions in solvated systems, such as biosystems. I present new theory and software development for the calculation of the electronic couplings as well as the charge transfer excitations from FDE derived densities. The method presented scales linearly with the number of non-covalently bound subsystems considered in the calculation. Proof-of-principle calculations of water and ethylene clusters with up to 56 monomers are presented. In addition, DNA oligomers radical cations, including donor-acceptor, donor-bridge-acceptor, as well as a prototype of the phothosynthetic reaction center are tackled and preliminary results are presented. [Preview Abstract] |
|
V1.00231: An investigation of the internal sum convergence in the full potential multiple scattering theory Yang Wang, Aurelian Rusanu, G. Malcolm Stocks, J. Sam Faulkner The ab initio methods based on multiple scattering theory (MST) have proved to be a very powerful technique for the electronic structure calculation for solids. The latest advances in the implementation of full potential MST have allowed us to investigate dislocations, point defects, and radiation damage effects on the physical properties of structural materials. In the conventional formulation of full potential MST, the single site wavefunctions $\phi_{l,m}$ are expanded in terms of spherical harmonics with angular momentum $l$ up to a cutoff value $\phi$-$l_{\rm max}$. This cutoff value defines the extension of the internal sum and is usually taken to be the same as KKR-$l_{\rm max}$, the cutoff value for the Bloch wave expansion (in terms of $\phi_{l,m}$) so that the single site sine and cosine scattering matrices used for calculating the $t$-matrix and the Green function are square matrices. In this presentation, we show a technique that allows for $\phi$-$l_{\rm max}$ to be greater than KKR-$l_{\rm max}$, so to allow for converging the internal sum, while keeping the calculation of the $t$-matrix and the Green function tractable. We compare the results obtained from different $\phi$-$l_{\rm max}$ values and discuss the implications of the internal sum convergence. [Preview Abstract] |
|
V1.00232: Electronic states of carbon alloy catalysts and nitrogen substituent effects on catalytic activity Tomoyuki Hata, Hiroshi Ushiyama, Koichi Yamashita In recent years, Carbon Alloy Catalysts (CACs) are attracting attention as a candidate for non-platinum-based cathode catalysts in fuel cells. Oxygen reduction reactions at the cathode are divided into two elementary processes, electron transfer and oxygen adsorption. The electron transfer reaction is the rate-determining, and by comparison of energy levels, catalytic activity can be evaluated quantitatively. On the other hand, to begin with, adsorption mechanism is obscure. The purpose of this study is to understand the effect of nitrogen substitution and oxygen adsorption mechanism, by first-principle electronic structure calculations for nitrogen substituted models. To reproduce the elementary processes of oxygen adsorption, we assumed that the initial structures are formed based on the Pauling model, a CACs model and nitrogen substituted CACs models in which various points are replaced with nitrogen. When we try to focus only on the DOS peaks of oxygen, in some substituted model that has high adsorption activity, a characteristic partial occupancy state was found. We conclude that this state will affect the adsorption activity, and discuss on why partially occupied states appear with simplification by using an orbital correlation diagram. [Preview Abstract] |
|
V1.00233: Reflectance Anisotropy Spectroscopy(RAS) of Si(111)-(3x1)-Ag and Si(111)-c(12x2): Comparison of hybrid density functional theory and experiment Sofia Jorgji, John McGilp, Charles Patterson The atomic and electronic structures of the Si(111)-(3x1)-Ag surface have been investigated extensively by LEED, STM and electron spectroscopies. The atomic structure is believed to be a honeycomb chain plus channel (HCC) structure in which channels containing Ag atoms are separated by Si in honeycomb chains. Here we compare results of previous reflectance anisotropy spectroscopy (RAS) experiments with hybrid DFT simulations for the HCC structure. Results of RAS simulations are in very good agreement with RAS experiments and indicate that the HCC structure is likely to be correct. Surface state features responsible for the RAS signal are identified and the effect of dimerisation of Ag chains on the RAS spectrum is considered. [Preview Abstract] |
|
V1.00234: Theoretical study on electronic properties of 2D graphene-TiO2 nanocomposites Yasuyuki Masuda, Giacomo Giorgi, Koichi Yamashita In recent years, bidimensional graphene-TiO2 nanocomposite materials have attracted deep interest since their potential applicability in photocatalytic and photovoltaics. It is extremely appealing, indeed, the possibility of synthesizing a composite materials able to embody both the semiconducting properties of TiO2 monolayers and the excellent transport ones of graphene.The synthetic path, similarly to the electronic and optical properties of such nanocomposites, is nowadays considered a hot-topic in materials science. However, on the theoretical side, predictive results on the properties of a so promising material with device-oriented relevance are astonishingly very scarce.In this work, we focus on the impact that the mechanical stress at the interface formed by graphene and a monolayer of anatase (001)-oriented exerts on electronic and optical properties of the final nanocomposite. In order to perform such analysis, we have modeled and optimized, by means of Density Functional Theory, several graphene-TiO2 monolayer models, examining and reporting analogies and differences between models in presence and in absence of a direct chemical bond. In this poster presentation, we report the results of these calculations and the predicted electronic properties of these nanocomposites. [Preview Abstract] |
|
V1.00235: Investigation of the liquid Pb/Si(001) interface from ab initio molecular-dynamics calculations D.J. Gonzalez, J. Souto, M.M.G. Alemany, R.C. Longo, L.J. Gallego, L.E. Gonzalez The structure of liquid Pb on an ideal Si(001) surface was studied experimentally a decade ago by means of x-ray diffraction and the results were interpreted in terms of the presence of fivefold symmetry Pb structures captured transiently by the potential created by the unreconstructed Si(001) surface. We critically analyze this interpretation in the light of the results obtained in an extensive ab initio molecular dynamics study of a system comprising 314 Pb atoms and 175 Si atoms setup in 7 (001) ideal layers (a total number of 1956 valence electrons) in a slab geometry. The structure found for the first Pb layer is very different from that of bulk Pb, mostly consisting in one-dimensional lines. However, we do observe the possibility of forming transient structures, in particular icosahedral caps. [Preview Abstract] |
|
V1.00236: Ab initio molecular dynamics simulations of the static, dynamic and electronic properties of the liquid Bi-Pb alloy J. Souto, M.M.G. Alemany, L.J. Gallego, L.E. Gonzalez, D.J. Gonzalez We perform an ab initio molecular dynamics study of the static, dynamic and electronic properties of the liquid Bi-Pb alloy at three concentrations, including the eutectic one. This alloy is of particular technological interest for its possible use as coolant in fast reactors. Our predictions are in good agreement with the available experimental data. In particular, the computed total static structure factors reproduce accurately the neutron diffraction results, and the predicted adiabatic sound velocity and shear viscosity compare well with the experimental values. The partial dynamic structure factors exhibit clear side peaks indicative of propagating density fluctuations, and the longitudinal and transverse dispersion relations show several branches.The electronic density of states show that the liquid Bi-Pb alloy is a good metal, but with strong deviations from the free-electron parabolic curve. [Preview Abstract] |
|
V1.00237: Thermodynamic of cellulose solvation in novel solvent mixtures Ritankar Das Biomass contains abundant amounts of cellulose as crystalline microfibrils. A limiting step to using cellulose as an alternative energy source, however, is the hydrolysis of the biomass and subsequent transformation into fuels. Cellulose is insoluble in most solvents including organic solvents and water, but it is soluble in some ionic liquids like BMIM-Cl. This project aims to find alternative solvents that are less expensive and are more environmentally benign than the ionic liquids. All-atom molecular dynamics simulations were performed on dissociated glucan chains separated by multiple (4-5) solvation shells, in the presence of several novel solvents and solvent mixtures. The solubility of the chains in each solvent was indicated by contacts calculations after the equilibration of the molecular dynamics. It was discovered that pyridine and imidazole acted as the best solvents because their aromatic electronic structure was able to effectively disrupt the inter-sheet interactions among the glucan chains in the axial direction, and because perturbation of the solvent interactions in the presence of glucan chains was minimal. [Preview Abstract] |
|
V1.00238: Towards a metallic glass transition in $\alpha $-Al$_{2}$O$_{3}$: A role of pressure-induced amorphization Sanjeev K. Gupta, Prafulla Jha Pressure-induced amporphization has been observed experimentally in many electrically insulating materials, including oxides. In none of the cases, the pressure-induced amorphization has been accompanied by metallic conduction. Alumina is one of the most important ceramics of the modern age and has a large band gap of at ambient conditions. In this talk, we will present the results of the study on the behavior of alumina under increasing pressure using first principles plane wave method within the linear response approach. The crystal structure and associated equilibrium lattice constants for $\alpha $-Al2O3 were obtained by minimizing the calculated total energies as function of a lattice constant. Further, to calculate the entropy and other allied properties, we have used density functional perturbation theory (DFPT). The calculated results show that Al2O3 might turn to metallic glass at pressure achievable in a laboratory. [Preview Abstract] |
|
V1.00239: Nanomorphology of the interface between P3HT and SWNT Katsuhiko Nishimra, Mikiya Fujii, Ryota Jono, Koichi Yamashita Organic bulk-heterojunction photovoltaic devices are promising as energy harvesting device because of their mass-productivity, and shorter energy pay back time compared to silicon based solar cells. Poly-3-HexylThiophene (P3HT) and Phenyl C$_{61}$ Butyrate Metyl (PCBM) are an early successful material pair and yield high IPCE of 60\% to 80\%. Instead of PCBM, Single Walled carbon Nanotubes (SWNT) has also been examined as an electron acceptor material because SWNTs have good properties such as high carrier mobility, which ended with surprisingly low efficiency compared to P3HT and PCBM pair however. According to a recent study, the low efficiency is due to ultrafast recombination of the free carriers generated on the interface. Therefore, nanomorphology of the interface is important to inhibit the recombination of free carriers. We have computationally analyzed how the nanomorphology of the interface between P3HT and SWNT is formed and how molecular orbital or other molecular properties are affected by the morphology. We are going to report how side chains on P3HT effect the nanomorphology and electronic structure around the interface. [Preview Abstract] |
|
V1.00240: Semiconductor nano-gap antennas with high quality factor Mitsuharu Uemoto, Hiroshi Ajiki Metallic islands with nano-gap structure are one of the most popular optical antennas [1]. We theoretically propose a new nano-gap antenna utilizing exciton resonance of semiconductor. A light field at the nano-gap (hot spot) formed between two CuCl islands is significantly enhanced by a factor of metallic antennas. However, the hot spot of the semiconducting antenna exhibits much higher quality factor $(Q \approx 10^4)$ at $T=40$ K than those of metallic antennas which do not exceed $Q \approx 100$. Our result suggests the semiconducting antenna would function as a new type of photonic cavity. The calculation method is based on a finite element method which can take into account exciton resonance [2]. We also systematically study the geometry dependence of the enhancement factor and Q factor. In contrast to metallic antenna, blunt edges of semiconducting islands at the gap are preferable in order to achieve high enhancement factor. This is because of the fact that exciton wave function extends near the edge for blunt geometry.\\[4pt] [1] P. M\"uhlschlegel et al, Science 308, 5728, 1607-1609 (2005).\\[0pt] [2] M. Uemoto and H. Ajiki, in preparation. [Preview Abstract] |
|
V1.00241: Cross-sectional Characterization of All Solid State Thin Film Lithium Ion Batteries by Analytical Transmission Electron Microscopy Zhipeng LI, Shintaro Yasui, Joysurya Basu, Dmitry Ruzmetov, Alec Talin, Ichiro Takeuchi, Leonid Bendersky Recent years witnessed the fast development of microelectronic and micro energy storage devices, which require new batteries with lightweight and high energy densities. All solid state lithium ion batteries are considered as a promising candidate for power supply of such devices. In this study, all solid state thin film lithium ion batteries, consisting of a LiLaTiO$_{\mathrm{3}}$ electrolyte, Li$_{\mathrm{4}}$Ti$_{\mathrm{5}}$O$_{\mathrm{12}}$ anode, and LiCoO$_{\mathrm{2}}$ or compositionally graded Li(Mn/Ni)O$_{\mathrm{x}}$ cathodes, were fabricated by a pulsed laser deposition technique. Cross-sectional microbatteries were prepared by focus ion beam and traditional TEM sample preparation techniques. Detailed microstructures of microbatteries were performed using analytical TEM. Multilayer thin films of batteries were epitaxially grown on Nb doped SrTiO3 substrates which serve as current collectors. Microstructures of electrolyte and electrodes, and interfacial diffusions were studied before and after charge-discharge cycling. The mechanism of cycling-triggered microstructural evolution was elucidated accordingly. These findings can not only help improve the understanding of reliability of thin film battery fabrication/assembling processes, but also shed light on issues of battery degradation. This study technically lays the foundation for our ongoing work on in-situ investigation of microbattery cycling in TEM. [Preview Abstract] |
|
V1.00242: Laser-induced coherent population trapping in $\rm C_{60}$ Guoping Zhang, T. F. George Coherent population trapping and electromagnetically induced transparency represent important advancements in quantum optics and atomic physics, with broad applications from slowing and stopping light, quantum memory, photon control in quantum information processing, storage of light and information, to cancellation of Stark shifts in optical lattice clocks. In this talk, we demonstrates the possibility of generating coherent population trapping in $\rm C_{60}$. Similar to a three-level $\Lambda$ system, cm has a forbidden transition between the highest occupied molecular orbital (HOMO) ($|a\rangle$) and the lowest unoccupied molecular orbital (LUMO) ($|c\rangle$), but a dipole-allowed transition between HOMO and LUMO+1 ($|b\rangle$) and between $|b\rangle$ and $|c\rangle$. We employ two cw laser fields, one coupling and one probe. The strong coupling field is switched on first to resonantly excite the transition between $|b\rangle$ and $|c\rangle$. After a delay, the probe is switched on, such that the coherent interaction between the coupling and probe fields traps the population in $|a\rangle$ and $|c\rangle$. This forms a partially dark state in $\rm C_{60}$, analogous to that in atomic vapors. Turning off the coupling field restores $\rm C_{60}$'s absorption. Pulsed lasers [Preview Abstract] |
|
V1.00243: Shear band blocking in explosively driven collapse of corrugated Ni-Al laminate cylinder Karl Olney, Po-Hsun Chiu, Andrew Higgins, Matthew Serge, Gregory Fritz, Adam Stover, Vitali Nesterenko, David Benson Ni-Al laminate materials have been identified as a possible material system that can be used as a reactive material due to the self-sustaining reaction between Al and Ni layers. Besides traditional ignition methods, shear bands developed during mechanical loading can provide sites where ignition can occur. Corrugated Ni-Al laminate samples were created by swaging alternating layers of Ni (20 micrometers thick) and Al (30 micrometers thick) foils. The thick-walled cylinder (TWC) technique was performed on a corrugated Ni-Al laminate cylinder sample to examine shear band development in this material. Post experiment examination of the corrugated Ni-Al laminate material showed that the development of global shear bands were blocked via mesoscale mechanisms. The collapse of the corrugated laminate cylinder was simulated providing insight into these mesoscale mechanisms that were involved in blocking the development of shear bands during the experiment. Despite the shear band resistance of the material, several regions of the sample had localized reactions of Al and Ni spanning approximately 10-20 layers of laminate. [Preview Abstract] |
|
V1.00244: Ground state energy calculations of polynomial potentials based on Hamiltonian moments Melissa Hoffman, Robert Murawski, Jay Mancini, Vassilios Fessatidis, Samuel Bowen Recently, Martin et al calculated approximate energy eigenvalues for potentials of the form V(x) $=$ x$^{a} + \lambda $ x$^{b}$ by use of the multi-point quasi-rotational technique (Rev. Mex. Fis. \textbf{58}, 301 (2012)). In their paper, they considered specific values of $\lambda $ and integer values of $a$ and $b$. In this work, we shall apply a moments approach to study the general ground state energy of such potentials for arbitrary values of $\lambda $ and for integer and non-integer values of $a$ and $b.$ We will compare their results against the generalized moments expansion (GMX) in terms of accuracy and computational effort. In addition, we will calculate the energy spectrum with the Lanczos tridiagonalization technique. [Preview Abstract] |
|
V1.00245: Comparing new approaches for the real and imaginary time evolution of the Hubbard model Michael Moeckel Recent advances in the experimental realization and theoretical simulation of fermionic many-body systems have motivated new interest in the Hubbard model both under real and imaginary time evolution. The possibility to follow the dynamics of excited states in cold quantum gases loaded on optical lattices [1] allows to observe relaxation behavior of the Hubbard model under the influence of nonadiabatic parameter changes. On the other hand, initiator full configuration interaction quantum Monte Carlo (iFCIQMC) provides a promising new approach to an efficient sampling of the Hilbert space based on a mapping of imaginary time evolution onto a population dynamics in Slater determinant space [2]. Since characteristic features of the Hubbard model like time scale separation and long time transient behavior [3] become visible in both approaches I provide a comparison of related results.\\[4pt] [1] I. Bloch, J. Dalibard, W. Zwerger, Rev. Mod. Phys. 80, 885-964 (2008)\\[0pt] [2] G. H. Booth, A. Thom, A. Alavi, J. Chem. Phys. 131, 054106 (2009); D. Cleland, G. H. Booth, A. Alavi, J. Chem. Phys. 132, 041103 (2010)\\[0pt] [3] M. Moeckel, S. Kehrein, Phys. Rev. Lett. 100, 175702 (2008) [Preview Abstract] |
|
V1.00246: Monte Carlo simulation of single-molecule recycling in a nanochannel for accurate diffusion measurements Bo Wang, Sultan Behery, Lloyd M. Davis In previous experiments on single-molecule (SM) detection in solution, we demonstrated that prolonged observation times and photon yields are achieved by actively trapping a molecule in a nanochannel. We also developed Monte Carlo simulations to optimize experimental parameters and improve real-time control algorithms. Other researchers have since shown similar advantages can be attained by alternating the flow in the nanochannel so that a SM repeatedly passes through the laser excitation focus and that variation in the times between detections provides a measure of the diffusion coefficient of the molecules. We have extended the previous simulations to study the SM recycling experiment and to compare control algorithms and measurement capabilities in which the timing of each photon is processed by an FPGA circuit, as used in our trapping experiments, with those where detected photons are first collected into 1 ms bins, as in the prior recycling experiments. We present capabilities for measuring the diffusion coefficients of SMs. Also, we compare the capability for resolving a solution containing species with differing diffusion coefficients with that of fluorescence correlation spectroscopy, which is often used for monitoring molecular interactions in pharmaceutical research. [Preview Abstract] |
|
V1.00247: Modeling of nanoscale transport using fractional exclusion statistics George Alexandru Nemnes, Dragos Victor Anghel In recent years, with the continuous development of nanostructured materials, many-body quantum effects were observed in the charge, spin or phonon transport. Fractional exclusion statistics (FES) has already proved to be an important tool in the study of thermodynamical properties of interacting Bose and Fermi systems, which are regarded as ideal FES gases. Recently, the transition rates for FES gases were established [1], which opens the possibility of analyzing interacting boson and fermion systems in non-equilibrium. We make here a step further and introduce a transport model based on FES, using Monte Carlo simulations. The transport model based on FES is applied on quasi-1D systems, such as core-shell structures. The statistical FES parameters are extracted from the interacting electron gas, taking into account the Coulomb interaction. We also investigate transport in systems with quenched disorder [2]. Within our approach we are able to point out some particularities of charge transport of interacting fermions in nanoscale systems with multiple interfaces.\\[4pt] [1] G.A. Nemnes, D. V. Anghel, J. Stat. Mech. P09011 (2010) [2] G.A. Nemnes, D. V. Anghel, ``Fractional exclusion statistics in systems with localized states,'' J. Phys.: Conf. Series (accepted, 2012) [Preview Abstract] |
|
V1.00248: Electrohydrodynamic modeling of an electrospray-based thruster in cone-jet mode Manish Jugroot, Martin Forget, Cecile Malardier-Jugroot Electrospray-based propulsion is an excellent candidate for small satellites due to its inherent small size and high specific impulse. The present study aims to gain an increased understanding of complex underlying physical processes namely transitions. Numerical modeling and simulations can offer insights into the flows within the electrospray and offer critical local information difficult to measure experimentally due to the small scales. A multi-component continuum-based model coupling fluid dynamics, charged species dynamics and electric field is developed. The simulations describe the charged fluid interface with emphasis on the Taylor cone formation and cone-jet transition under the effect of a electric field. The goal is to recapture this transition from a rounded liquid interface into a Taylor cone from an initial uniform distribution, without making assumptions on the behaviour, geometry or charge distribution of the system, and transition to droplet or cone-jet mode. The time evolution of the interface highlights the close interaction among space charge, coulombic forces and the surface tension, which appear as governing and competing processes in the transition. Several modes and regimes are examined and compared to experimental results. The results from the coupled formalism provide valuable insights on the physical phenomena and will be applied to tailoring a multi-beam colloid thruster. [Preview Abstract] |
|
V1.00249: Construction of adiabatic connection curve for electron-hole system using multicomponent Levy-Lieb Lagrangian Jennifer Elward, Benjamin Kaplan, Arindam Chakraborty The electron-hole adiabatic connection curve (eh-ACC) is central in development of accurate correlation functional for multicomponent electron-hole density functional theory (eh-DFT). The construction of accurate eh-ACC is challenging because it requires density constrained energy minimization at different values of coupling constants. In the present work, the density constraint was avoided by defining an electron-hole Levy-Lieb Lagrangian (eh-LLL). For a given set of input electron and hole densities, the eh-LLL was constructed and expressed as a functional of the coupling constant dependent external potential. Unconstrained minimization of the eh-LLL was performed by varying the eh-wavefunction, external potential, and Lagrange's multipliers. An explicitly correlated ansatz was used for the eh-wavefunction and the search over the wavefunction was performed using variational Monte Carlo. The calculation was repeated for coupling constants in the range of 0 to 1 and the minimized wavefunction was used for construction of the eh-ACC. This study represents the first step in construction of accurate electron-hole correlation functional for eh-DFT. [Preview Abstract] |
|
V1.00250: Vacuum State Energies of Anharmonic Potentials by Method of Undetermined Amplitudes Samuel P. Bowen, Jay D. Mancini, Vassilios Fessatidis This is an examination of the applications of a method of undetermined amplitudes to the quantization of polynomial potentials leading to the determination of the exact vacuum state energies for several important potentials. The potentials studied include the simple harmonic oscillator (SHO) $x^{2}$, $x^{4}$, $x^{2n}$, $\pm x^{2}+x^{4}$, $\pm x^{2}+x^{6}$, $\pm x^{2}+x^{10}$ and others. The ground state and vacuum state energies are determined analytically and all have branch point singularities as functions of the coupling parameters and thus cannot be reached by perturbative series expansions. The excited state spectrum must usually be determined numerically, but is determined exactly for the systems where Bohr-Sommerfeld integrals can be solved for the energy. [Preview Abstract] |
|
V1.00251: Automatic sorting of point pattern sets using Minkowski Functionals Joshua Parker, Eilon Sherman, Matthias van de Raa, Larry Samelson, Wolfgang Losert Point patterns arise in many different areas of physical and applied research, often resulting in sets of patterns that may or may not be fundamenally different. We introduce here a automatable numerical taxonomy procedure for clustering point pattern sets using their approximated Minkowski functionals. We demonstrate that this procedure outperforms current methods, even when the patterns are drawn from very similar processes. We highlight the use of this routine for automatically analyzing sets of patterns, and in particular super-resolution images of fluorescently labeled proteins. Overall, we find that this routine is a robust method for sorting point pattern sets, and provides meaningful insight regarding the homogeneity of spatial processes. [Preview Abstract] |
|
V1.00252: Test of Relativity Theory Using Spinning Bodies in Low-Earth Orbit Ryan Everett, James Overduin Using measurements of geodetic precession around the Earth from Gravity Probe B, we constrain departures from Einstein's General Relativity for a spinning test body in Kaluza-Klein gravity with one additional space dimension. We consider two of three known time-independent, spherically symmetric solutions of the 5D field equations and obtain new constraints on the values of the free parameters associated with each metric. [Preview Abstract] |
|
V1.00253: Riemann-Hypothesis Millennium-Problem(MP) Physics Proof via CATEGORY-SEMANTICS(C-S)/F$=$C Aristotle SQUARE-of-OPPOSITION(SoO) DEduction-LOGIC DichotomY Joao-Joan Baez, Michelle Lapidaryus, Edward Carl-Ludwig Siegel Riemann-hypothesis physics-proof combines: Siegel-Antono\textregistered -Smith[AMS Joint Mtg.(2002)- Abs.973-03-126] digits on-average statistics HIll[Am. J. Math 123, 3, 887(1996)] logarithm-function's (1,0)- xed-point base$=$units$=$scale-invariance proven Newcomb [Am. J. Math. 4, 39(1881)]-Weyl[Goett. Nachr.(1914); Math. Ann.7, 313(1916)]-Benford[Proc. Am. Phil. Soc. 78, 4, 51(1938)]-law [Kac,Math. of Stat.-Reasoning(1955); Raimi, Sci. Am. 221, 109(1969)] algebraic-inversion to ONLY Bose-Einstein quantum-statistics(BEQS) with digit d $=$ 0 gapFUL Bose-Einstein Condensation(BEC) insight that digits are quanta are bosons because bosons are and always were quanta are and always were digits, via Siegel-Baez category-semantics tabular list-format matrix truth-table analytics in Plato-Aristotle classic "square-of-opposition" : FUZZYICS$=$CATEGORYICS/Category-Semantics, with Goodkind Bose-Einstein Condensation (BEC) ABOVE ground-state with/and Rayleigh(cut-limit of "short-cut method";1870)-Polya(1922)-"Anderson"(1958) localization [Doyle and Snell,Random-Walks and Electrical-Networks, MAA(1981)-p.99-100!!!] in Brillouin[Wave-Propagation in Periodic-Structures(1946) Dover(1922)]-Hubbard-Beeby[J.Phys.C(1967)] Siegel[J.Nonxline-Sol.40,453(1980)] generalized-disorder collective-boson negative-dispersion mode-softening universality-principle(G\textellipsis P) first use of the ``square-of-opposition'' in physics since Plato and Aristote!!! [Preview Abstract] |
|
V1.00254: Terrorism/Criminalogy/Sociology via Magnetism-Hamiltonian ``Models''?!: Black Swans; What Secrets Lie Buried in Magnetism?; ``Magnetism Will Conquer the Universe?''(Charles Middleton, aka ``His Imperial Majesty The Emperior Ming `The Merciless!!!'' Anthony Carrott, Edward Carl-Ludwig Siegel, John-Edgar Hoover, Elliott Ness Terrorism/Criminalogy//Sociology : non-Linear applied-mathematician (``nose-to-the grindstone / ``gearheadism'') ''modelers'': Worden, , Short, \textellipsis criminologists/counter-terrorists/sociologists confront [SIAM Conf. on Nonlinearity, Seattle(12); Canadian Sociology Conf,. Burnaby(12)]. ``The `Sins' of the Fathers Visited Upon the Sons'': Zeno vs Ising vs Heisenberg vs Stoner vs Hubbard vs Siegel ''SODHM''(But NO Y!!!) vs \textellipsis ??? Magntism and it turn are themselves confronted BY MAGNETISM,via relatively magnetism/metal-insulator conductivity / percolation-phase-transitions critical-phenomena -illiterate non-linear applied-mathematician (nose-to-the-grindstone/ ``gearheadism'' )''modelers''. What Secrets Lie Buried in Magnetism?; ``Magnetism Will Conquer the Universe!!!''[Charles Middleton, aka ``His Imperial Majesty The Emperior Ming `The Merciless!!!']''; magnetism-Hamiltonian phase-transitions percolation-``models''!: Zeno(\textasciitilde 2350 BCE) to Peter the Pilgrim(1150) to Gilbert(1600) to Faraday(1815-1820) to Tate (1870-1880) to Ewing(1882) hysteresis to Barkhausen(1885) to Curie(1895)-Weiss(1895) to Ising-Lenz(r-space/Localized-Scalar/ Discrete/1911) to Heisenberg(r-space/localized-vector/discrete/1927) to Priesich(1935) to Stoner (electron/k-space/ itinerant-vector/discrete/39) to Stoner-Wohlfarth (technical-magnetism hysteresis /r-space/ itinerant-vector/ discrete/48) to Hubbard-Longuet-Higgins (k-space versus r-space/ [Preview Abstract] |
|
V1.00255: POST-DEADLINE ABSTRACTS |
|
V1.00256: Laser Induced Fluorescence Spectroscopy of a Langmuir Monolayer of C-16 Fluorescent Dipyrrinone Liquid Crystal Christian Struebing, Giovanni DeLuca, Chandra Prayaga, Aaron Wade, Michael Huggins, Amy Renaud, Rebecca Chandler A C-16 Fluorescent Dipyrrinone Liquid Crystal synthesized by the Chemistry department, University of West Florida, has been~prepared in a Langmuir monolayer using a Nima Langmuir-Blodgett Trough. DeLuca et al. [1] studied how the length of the hydrocarbon tail influences the behavior of the pressure-area isotherm of the Langmuir film. The C-16 Fluorescent Dipyrrinone Liquid Crystal film produced a stable film at 20 mN/m and a stable, optical quality film at 40 mN/m.~We present a study of the fluorescence properties of the C-16 fluorescent dipyrrinone liquid crystal film. Once the monolayer is compressed the sample is excited using a 410 nm wavelength laser~and the fluorescence is measured using an Oriel MS260i 1/4 m Spectrograph. \\[4pt] [1] Deluca, Giovanni; Carroll, Alexander; Prayaga, Chandra; Wade, Aaron; Heath, Christopher; Renaud, Amy; Huggins, Michael. ``Preparation and Characterization of C-16 and C-10 Fluorescent Dipyrrinone Liquid Crystal Langmuir-Blodgett Films.'' American Physical Society, APS March Meeting 2012, 02/2012. [Preview Abstract] |
|
V1.00257: Electric-field-induced destruction of quasi-Landau levels in AA-stacked bilayer graphene nanoribbons Hsien-Ching Chung, Yu-Ming Wang, Ming-Fa Lin The magneto-electronic properties of AA-stacked bilayer zigzag graphene nanoribbons are investigated by the Peierls tight-binding method. In the presence of magnetic fields, Landau quantization leads to the partial dispersionless subbands, which are called quasi Landau levels (QLLs). For bilayer zigzag nanoribbons, there are two groups of QLLs with two pairs of partial flat subbands. A perpendicular electric field, serving as the top gate, is expected to push these QLLs to higher state energies and to split the flat subbands. Wave functions, providing more information on the electronic states, are employed to analyze the mixing Landau and localized states on the flat subbands. And the electron distributions of Landau subbands are also be presented. The density of states are discussed at last in detail. The aforementioned predicted properties could be verified through optical spectroscopy and scanning tunneling spectroscopy. [Preview Abstract] |
|
V1.00258: Role of Dirac cones in magneto-transport properties of REFeAsO (RE$=$rare earth) oxypnictides Fabio Bernardini, Ilaria Pallecchi, Federico Caglieris, Andrea Palenzona, Gianrico Lamura, Sandro Massidda, Marina Putti Dirac cone (DC) states are one of the most intriguing issues in condensed matter physics. Abrikosov showed that DC states can be identified by the low temperature behavior of the magneto-resistance. In additon to the usual quadratic dependence of ($\rho $(H)-$\rho $(H$=$0))/$\rho $(H$=$0) on magnetic field, a linear dependence appears in the presence of DC states. Such a behavior was discovered in experiments of magneto-resistance in BaFeAs and Pr(Ru,Fe)AsO supporting the existence of DC states in other iron-pnictides superconductors too. Here we investigate the issue of DC states in iron oxypnictides of composition REFeAsO (RE$=$rare earth). We carry out both ab-initio calculations of the band structure, which evidence the presence of mildly anisotropic Dirac cones along the Y-$\Gamma $ and Z-R directions of the reciprocal space and we explore transport behavior by means of resistivity, Hall resistance and magneto-resistance measurements, which confirm the dominant role of Dirac cones. By combining our theoretical and experimental approaches, we extract information on effective masses, scattering rates and Fermi velocities for different rare earth elements. [Preview Abstract] |
|
V1.00259: Vortex String in Electric Dipole Radiation near a Mirror Zachary Schulz, Xin Li, Henk Arnoldus When an atom, molecule or nanoparticle is irradiated by a laser beam, it will emit radiation, either as scattered light or resonance fluorescence. When the small particle is located near an interface, the emitted radiation will interfere with the reflected radiation, and this alters the radiation pattern. This problem was already studied by Sommerfeld in the 1950's, when he considered the effect of the Earth on the radiation pattern of dipole radiation emitted by an antenna. Many experimental and theoretical efforts have been devoted to this problem since, including quantum effects leading to alterations of the lifetime of atomic levels due to the presence of the interface. With the rapid progress of nanophotonics, where phenomena on the scale of an optical wavelength or less are of interest, this area of research has attracted renewed attention. It was recently shown that when dipole radiation is emitted near an interface, the mechanism of emission is drastically different from emission in free space. In addition, the flow pattern of the energy can be rather complicated, and it contains singularities and vortices as a result of the interference between the emitted light and the light reflected by the interface. [Preview Abstract] |
|
V1.00260: Factors Influencing the 2D Elastic Moduli of Self-Assembled Nanoparticle Monolayers Sihen You, Rossen Rashkov, Pongsakorn Kanjanaboos, Ignavio Calderon, Mati Meron, Heinrich Jaeger, Binhua Lin Nanoparticles with hydrophobic capping ligands are found to self-assemble into monolayer films when deposited on the air/water interface. Different nanoparticle monolayers exhibit a rich morphology of wrinkling, folding and buckling behavior that indicates interesting elastic properties. We obtain the 2D bulk and shear moduli of several different nanoparticle films by measuring the anisotropic stress response of the film under uniaxial compression using a Langmuir trough, a method previously applied to lipid and protein membranes. We find that the elastic properties of the nanoparticle film are affected by size distribution of the nanoparticles and the properties of their capping ligands. Higher polydispersity results in a greater number of packing defects that weaken the assembled film. The ligands mediate the particle-particle interaction, acting like elastic springs that join together hard spheres. The strength of such ``springs'' is determined by the degree of interdigitation of ligands between neighboring nanoparticles as well as the shapes of the capping ligands. These results suggest that the elastic moduli of nanoparticle films can be tuned through careful alteration of size distribution and capping ligand's shape and density. [Preview Abstract] |
|
V1.00261: Multiscale simulation for non-isothermal polymeric flow between parallel plates Shugo Yasuda, Ryoichi Yamamoto A multiscale simulation method for non-isothermal polymeric flow is developed based on the local stress sampling strategy and applied to the flows of a polymer melt in the simple creep motion of the parallel plates. In our multiscale modeling, the macroscopic quantities, e.g., density, velocity and temperature, are calculated by using a usual lattice-mesh based computational fluid dynamic (CFD) simulation, but, instead of using any constitutive equations, the local stresses are generated by performing the molecular dynamics (MD) simulations associated with each mesh interval of the CFD calculation according to the local macroscopic quantities. It is found that, at a rapid creep velocity, the distinct regimes in the velocity field appear between the vicinity and intermediate of the plates because the local viscosity drastically varies due to the temperature variation generated by the local viscous heating. The effect of density variation due to the thermal expansion and compressible flow on the flow field is also investigated. [Preview Abstract] |
|
V1.00262: Soft X-ray Scattering for Soft Materials at ALS Cheng Wang, Alexander Hexemer, Anthony Young, Howard Padmore The function and properties of organic and biological soft-condensed matter systems are largely determined by their nano- and mesoscopic chemical morphology. The understanding and rational use of such systems thus require that this structure be known. Using x-ray energies close to the absorption edge of constituent atoms, soft x-ray scattering is a combination of conventional x-ray scattering with x-ray absorption spectroscopy that yields both elemental and chemical sensitivity. The strong resonance enhancement of the scattering contrast offers large scattering signal for thin organic films with only tens of nanometers thick. The enhanced scattering and tunable sensitivity for organic materials can be achieved without any chemical modifications. Various scattering geometries including specular reflectivity, transmission, and grazing incidence with soft x-ray scattering make it a great complimentary tool for the study of soft material thin films. By taking advantage the unique features including elemental/chemical sensitivity, mesoscale probing size, large coherence length, and molecular orientation sensitivity with the polarization of the beam of photons, an inherent characteristic of synchrotron sources, soft x-ray scattering provides yet another key to unlock structure-property relationships that will lead to better materials. A dedicated soft x-rays scattering instrument optimized for soft materials has been constructed at Beamline 11.0.1.2 at the ALS. Some recent results on organic PV, block copolymer thin films will be presented. [Preview Abstract] |
|
V1.00263: Self-assembly of ABC miktoarm star peptides and kinetic evolution of the supramolecular morphology Yi-An Lin, Yu-Chuan Ou, Andrew Cheetham, Honggang Cui Amphiphilic peptides are versatile building blocks to engineer well-defined nanostructures. A great deal of work has shown the use of peptides to construct structures such as micelles, nanofibers, nanoribbons, or nanotubes through the rational design of peptide primary sequences. Despite amphiphilic peptides undergoing rapid self-assembly to form thermodynamically stable micellar structures, the resulting assembled morphologies are often found to slowly evolve over time. Here we report our rational design of an ABC miktoarm star peptide which comprises three immiscible domains: 1) a $\beta $-sheet adopting peptide segment with overall hydrophilicity 2) a hydrophobic hydrocarbon and 3) a hydrophobic and lipophobic fluorocarbon segment. In aqueous solution, this designed peptide can spontaneously associate into one-dimensional structures such as twisted-ribbons and helical ribbons. Transmission electron microscopy has been used to directly visualize the structural evolution with time from narrow structures into higher hierarchical large assemblies. [Preview Abstract] |
|
V1.00264: Photo-excited charge separation in CuPc/GaAs investigated by pump-probe second harmonic generation Heungman Park, Marlene Gutierrez, Xiaoxi Wu, Jeong Won Kim, Xiaoyang Zhu We report photo-excited charge carrier separation between copper phthalocyanine (CuPc) and p,n-GaAs (001) probed by time-resolved second harmonic generation (SHG). Electric field induced SHG measurements show that when GaAs is excited by 1.55 eV photons, charge carriers are initially separated by GaAs surface band bending, and then holes are injected into CuPc from GaAs regardless of doping type. The interfacial band alignment between CuPc and GaAs is determined by ultraviolet photoelectron spectroscopy and supports the hole injection from GaAs to CuPc. [Preview Abstract] |
|
V1.00265: ABSTRACT HAS BEEN MOVED TO N20.00007 |
|
V1.00266: Dynamic Light Scattering in Network-Forming Oxide Melts: Ties Between Structure and Dynamics Tri Tran, Stanley Schnell, David Sidebottom We report results from a series of dynamic light scattering studies of network-forming oxide glasses obtained using photon correlation spectroscopy. These studies focus specifically on how the dynamics of these viscous melts are influenced by systematic changes in the chemical structure of the oxide network and include studies of both sodium phosphate and sodium aluminophosphate melts. The fragility, a dynamical property of the liquid near the glass transition point, is determined from these measurements and seen to decrease with increases in the average density of bridging oxygen bonds regardless of the alkali content. Moreover, this dependence of the fragility on bond density is shown to be identically reproduced in both alkali borate melts and chalcogenide glasses, provided accommodations are made for the presence of structural entities in the borate system that contribute to their intermediate range order. The universal pattern that emerges suggests a significant tie between network structure and dynamics that is consistent with predictions for a rigidity transition near an average bond number of 2.4 and within the framework of a simple two-state bond model, may be traced to a common dependence of the configurational entropy on connectivity. [Preview Abstract] |
|
V1.00267: Role of proton ordering in adsorption preference of polar molecule on ice surface Zhaoru Sun, Ding Pan, Limei Xu, Enge Wang Adsorption of polar monomers on ice surface, relevant to the physical/chemical reaction in ice clouds as well as growth of ice, remains an open issue partially due to the unusual surface characteristics with protons at the top layer of ice. Using first-principle calculations, we explore the adsorption properties of ice surface in terms of a surface proton order parameter, which characterizes the inhomogeneity of the dangling atoms on ice surface. We show that, due to an effective electric field created by dangling OH bonds and lone pairs of water molecules not only directly neighboring but also further away from the adsorbed polar molecule on the ice surface, the adsorption energy of polar monomer on ice surface exhibits large variance and a strong correlation with the proton order parameter of ice surface. Our results about the positive correlation between the inhomogeneity of ice surface and adsorption energies suggest that the physical/chemical reactions as well as the growth of ice may prefer to occur firstly on surfaces with larger proton order parameter. [Preview Abstract] |
|
V1.00268: Frequency-dependent cavity lifetime and apparent superluminality in Fabry-Perot-like interferometer Hsin-Yu Yao, Nai-Ching Chen, Tsun-Hsu Chang, Herbert G. Winful Extraordinary group delays shorter than the transit time of light propagating at c through an equal distance have been experimentally demonstrated in single-Fabry-Perot (FP) waveguide systems and cascaded-FP structures under off-resonant conditions. These ``superluminal'' phenomena are well explained by the multiple-reflection destructive interference that reduces the intracavity stored energy when operating off resonances. Excellent agreement between theory and experiment is obtained when the dispersive effects of reflective boundaries are considered. These results provide further insight into the nature of apparent superluminality in regions of allowed propagation. [Preview Abstract] |
|
V1.00269: Angular resolved photoionization of C$_{60}$ by femtosecond laser pulses Hui Li, Zhenhua Wang, Frederik Suessmann, Sergey Zherebtsov, Slawomir Skruszewicz, Josef Tiggesbaeumker, Thomas Fennel, Karl-Heinz Meiwes-Broer, C. Lewis Cocke, Matthias Kling Neutral C$_{60}$ molecules are ionized by intense femtosecond laser pulses around the wavelength of 800 nm with pulse durations 4 fs and 30 fs. We measure photoelectrons utilizing velocity-map imaging (VMI) and analyze the photoelectron angular distributions. For particular photoelectron energies, these distributions might reflect the excitation and ionization of superatomic molecular orbitals (SAMOs) which have been theoretically predicted and only recently experimentally observed. SAMOs arise from the hollow core spherical structures of the C$_{60}$ molecules and differ from Rydberg states of C$_{60}$ by their potential to exhibit electron density within the C$_{60}$ cage. We have recorded the carrier envelope phase (CEP) dependence of the electron emission for 4 fs pulses using single shot CEP-tagging. The CEP-dependent asymmetry in the electron emission is observed to strongly depend on the laser polarization. Furthermore, the amplitudes and phases of the CEP-dependent electron emission are analyzed and show that thermal electron emission can be avoided enabling a more direct comparison to theory. [Preview Abstract] |
|
V1.00270: Violation of Cauchy-Schwarz inequalities by spontaneous Hawking radiation in resonant boson structures Fernando Sols, Juan R.M. de Nova, Ivar Zapata The violation of a classical Cauchy-Schwarz (CS) inequality is identified as an unequivocal signature of spontaneous Hawking radiation in sonic black holes. This violation can be particularly large near the peaks in the radiation spectrum emitted from a resonant boson structure forming a sonic horizon. As a function of the frequency-dependent Hawking radiation intensity, we analyze the degree of CS violation and the maximum violation temperature for a double barrier structure separating two regions of subsonic and supersonic condensate flow. We also consider the case where the resonant sonic horizon is produced by a space-dependent contact interaction. In some cases, CS violation can be observed by direct atom counting in a time-of-flight experiment. We show that near the conventional zero-frequency radiation peak, the decisive CS violation cannot occur. [Preview Abstract] |
|
V1.00271: Implementation of squeezing jump operators Roland Cristopher Caballar, Gentaro Watanabe, Sebastian Diehl, Harri M\"akel\"a We present a method to construct phase andnumber squeezed states using dissipation. Our method makes use of a gas of ultracold bosonicatoms trapped in a narrow double well embedded in a wide harmonic oscillator, with the atoms Raman coupled to the first two energyeigenstates of the harmonic oscillator. The whole system is then immersed in a background BEC to allow for dissipation from the harmonicoscillator states back to the double narrow wellstates. [Preview Abstract] |
|
V1.00272: A study on the magnetic and dielectric behavior of nanostructured YCrO$_{3}$/Al$_{2}$O$_{3}$ composite ceramics A. Duran, H. Tiznado, J.M. Romo-Herrera, E. Verdin, J. Siqueiros, R. Escudero Ferroelectric core-shell particles are promising architectures as functional bulk composites for potential use as dielectric resonators, supercapacitors, or multiferroic based devices. The core-shell architecture in ferroelectrics acts as barrier layer localizing electronic and ionic space charges, increasing thus the capacitance density. In bulk multiferroics, the barrier layer improves the grain boundary interface and leads to increased functionality, that is, higher charge storage and lower dielectric losses. In YCrO$_{3}$, large dielectric losses and changes in the activation energy have shown to be very dependent on the synthesis route as well as in the size, and chemical state of the starting grains. Increase of the conductivity and dielectric losses are associated to loose charge leaking out through the grain boundaries. Here we added an alumina shell-layer of 5, 30 or 90 nm to cover the YCrO$_{3}$ grains, using an atomic layer deposition (ALD) technique, followed by a sintering step to produce a multiferroic capacitor. The powder samples were characterized by XRD, XPS, SEM and TEM. Also, the magnetic and dielectric properties were evaluated and compared to bulk nanostructured ceramics of the same composition, but without the alumina shell. [Preview Abstract] |
|
V1.00273: Quasiparticle Dynamics in Reshaped Helical Dirac Cone of Topological Insulators Dong Qian, Miao Lin, Jinfeng Jia, Zhengfei Wang, Feng Liu Topological insulators (TIs) and graphene present two unique classes of materials which are characterized by spin polarized (helical) and non-polarized Dirac-cone band structures, respectively. The importance of many-body interactions that renormalize the linear bands near Dirac point in graphene has been well recognized and attracted much recent attention. However, renormalization of the helical Dirac point has not been observed in TIs. Here, we report the experimental observation of the renormalized quasiparticle spectrum with a skewed Dirac cone in a single Bi bilayer grown on Bi2Te3 substrate, from angle-resolved photoemission spectroscopy. First-principles band calculations indicate that the quasi-particle spectra are likely associated with the hybridization between the extrinsic substrate-induced Dirac states of Bi bilayer and the intrinsic surface Dirac states of Bi2Te3 film at close energy proximity. Without such hybridization, only single-particle Dirac spectra are observed in a single Bi bilayer grown on Bi2Se3, where the extrinsic Dirac states Bi bilayer and the intrinsic Dirac states of Bi2Se3 are well separated in energy. The possible origins of many-body interactions are discussed. Our findings provide a means to manipulate topological surface states. [Preview Abstract] |
|
V1.00274: Converting an engine driven by non-uniform temperature to one driven by load Mulugeta Bekele, Tolasa Adugna, Tatek Yergou Consider a Brownian particle moving in a symmetric ratchet potential (barrier height U$_{\mathrm{0}}$, period L) and in an equally periodic alternate hot (T$_{\mathrm{h}})$ and cold (T$_{\mathrm{c}})$ temperature background along the same space coordinate (case I). Under steady state condition, the particle will attain a constant average velocity. On the other hand, if we replace the non-uniform temperature background by a uniform temperature (T$_{\mathrm{c}})$ with a load (f) keeping the same ratchet potential (case II), the particle will attain a constant average velocity down the load at steady state. In this work, we evaluate the amount of load for case II that gives identical value of average velocity to that of the non-uniform temperature background of case I. We, in general, explore the condition under which both cases have equivalent particle velocities by varying the barrier height of the ratchet. [Preview Abstract] |
|
V1.00275: Effect of chemical and heat treatment on the superconducting properties of niobium used in superconducting radiofrequency cavity fabrication Pashupati Dhakal, Gianluigi Ciovati, Ganapati Rao Myneni Niobium is the material of choice for the fabrication of the superconducting radiofrequency (SRF) cavities used in particle accelerator. In the last four decades, much work has been done to push the performance of SRF cavity to its theoretical limits of the accelerating gradient and high quality factor. One of the issues towards achieving those limits is the high residual loss and occurrence of a sharp increase of the RF losses (decrease in quality factor) when the peak magnetic field reaches about 100 mT, consequently limiting the operational accelerating gradient of SRF cavities. We present the result on the effect of the surface and heat treatment on ac and dc superconducting properties to explore the limiting factors of the SRF cavity performance. [Preview Abstract] |
|
V1.00276: Novel spin-liquid behaviour in some Ir-based oxide systems A.V. Mahajan, T. Dey, P. Khuntia, M. Baenitz, B. Koteswararao, F.C. Chou, A.A. Omrani, H.M. Ronnow The 5d-transition metal based oxide systems are of current interest due to the prominence of spin-orbit coupling driving them to a Mott insulating state in spite of a small Coulomb repulsion energy U. We have recently investigated Ba3IrTi2O9 and Ba3YIr2O9 systems (with hexagonal arrangement of Ir) using x-ray diffraction, magnetization, heat capacity, and NMR. With a power-law temperature dependence of the low-T magnetic heat capacity, we find evidence of spin-liquid behavior in the former. Whereas the latter is magnetically long-range ordered below 4 K, it transforms to a cubic structure when reacted at 1273 K under a pressure of 8GPa. The high-pressure (HP) prepared sample, though with semiconductor-like resistivity, has (in addition to the phonon term) a T-linear heat capacity term with $\gamma$ = 10 mJ/mol K$^2$ and a T-linear $^{89}$Y NMR spin-lattice relaxation rate. We conclude that the HP phase exhibits spin-liquid behavior. [Preview Abstract] |
|
V1.00277: Effect of Surface Morphology on Adhesion of Graphene Changgu Lee, Dae-Hyun Cho, Jin-Seon Kim, Taiyu Jin, Jinyoung Kang, Renlong Liu, Youngchan Kim, Lei Wang, Gwan-Hyoung Lee, James Hone The friction of graphene on various substrates, such as SiO2, h-BN, graphite, and mica, was investigated to characterize the adhesion level between graphene and the underlying surface. The friction of graphene on SiO2 decreased with increasing thickness and converged around the penta-layers due to incomplete contact between the two surfaces. However, the friction of graphene on an atomically flat substrate, such as h-BN and graphite, was low and comparable to that of bulk-like graphene. In contrast, the friction of graphene folded onto graphite was indistinguishable with that of mono-layer graphene on SiO2 despite the ultra-smoothness of the graphite. The characterization of the graphene's roughness before and after folding showed that the corrugation of graphene induced by SiO2 morphology was preserved even after it was folded onto an atomically flat substrate. In addition, graphene deposited on mica, when folded, preserved the same corrugation level as before the folding event. We found that graphene, once exfoliated from the bulk crystal, tends to maintain its corrugation level even after it is folded onto an atomically flat substrate and that ultraflatness in both graphene and the substrate is required to achieve the intimate contact necessary for strong adhesion. [Preview Abstract] |
|
V1.00278: Coupling the valley degree of freedom to antiferromagnetic order Xiao Li, Ting Cao, Qian Niu, Junren Shi, Ji Feng Conventional electronics are based invariably on the intrinsic degrees of freedom of an electron, namely, its charge and spin. The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley as a new electronic degree of freedom has received considerable attention in recent years. In our paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by coupling the valley degree of freedom to antiferromagnetic order, there is an emergent electronic degree of freedom characterized by the product of spin and valley indices, which leads to spin-valley dependent optical selection rule and Berry curvature-induced topological quantum transport. These properties will enable optical polarization in the spin-valley space, and electrical detection/manipulation through the induced spin, valley and charge fluxes. The domain walls of an antiferromagnetic honeycomb lattice harbors valley-protected edge states that support spin-dependent transport. Finally, we employ first principles calculations to show that the proposed optoelectronic properties can be realized in antiferromagnetic manganese chalcogenophosphates (MnPX$_{\mathrm{3}}$, X $=$ S, Se) in monolayer form. [Preview Abstract] |
|
V1.00279: Probing the transport properties of graphene nano\-structures produced by local anodic oxidation Nils Freitag, Aviral Vaid, Marcus Liebmann, Felix Jekat, Theresa Hecking, Alexander Nent, Markus Morgenstern Graphene flakes exfoliated on 300 nm SiO$_2$/Si and contacted by Indium soldering are modified by local anodic oxidation in an atomic force microscope (AFM). By varying voltage, tip velocity and contact pressure, we produced either cuts or areas appearing as elevations in AFM. The width of the cuts and elevations ranged down to 15 nm and 35 nm respectively. However, the cuts are mostly surrounded by additional elevations. The elevations are insulating at room temperature with an areal resistance of several T$\Omega$ and exhibit a D and a 2D peak in Raman spectroscopy. Transport studies on an Aharanov-Bohm ring with a diameter of 600 nm showed magnetooscillations with a visibility of 0.2\% at 300 mK and a strong peak around 0 T attributed to weak localization within the ring. Transport measurements on a Quantum Dot structure with a diameter of 60 nm and several side gates showed several Coulomb diamonds, however, with addition energies not compatible with the structured dot area. Nevertheless, the plunger gate was six times more effective than the back gate and charge rearrangements were seldom observed. [Preview Abstract] |
|
V1.00280: Fabrication of sub-20 nm metal lines on Si substrates Yukta P. Timalsina, Zonghuan Lu, Liang Chen, Kim Lewis, Toh-Ming Lu As line width decreases below 15 nm, the diffusion barriers used in copper (Cu) technology in high performance integrated circuits significantly increase the overall resistivity of interconnects. In this work, we argue that the performance of pure W and Mo lines with line widths smaller than 15 nm could be better than that of Cu lines with barriers. We, herein, present a process of creating Cu, W and Mo metal nanolines on Si substrates using the combination of e-beam lithography (SUPRA 55 Scanning electron microscopy), oblique angle deposition, and lift-off techniques. The integrity of the sub-15 nm nanolines, including the line edge roughness, will be quantified. We shall also report our attempts to measure the resistivity of these nanolines using four point probe techniques. The relative contributions of phonon scattering versus surface scattering will be discussed. The effect of line edge roughness to the overall resistivity will also be presented. [Preview Abstract] |
|
V1.00281: Fabrication of canonical nanoporous templates by variational anodic oxidation of aluminum Ataur Chowdhury, Patrick Wallace The interesting effects of quantum confinement critically depend on the shape and size of the nanocrystals. Preliminary results of an experimental study of production of templates with conical profiles are presented here. These templates will be ideal for fabrication of nanocrytals with the same profile. Templates were fabricated in aluminum with the anodic oxidation process by carefully controlling the anodization parameters to control the shape of the resulting templates. Different combinations of theses parameters such as electrolyte, pH of the solution, applied voltage, and current density were studied to ascertain the right condition of growth for conically porous templates. The most dominant parameter was the applied voltage and the voltage was continuously changed slowly during the process of growth. Attempt was made to control the pore diameter to a size less than 20 nm with an aspect ratio of about 1.0. Structural and morphological studies were done with AFM and SEM. The details of the results will be presented. [Preview Abstract] |
|
V1.00282: Design study of the Low Energy Beam Transport system at RISP Jungbae Bahng, Eunsan Kim, Yonghwan Kim, In-Seok Hong We present the design status of LEBT for the RISP that consists of two 90 degree dipoles, a multi-harmonic buncher, pair solenoids, electrostatic quadrupoles and a high voltage platform. After ECR-IS with an energy of 10 keV/u, heavy-ion beams are selected by achromatic bending systems and then be bunched in the LEBT. A multi-harmonic buncher is used to achieve a small longitudinal emittance in the RFQ. We show the results on the optics design by using the TRANSPORT code and the beam tracking of two-charge beams by using the code IMPACT. We present the results and issues on beam dynamics simulaitons in the designed LEBT system. [Preview Abstract] |
|
V1.00283: Accelerating Molecular Dynamics Simulation on the Many Integrated Core (MIC) Platform Hongsuk Yi, Hogyun Jeong, Seungmin Lee Graphics processing units and Intel Many Integrated Core (MIC) architectures have emerged as alternative computational strategy in computational physics that can significantly speed up high performance computing algorithms. In this paper, we present early experiences on the MIC platform, focusing on porting of molecular dynamics (MD) kernels with the Tersoff potentials for carbon covalent crystals. In particular, we implement our MD code on heterogeneous computing platform consisting of Intel Xeon processors and Intel MIC architecture co-processors, using offload and OpenMP. The fully optimized MIC version achieves about 8 times speedup over the original CPU version. Furthermore, explicit vectorization on the MIC with 512-bit wide vector registers is found to be critical to achieving good performance of this algorithm in this type environments. [Preview Abstract] |
|
V1.00284: Efficient quantification of experimental evidence against local realism Yanbao Zhang, Scott Glancy, Emanuel Knill It is highly desirable to have reliable experimental demonstrations of violations of Bell inequalities for rejecting local realism. A potential problem is that due to statistical fluctuations, a finite set of data points generated by a local realistic model can violate a Bell inequality. In order to statistically quantify the evidence against local realism in an experiment, one needs to compute an upper bound of the probability according to local realism of a violation at least as high as that observed. Such bounds not only help to reliably demonstrate violations of local realism, but also help to prove the security of quantum key distribution or certify the generation of genuine randomness. We describe an efficient protocol for computing such a bound from any set of Bell inequalities for any number of parties, measurement settings, or outcomes. The bound depends on the choice and number of Bell inequalities, and generally, more inequalities make the bound asymptotically tighter. We find that even trivial Bell inequalities such as no-signaling conditions can improve the tightness of the bound. In addition, this protocol can be adapted to any test with linear witnesses, such as tests for entanglement or system dimensionality, without a full analysis of the relevant probability space. [Preview Abstract] |
|
V1.00285: Low-temperature metallic liquid hydrogen: an ab-initio path-integral molecular dynamics perspective Ji Chen, Xin-Zheng Li, Qianfan Zhang, Matthew Probert, Chris Pickard, Richard Needs, Angelos Michaelides, Enge Wang Experiments and computer simulations have shown that the melting temperature of solid hydrogen drops with pressure above about 65 GPa, suggesting that a low temperature liquid state might exist. It has also been suggested that this liquid state might be non-molecular and metallic, although evidence for such behaviour is lacking. Using a combination of ab initio path-integral molecular dynamics and the two-phase methods, we have simulated the melting of solid hydrogen under finite temperatures. We found an atomic solid phase from 500 to 800 GPa which melts at \textless\ 200 K. Beyond this and up to pressures of 1,200 GPa a metallic atomic liquid is stable at temperatures as low as 50 K. The quantum motion of the protons is critical to the low melting temperature in this system as ab initio simulations with classical nuclei lead to a considerably higher melting temperature of $\sim$300 K across the entire pressure range considered. [Preview Abstract] |
|
V1.00286: Modeling brittle material failure under high velocity impact conditions: From experiments to simulations Andrew Tonge, K.T. Ramesh Brittle materials have a deviatoric strength that is highly dependent on the applied pressure. To successfully model impact events involving brittle materials it is important to capture both the hydrostatic response, which is dominated by the equation of state, and the deviatoric response witch is dominated by the activation of microcracks within the material. The behavior of microcracks within the material is strongly affected by the applied pressure and gives rise to a material strength that is rate, size, and pressure dependent. In this work we present a material model that is based on an experimentally motivated micromechanics damage growth model coupled with a Mie-Gruneisen equation of state. We use this material model to simulate quarter inch glass spheres impacting a basalt cube at 2.2 km/s. [Preview Abstract] |
|
V1.00287: Ionic Transport and Structural Characterization of the Lithium-Rich Anti-Perovskite Li3OCl John Howard, Luke Daemen, Monika Hartl, Jerzy Chlistunoff, Yusheng Zhao We will discuss the structural and electrochemical characterization of the newly synthesized lithium-rich anti-perovskite, Li$_3$OCl. The crystal structure of this compound was solved using x-ray diffraction techniques, and the electronic and ionic conductivities were measured using electrochemical impedance spectroscopy. This material has an ionic conductivity ranging approximately from $10^{-4}$ S/cm to $10^{-1}$ S/cm over the temperature range $25^{\circ}$C to $270^{\circ}$C (room temperature to just below the melting point). The high ionic conductivity of this lithium-rich electrolyte demonstates strong promise that this material is an ideal candidate for solid state battery applications. [Preview Abstract] |
|
V1.00288: Free-standing Conductive Fe$_{3}$O$_{4}$/Graphene/CNT Film As Anodes for Lithium-Ion Batteries Yue Cai, Yingwen Cheng, Songtao Lu, Hongbo Zhang, C.V. Varanasi, Jie Liu Fe3O4 is known as a material for lithium-ion battery anodes due to its high theoretical specific capacity. But it has limitations, such as low conductivity and poor cyclic performance etc. To address these problems, free-standing Fe3O4/Graphene/Carbon nanotube(CNT) films were prepared via hydrothermal reaction methods. The synergistic effect of graphene and CNTs provide a flexible matrix for Fe3O4. A series of experiments were performed to determine important processing factors such as carbon ratio and annealing treatments, which influenced the overall LIB performances. Currently the best film had a sheet resistance of 23 ohm/sq and a BET surface area of 132 m2/g. In addition, the lightweight films were directly tested as lithium-ion battery anodes without using a current collector or a binder, eliminating unnecessary weight in the overall devices. This metal oxide loaded carbon film had both excellent conductivity and strong mechanical strengths. The discharge capacity was found to reach 880 mAh/g at 200 mA/g current density and 580 mA/g at 400 mA/g. The rate capability tests (from 200 mA/g up to 1200 mA/g) also indicated that the lab prepared Fe3O4 loaded films have much better performance as compared to the samples made by using commercial Fe3O4. [Preview Abstract] |
|
V1.00289: A Three-Dimensional reduced Graphene Oxide/Nickel Oxide Composite in a Thin, Porous Carbon Framework to serve as a Supercapacitor Electrode Gyeonghee Lee, C.V. Varanasi, Jie Liu In recent years, environmental problems and the depletion of fossil fuels have encouraged intense research to discover ways to store energy such as supercapacitors. NiO is considered as a highly promising candidate for electrodes in supercapacitors due to its high theoretical capacitance, superior stability in alkaline electrolytes and low cost. However, the poor conductivity of NiO limited its capacitance to low value. In this work, NiO coated reduced graphene oxide (rGO) network in a conductive carbon matrix was synthesized. A porous carbon paper (CP) was utilized as a conductive framework on which initially Ni(OH)$_{\mathrm{2}}$ was vertically grown via solvothermal reaction. Graphene oxide (GO) hydrogel was formed on the Ni(OH)$_{\mathrm{2}}$ coated carbon paper through the dissolution of Ni(OH)$_{\mathrm{2}}$. Controlling the uniformity of Ni(OH)$_{\mathrm{2}}$ coating on the carbon paper was a key factor to homogeneous loading GO onto the carbon paper. Ni(OH)$_{\mathrm{2}}$ was loaded again on GO hydrogel formed on the carbon paper (CP-GO-Ni(OH)$_{\mathrm{2}})$ as NiO precursor. After annealing, CP-rGO-NiO composite exhibited a high specific capacitance and excellent cycle stability compared to the electrochemical performance of rGO-NiO composite connected to a carbon paper using binder. The structural and electrochemical properties of CP-rGO-NiO composite will be presented. [Preview Abstract] |
|
V1.00290: Lagrangian Approach to Study Catalytic Fluidized Bed Reactors Hossein Madi Lagrangian approach of fluidized bed reactors is a method, which simulates the movement of catalyst particles (caused by the fluidization) by changing the gas composition around them. Application of such an investigation is in the analysis of the state of catalysts and surface reactions under quasi-operando conditions. The hydrodynamics of catalyst particles within a fluidized bed reactor was studied to improve a Lagrangian approach. A fluidized bed methanation employed in the production of Synthetic Natural Gas from wood was chosen as the case study. The Lagrangian perspective was modified and improved to include different particle circulation patterns, which were investigated through this study. Experiments were designed to evaluate the concepts of the model. The results indicate that the setup is able to perform the designed experiments and a good agreement between the simulation and the experimental results were observed. It has been shown that fluidized bed reactors, as opposed to fixed beds, can be used to avoid the deactivation of the methanation catalyst due to carbon deposits. Carbon deposition on the catalysts tested with the Lagrangian approach was investigated by temperature programmed oxidation (TPO) analysis of ex-situ catalyst samples. This investigation was done to identify the effects of particles velocity and their circulation patterns on the amount and type of deposited carbon on the catalyst surface. [Preview Abstract] |
|
V1.00291: Tangential Relations between Distorted Acute Angles vs. Original Acute Angles of a Traveling Right Triangle in Special Relativity Florentin Smarandache Let's consider a traveling right triangle $\Delta $\textit{ABC} ($\angle A=\pi /2)$, with the speed $v$, and one of its legs \textit{AB} along the motion direction on the $x-$axis. After contraction of the side $AB$ with the factor C(v), and consequently contraction of the oblique side $BC$ with the oblique-contraction factor \[ OC(v,\theta )=\sqrt {C(v)^{2}\cos^{2}\theta +\sin^{2}\theta } , \] one gets the right triangle $\Delta A'B'C'$ with the following tangential relations between distorted acute angles vs. original acute angles of the right triangle: \[ \tan B'=\frac{\tan B}{C\left( v \right)}, \] \[ \tan C'=\tan C\cdot C\left( v \right), \] where $C(v)=\sqrt {1-\frac{v^{2}}{c^{2}}}_{\, \, }$is the Lorentz contraction factor, and $c$ is the speed of light in vacuum. [Preview Abstract] |
|
V1.00292: Distinction between \textit{Clock} and \textit{Time}, and a Suggested Experiment with Different Types of Clocks in GPS Florentin Smarandache The clock is an instrument for measuring the time, instrument that may not run perfectly (accurately) under certain conditions (like, say, in strong electromagnetic field, in strong gravitational field, in extremely high or low temperature, pressure, etc.), but this does not mean that time itself runs slower or faster as Einstein's Theory of Relativity asserts. We are referring to an absolute time, i.e. time measured not with respect to ether or non-ether, but with respect to an absolute mathematical reference frame. Several types of clocks could run at a more slowly rate in a moving frame of reference than other types of clocks; it depends on the \underline {construction material} and \underline {functioning principle} of each \textbf{type of clock}. Relativists say that ``gravity slows time''. This is incorrect, since actually \textit{gravity slows today's types of clocks}. And one type of clock is slowed more or less than another type of clock. Not only gravity but other (electric, magnetic, etc.) fields or various medium composition elements or structures may slow or accelerate clocks that are in that medium. The clocks used today in the satellites for the GPS necessitate a correction with respect to the Earth clocks. But in the future, when new types of clocks will be built based on different construction material and functioning principle, the correction of the GPS clocks would be different. In order to make the distinction between ``clock'' and ``time'', we suggest a \textbf{Experiment {\#} 1} with different types of clocks for the GPS clocks, in order to prove that the resulted dilation and contraction factors are different from those obtained with today's cesium atomic clock. [Preview Abstract] |
|
V1.00293: A Study of Energetics and Molecular Dynamic Simulations of Ag Nanoclusters Melihat Madran, Mine Konuk, Sondan Durukanoglu We present results of molecular static and molecular dynamic calculations for the energetics of adatom and small cluster dynamics on the facets of truncated octahedral silver nano-particles. To identify the governing diffusion mechanisms during growth of the cluster the diffusion barriers on the various facets are calculated using nudged elastic band method based on the potentials extracted from embedded atom method. We also performed calculations to examine the possible influence of geometry on the diffusion dynamics of a single atom or a cluster on the facets of the nano-particles. Our growth simulations show that the energy barriers for diffusions between the different facets of truncated octahedral of silver remarkably reduced in the presence of the small aggregates on the facets. Using the results of energetic calculations and molecular dynamic simulations we further discuss the possible mechanisms for structural transition in a growth on truncated octahedral silver nano-particles. This work is supported by TUBITAK under Grand no. TBAG-109T105. [Preview Abstract] |
|
V1.00294: Free Energy Landscapes of DNA Stretching Using Crooks Fluctuation Theorem Eric Frey, Ching-Hwa Kiang Free energy landscapes can be reconstructed from nonequilibrium, single-molecule manipulation by using nonequilibrium work theorems. Previous studies have reconstructed landscapes of the unfolding of RNA, DNA hairpins, and proteins. Such landscapes have thus far exhibited one single pathway, or the free energy is that of the combined molecule-plus-force-probe system used in the experiments. Here we reconstruct a multiple-pathway, branched free energy landscape of poly(dA), as a function of molecular end-to-end extension, from nonequilibrium single-molecule measurements. We show that the Crooks fluctuation theorem can be used to reconstruct the landscape of poly(dA) stretching. [Preview Abstract] |
|
V1.00295: Simulations of adsorption of CO2 and CH4 in MOFs: effect of the size and charge distribution on the selectivity Sidi Maiga, Silvina Gatica Using the method of Grand Canonical Monte Carlo we have computed the adsorption of CO2 and CH4 in MOFs with a periodic cubic structure. We used a model of the MOF that allows systematic variations in the charge distribution, size and LJ parameters. We estimated the selectivity of CO2 over CH4 for different temperatures in MOFs with various sizes and charge distributions. The results show that inserting dipoles at the corners of the MOF's unit cell would increase the selectivity of CO2; on the other hand adding quadrupoles to the structure is ineffective. The size of the cell strongly affects the adsorption of CO2 and selectivity: compressing the cell in only 10{\%} significantly increases the selectivity; expanding the cell by 20{\%} reduces it. Regarding thermal effects, we estimated that the selectivity drops from 250 to 2 when the temperature rises from 140K to 300K. Although this model is inspired by the IRMOF-1, which has a cubic unit cell, it can be adapted to represent other MOFs with noncubic structures by modifying the geometry accordingly. This work implies that MOFs suit gas separation. [Preview Abstract] |
|
V1.00296: Label-free electrical detection of ovarian cancer biomarker CA-125 with a novel nanoscale coaxial array Michelle Archibald, Binod Rizal, Dong Cai, Timothy Connolly, Michael J. Burns, Michael J. Naughton, Thomas C. Chiles Technologies to detect early stage cancer would provide significant benefit to cancer disease patients. Clinical measurement of biomarkers offers the promise of a noninvasive and cost effective screening for early stage detection. We have developed a novel 3-dimensional nanocavity array for the detection of human cancer biomarkers. This all-electronic diagnostic sensor is based on a nanoscale coaxial array architecture that enables molecular-level detection. Each individual sensor in the array is a vertically-oriented coaxial capacitor, whose capacitance is measurably changed when target molecules enter the coax annulus. The coaxial array facilitates electrical-based detection in response to antibody or molecular imprint based recognition of a specific cancer biomarker, thereby providing a label-free, non-optical measurement. Here, we describe this nanoscale 3D architecture and its application to the detection of the ovarian cancer biomarker CA-125. We report our efforts on the development of molecular detection of CA-125 based on antibody-functionalized nanocoax arrays as well as molecular imprints. The results demonstrate the feasibility of using these arrays as ultrasensitive devices to detect a wide range of molecular targets, including disease biomarkers. [Preview Abstract] |
|
V1.00297: Inductional Effects in a Halbach Magnet Motion Above Distributed Inductance Yves Tchatchoua, Ary Conrow, Dong Kim, Daniel Morgan, Walerian Majewski, Zaeema Zafar We experimented with attempts to levitate a linear (bar) Halbach array of five 1" Nd magnets above a linear inductive track. Next, in order to achieve a control over the relative velocity, we designed a different experiment. In it a large wheel with circumferentially positioned along its rim inducting coils rotates, while the magnet is suspended directly above the rim of the wheel on a force sensor. Faraday’s Law with the Lenz's Rule is responsible for the lifting and drag forces on the magnet; the horizontal drag force is measured by another force sensor. Approximating the magnet's linear relative motion over inductors with a motion along a large circle, we may use formulas derived earlier in the literature for linear inductive levitation. We measured lift and drag forces as functions of relative velocity of the Halbach magnet and the inductive ``track,'' in an approximate agreement with the existing theory. We then vary the inductance and shape of the inductive elements to find the most beneficial choice for the lift/drag ratio at the lowest relative speed. [Preview Abstract] |
|
V1.00298: Physical Models of a Toroidal Dipole Duke Forsyth, Kiarash Akhlaghi, Martin Azir, Vikram Sarkhel, Walerian Majewski We are investigating two models of the third (after well-known electric and magnetic dipoles) elementary dipole - the toroidal dipole. Its electric model is a toroidal coil connected to a DC or AC voltage, its magnetic version is a circumferentially magnetized ring of neodymium, at rest or rotating. DC electric and magnetic toroids produce only inner magnetic field, and interact directly with a curl of the external magnetic field, that is - with a conductive current density or with a displacement current. Toroidal dipole moment was measured in interaction with the external current and compared with a calculated theoretical value. Rotating magnetic toroid or the AC electric toroid should each act as an electric dipole antenna and produce electric dipole radiation. We are attempting to detect and measure their near-zone electromagnetic fields, as well as an integrated value of the external magnetic vector potential A. [Preview Abstract] |
|
V1.00299: Experiments on Inductive Magnetic Levitation with a Circular Halbach Array Ian Bean, Doug Goncz, Austin Raymer, Jason Specht, Ricardo Zalles, Walerian Majewski Using a ring Halbach array, we are investigating a repulsive levitating force and a drag force acting on the magnet from a ring of inductors rotating below the magnet. After measuring induced currents, voltages and magnetic fields in the individual inductors (in the form of short solenoids), we investigated the dependence of lift/drag forces on the speed of relative rotation. The ratio of lift to drag increases with the angular velocity, as expected from a related theory of the induction effects in a linear motion. We are experimenting with the shape and density of inductors, and their material, in an attempt to maximize the lift at a minimal velocity of rotation. Eventually this design could have applications as frictionless bearings or as frictionless gear in a wide range of systems, especially in machinery that cannot be easily accessed. [Preview Abstract] |
|
V1.00300: An Experimental Study of a Nonlinear Phased Array Interacting with Solid Media Paul Anzel, Carly Donahue, Chiara Daraio We present results in our development of a nonlinear phased array capable of focusing highly compact waves in solid media. The phased array consists of parallel chains of spherical particles in contact. When the chains are excited by an impulse, the nonlinear Hertzian force between elastic spheres allows for the formation and propagation of a solitary wave: a localized collective motion of the spheres, which maintains its shape over a long length of travel and carries a significant amount of mechanical energy. Unlike in linear media, the speed of these solitary waves can be tuned by applying a compressive force to the chain. The different pre-strain applied to the chains induces a signal delay in the system. When the phased array is placed adjacent to a medium of interest, it can focus the transmitted pulses of energy to a chosen location in the medium, creating a ``sound bullet''. Here, we present results in system repeatability and we investigate the limitations of the system to off axis focusing. We compare experimental results to numerical values and analytical predictions. [Preview Abstract] |
|
V1.00301: Long Working Distance Fluorescence Detection and Lifetime Imaging through Stimulated Emission Fu-Jen Kao, Po-Yen Lin Stimulated emission is a newly developed modality that has found increasing applications in advanced optical microscopy. Its utilization offers a variety of advantages over spontaneous one, including stimulated emission depletion microscopy (STED) for sub-diffraction limited resolution and stimulated emission detection for dark fluorophores. In this presentation, we are demonstrating the unique aspects of spatial coherence as a result of stimulated emission, which is applied for long working distance fluorescence detection and lifetime imaging. When compared spontaneous emission, stimulated emission based detection does not require high numerical aperture optics to collect signal efficiently. The characterization of fluorescence lifetime and anisotropy measurement through stimulated emission are investigated and summarized succinctly in this presentation. [Preview Abstract] |
|
V1.00302: Suspended MoS2 devices Taiyu Jin, Jinyoung Kang, Renlong Liu, Youngchan Kim, Changgu Lee Single or a few layer MoS2 sheets have been reported to have high electric mobility and current on/off ratio comparable to those of silicon due to its semiconductor properties with bandgap of 1.3 $\sim$ 1.9eV. However, its extremely high surface to volume ratio and low thickness prohibits it from reproducing its electronic properties on SiO2 substrates possibly because of charge scattering by surface charges and phonons. In order to investigate these surface effects, we fabricated MoS2 devices suspended from the SiO2 and characterized their electronic transport properties. We exfoliated single or a few layer MoS2 on SiO2 substrates first, and fabricated field effect transistors using e-beam lithography. After that, we suspended MoS2 sheets by etching SiO2 with hydrofluoric acid. We measured mobility and current on/off ratio before and after the etching process. We found that mobility of MoS2 devices increased by factor of 5-10 after etching for all devices. However, on/off ratio did not show significant variation. Our measurements suggest that atomically thin MoS2 devices are significantly affected by substrate surface and environment. [Preview Abstract] |
|
V1.00303: Scalable patterning of one-dimensional dangling bond chains on hydrogenated Si(001) surfaces Francois Bianco, Maria Longobardi, David R. Bowler, James H.G. Owen, Christoph Renner Silicon dangling bonds exposed on monohydride silicon (001) surface are highly reactive, and enable site selective absorption of atoms and single molecules into specific patterns designed into Si(001):H surfaces through the controlled removal of hydrogen atoms. Current implementations of such hydrogen lithography rely on painstaking removal of hydrogen atoms using the tip of a scanning probe microscope. Here, we present a scalable thermal process that yields very long chains of dimer wide silicon dangling bonds to self-assemble atoms and molecules into one-dimensional structures of unprecedented length on Si(001):H. [Preview Abstract] |
|
V1.00304: Diffusion with traps as the mechanism behind the retentivity relaxation of the resistive state on bipolar RRAM devices Alejandro Schulman, Marcelo J. Rozenberg, Carlos Acha The relaxation of the remnant resistance state obtained immediately after the electric-pulse switching process on metal/complex oxide interfaces [(Au, Pt) / (YBCO, LSMO)] has been studied. We have found that resistance relaxes following a stretched exponential law, with a temperature and applied switching power independent exponent. More interesting and unlike ordinary thermal diffusion processes, we observe that the characteristic relaxation time increases with increasing temperature and applied power. This anomalous dependence of the characteristic time gave us the opportunity to find an interesting physic process related to the oxygen diffusion on complex oxides, like superconducting cuprates or colossal magnetoresistant manganites: We argue that the observed behavior, common for both complex oxide interfaces, points to a generic phenomenon that can be understood as due to the diffusion of oxygen ions (or oxygen vacancies) moving on a 2D surface (grain boundaries) with a temperature dependent density of trapping centers. [Preview Abstract] |
|
V1.00305: Monte Carlo simulation of highly oxidized oligopyrroles in condensed phases Weixiao Ji, Clifford Hall, Estela Blaisten-Barojas We present a new classical model potential for the simulation of oxidized oligopyrroles. The novel potential treats the monomers as rigid bodies interacting through covalent, bending, torsion, dipole-dipole, anti-coiling, excluded volume and coulomb interactions. The potential contains 24 parameters fitted on a database of energy points calculated at the density functional theory quantum approach. Studies include structural and mechanical properties of condensed phase systems composed of 1188 pyrrole oligomers with 12 monomers each and 4752 electronegative atoms yielding a 33{\%} dopant concentration. The mechanical equilibrium density is determined by isothermal-isobaric Monte-Carlo. The equilibrium configurations at various temperatures are studied in the canonical ensemble and our Adaptive Tempering Monte Carlo (ATMC), a multi-canonical ensemble method, finds the global minimum of the energy. Binding energy, end-to-end distance, radius of gyration, vector and orientation order parameters, and pair correlation functions are reported at 300K and 1000K.A new computational algorithm in CUDA allows a significant computer acceleration using GPUs. With this novel implementation we obtain speedup of a 45-factor faster than CPU at sufficiently large system sizes. [Preview Abstract] |
|
V1.00306: Effect of the Pattern Curvature on Thin Film Stability Guiduk Yu, June Huh, Kyusoon Shin, Kookheon Char By taking advantage of mesoscopically concave and convex patterns, we investigated the effect of pattern curvature on the stabilities of polystyrene (PS) films. The PS thin films were found to rupture on the patterns driven by the Laplace pressure. The dewetting of PS films was found to start from the peaks of each pattern, followed by the underfills in the valleys. In spite of the similar rupture behavior at the early stage, the dewetting morphologies at the later stage exhibited the pattern curvature dependence. The films placed on the substrates with concave patterns mostly wetted the substrates whereas PS films transferred to the substrates with convex patterns accompanied the micron-scale ruptures by exposing most area of the patterns to air. By scratch experiments, the film rupture was analogously observed to be localized in the vicinity of scratches on the concave patterns while propagating in much wider area in the case of the convex patterns. The dissimilar behavior based on the pattern curvature was found to originate from the opposite gradient of each pattern, associated with the local contact instability of dewetted films. [Preview Abstract] |
|
V1.00307: Inducing extended line defects in graphene by linear adsorption of C and N atoms Yu Li, RuiQin Zhang, Zijing Lin, Michel A. Van Hove We propose a possible approach for controlled formation of various 585 (containing pentagonal and octagonal carbon rings) extended line defects (ELDs) by linear adsorption of various kinds of atoms (C, N, B, O) on a graphene substrate, based upon density functional theory and molecular-dynamics (MD) simulations. We find out that the C and N atoms spontaneously transform to 585 ELDs while other elements find specific stable configurations. To confirm the feasibility of forming the ELD from line adsorption, investigation of the critical transformation conditions of the 585 ELD is involved based upon various adsorption models and adsorption densities. [Preview Abstract] |
|
V1.00308: Fast-Shock Ignition: A New Concept to Inertial Confinement Fusion Seyed Abolfazl Ghasemi, Amir Hossein Farahbod A new concept for inertial confinement fusion called fast-shock ignition (FSI) is introduced to obtain high target gain. In the proposed model, the separation of fuel ignition into two successive steps, under the suitable conditions, reduces required ignitor energy. The main procedure in FSI concept is at first, compressing the fuel up to stagnation. Then, two high intensity short pulse laser spikes with energy and power lower than those required for shock ignition (SI) and fast ignition (FI) with a proper delay time launched at the fuel which increases the central hot-spot temperature and complete the ignition of the pre compressed fuel. The introduced semi-analytical model indicates that with fast-shock ignition, the total required energy for compression and ignition of the fuel can be slightly reduced in comparison with pure shock ignition. Furthermore, for fuel mass greater than 2mg, the target energy gain increases up to 15 percent and the contribution of fast ignitor could be decreased about 20 percent over pure fast ignition. The FSI scheme is beneficial from technological considerations for the construction of short pulse high power laser drivers. The general advantages of fast-shock ignition over pure shock ignition can be better than 1.3. [Preview Abstract] |
|
V1.00309: Excitonic probing of magnetic spin states and their temperature evolution in semiinsulating CdMnTe spin-glasses Yuriy Gnatenko, Petro Bukivskij Spin glass (SG) formation is one of the most complex and exciting problems in the condensed matter physics. In spite of the intensive theoretical and experimental investigations of SG systems, a number of issues still remain open. In particular, the relative concentrations (RCs) of ``loose'' (single) spins and various magnetic spin clusters in SGs is one of the important unanswered questions. Another problem is lack of detailed quantitative information on how these microscopic magnetic spin states (MMSSs) evolve with temperature. Here, we have investigated (MMSSs) \{``loose spins, finite superparamagnetic, ``locked'' and infinite clusters\} both above and below the freezing temperature in Cd$_{0.70}$Mn$_{0.30}$Te SG. We used the localized exciton magnetic polarons (LEMPs), which we observed in the photoluminescence spectra, as a probe of these state. This makes it possible for the first time to estimate the MMSS's RCs and to study their temperature evolution and thus to elucidate one of the most important issues in this field of research. Furthermore, the findings described here may encourage researchers for more detailed studies of freezing process in various inhomogeneous magnetic glassy systems, especially, in dilute magnetic semiconductors -- a very promising materials for spintronics. This also opens intriguing prospects for further studies of spin freezing and frozen states in these systems, especially under influence of extrinsic factors (magnetic field, pressure, ultrasound etc). [Preview Abstract] |
|
V1.00310: Nanoscintillators based on the emission of self-trapped excitons in layered PbI$_{2}$ nanoclusters Yuriy Gnatenko, Anatoli Bukivskii, Yuriy Piryatinski We studied the dynamics of excitons excited in layered semiconductor PbI$_{2}$ nanoclusters (NCLs), embedded in CdI$_{2}$ crystal matrix, using time-resolved photoluminescence (TRPL) spectroscopy. TRPL spectra reveal formation of self-trapped excitons (STEs) in nanosecond scale. The effective energy transfer from the small to the larger semiconductor NCLs, which arises from dipole-dipole intercluster interactions, takes place in sub-nanosecond scale. We demonstrate that the STEs are stable states and they define effective photoluminescence and radioluminescence of the investigated Pb$_{\mathrm{1-X}}$Cd$_{\mathrm{X}}$I$_{2}$ alloys. Thus, the Pb$_{\mathrm{1-X}}$Cd$_{\mathrm{X}}$I$_{2}$ alloys can be considered as new scintillator materials, where the radioluminescence is determined by the emission of STEs in the layered semiconductor NCLs, and can be named bulk-nanostructured scintillators (or nanoscintillators). It should be noted that these nanoscintilators are strongly radiation-resistant. Our results may pave the way towards a new class of effective scintillator materials based on the emission of the STEs in the semiconductor NCLs. The further increase of the emission intensity of such nanoscintillator materials is possible by optimizing the size distribution of NCLs in the Pb$_{\mathrm{1-X}}$Cd$_{\mathrm{X}}$I$_{2}$ alloys and by means of thermoelectric cooling. [Preview Abstract] |
|
V1.00311: Commensurate solid phases of Krypton in carbon nanotubes Mamadou Mbaye, Silvina Gatica Recent experiments (Wang et al., 2010) have found evidence of phase transitions of gases adsorbed on a single carbon nanotube. Previous grand canonical Monte Carlo simulations of this system, for the cases of Ar and Kr on zigzag and armchair nanotubes with radius R $=$ 0.7 nm have resembled the experimental results in the case of Ar. However, the prominent, ordered phase found for Kr in both simulations and (classical) energy minimization calculations di\textunderscore ers from that deduced from the experimental data. A tentative explanation of the apparent discrepancy is that the experiments involve a nanotube of rather large radius (\textgreater 1.5 nm). We have extended our simulations to nanotubes of larger radius (1-3 nm), zigzag or armchair. In our simulations we found the formation of a layer of the same density than in the experiment, but we believe the layer is not a commensurate solid. [Preview Abstract] |
|
V1.00312: Enhanced thermoelectric figure of merit ($ZT$) of Te-doped FeSb$_2$ nanocomposite Mani Pokharel, Huaizhou Zhao, Machhindra Koirala, Zhifeng Ren, Cyril Opeil FeSb2 is considered as a potential candidate for Peltier cooling applications because of its colossal value of Seebeck coefficient (45,000 $\mu$VK$^{-1}$) at around 10 K. Our earlier works [1,2] showed that the \textit{ZT} values of undoped FeSb$_2$ nanocomposites could not be improved significantly despite of the drastic reduction in thermal conductivity which we attributed to the suppression of phonon-drag effect due to increased scattering of phonons off the grain-boundaries in nanocomposites. In this work, we demonstrate that combining nanostructuring approach with Te-doping further improves the thermoelectric properties to yield an enhanced \textit{ZT} value in FeSb$_2$ nanocomposites.\\[4pt] [1] Huaizhou Zhao, Mani Pokharel, Gaohua Zhu, Shuo Chen, Kevin Lukas, Qing Jie, Cyril Opeil, Gang Chen, and Zhifeng Ren; \textit{Appl. Phys. Lett.} 99, 163101 \textbf{(2011)}\\[0pt] [2] Mani Pokharel, Huaizhou Zhao, Kevin Lukas, Zhifeng Ren, and Cyril Opeil; \textit{Mater. Res. Soc. Symp. Proc. Vol. 1, 2012 DOI:10.1557/opl.2012.150 456 5} [Preview Abstract] |
|
V1.00313: Simulations of Concentrated Antibody Solutions and Comparison with Small-Angle Scattering Experiments Max Watson, Nicholas Clark, Joseph Curtis We have performed atomically detailed Monte-Carlo simulations of hundreds of antibodies in concentrated solutions. In order to compare our simulations with experiments, we developed a novel method for explicitly calculating the scattering intensity of these large systems. At various salt conditions and pH levels, the simulations are found to be in good agreement with small-angle X-ray scattering measurements for antibody concentrations exceeding 100 mg/mL. [Preview Abstract] |
|
V1.00314: Influence of spin correlations in the transport properties of a double quantum dot system Ignacio Hamad, Laercio Costa Ribeiro, Guillermo Chiappe, Enrique Victoriano Anda In this work we study the influence of spin correlations in the transport properties of a system consisting of two quantum dots (QDs) with high Coulomb interaction U which are interconnected through a chain of N non-interacting sites and individually coupled to two metallic leads. Using both the finite U slave boson mean field approach (FUSBMFA) and the Logarithmic-discretization-embedded-cluster approximation (LDECA) we studied the system in different regions of the parameter space for which we calculate many physical quantities, namely local density of states, conductance, total spin, spin correlations, in addition to the renormalization parameters associated with the FUSBMFA. The results reveled a very rich physical scenario which is manifested by at least two different Kondo regimes, the well-known spin s = 1/2 and some other type of Kondo effect which appears as a result of the coupling between the QDs and the non-interacting central sites. We also consider the possibility of accessing some kind of Kondo box effect due to the discrete nature of the central chain and study how this regime is affected by the magnetic interaction between the local spins of the QD's and by the interaction between these spins and the spins of the conduction electros in the leads. [Preview Abstract] |
|
V1.00315: Effect of Magnon-induced dephasing on spin transfer torque in magnetic tunnel junctions Farzad Mahfouzi, Branislav K. Nikolic In this work we investigate the effect of Electron-Magnon interaction on the spin transfer torque in magnetic tunnel junctions. We use Keldysh Green's function method and consider self consistent Born approximation (SCBA) with finite biased voltage to perform the calculation. We show that in some cases, excitation of the Magnons in the ferromagnet (FM) can enhance the spin transfer torque which is in addition to the increase of the switching rate due to existence of magnons in LLG equation. [Preview Abstract] |
|
V1.00316: Electronic properties of core-multishell semiconductor quantum wires Jusciane Silva, Andrey Chaves, Gil Farias, Robson Ferreira The effect of eccentricity distortions in the otherwise circular geometry of core-multishell quantum wires on their excitonic transitions is theoretically investigated. Within the effective mass approximation, the Schr\"odinger equation is numerically solved for electrons and holes in systems with single and double radial heterostructures, whereas the resulting exciton binding energy is calculated by means of a variational approach. Our results demonstrate that for a single shell heterostructure, in-plane electric fields applied in different directions produce qualitatively different energy spectra, which can be used to identify the eccentricity of the system. For a double heterostructure, the eccentricities of the inner and outer shells play an important role on the excitonic binding energy and on the oscillator strength. Our results also show that for a single shell heterostructure with a type-II confinement, i.e. with spatially separated electrons and holes, one of the carriers exhibits either a ring-like or a dot-like energy spectrum, depending on the radius of the system. In this case, a shell-to-core confinement transition for the electron can be induced also by an external magnetic field. [Preview Abstract] |
|
V1.00317: Stochastic models for cell division Evgeny Stukalin, Sean Sun The probability of cell division per unit time strongly depends of age of cells, i.e., time elapsed since their birth. The theory of cell populations in the age-time representation is systematically applied for modeling cell division for different spreads in generation times. We use stochastic simulations to address the same issue at the level of individual cells. Our approach unlike deterministic theory enables to analyze the size fluctuations of cell colonies at different growth conditions (in the absence and in the presence of cell death, for initially synchronized and asynchronous cell populations, for conditions of restricted growth). We find the simple quantitative relation between the asymptotic values of relative size fluctuations around mean values for initially synchronized cell populations under growth and the coefficients of variation of generation times. Effect of initial age distribution for asynchronous growth of cell cultures is also studied by simulations. The influence of constant cell death on fluctuations of sizes of cell populations is found to be essential even for small cell death rates, i.e., for realistic growth conditions. The stochastic model is generalized for biologically relevant case that involves both cell reproduction and cell differentiation. [Preview Abstract] |
|
V1.00318: Effects of Concentration of Precursor and Annealing Temperature on the Optical Properties of Nanostructured Al- doped Zinc Oxide (AZO) Thin films Prepared by Sol-Gel Spin Coating Technique Gbadebo T. Yusuf, Ayodeji O. Awodugba, Adepoju M. Raimi, Hezekiah O. Efunwole, Timothy O. Familusi This work investigates the effects of concentration of precursor and annealing temperature on the optical properties of nanostructured Al-doped (AZO) zinc oxide thin films prepared by sol-gel spin coating technique. The sols were prepared using concentration of zinc acetate dehydrate which was varied between 0.1 and 1.4 mole/liter. Aluminium chloride was used as dopant while the annealing temperature of 400$^{\circ}$ to 650$^{\circ}$ was chosen. The results show that the concentration between 0.3 to 0.6 moles/liter zinc acetate dehydrate in solution resulted in good thin films with high preferential c-axis orientation and optical transmission reveal a good transmittance within the visible wavelength spectrum region while the concentrations that fall outside this range did not yield films with good c-axis orientation. The films deposited at annealing temperatures 500$^{\circ}$ and 650$^{\circ}$ showed surface structures much smaller than 400$^{\circ}$. The Spin coating technique creates ZnO films with potential for application as transparent electrodes in optoelectronic devices such as solar cell. [Preview Abstract] |
|
V1.00319: Topological surface states on high-index Bi$_{2}$Se$_{3}$ epifilms grown by molecular-beam epitaxy on InP(001) Xin Guo, Zhongjie Xu, Mengyu Yao, Hongtao He, Lin Miao, Lu Jiao, Hongchao Liu, Jiannong Wang, Dong Qian, Jinfeng Jia, Wingkin Ho, Maohai Xie We use MBE to successfully grow a high-index Bi$_{2}$Se$_{3}$ (221) epifilm on InP(001) substrate. To facilitate growth of Bi$_{2}$Se$_{3}$ (221) on InP(001), the substrate has to undergo a careful thermal treatment. XRD and LEED measurements affirm the film to be of Bi$_{2}$Se$_{3}$ (221).The ARPES experiments on such a Bi$_{2}$Se$_{3}$(221) sample reveal unambiguously the linear dispersed surface states. In addition, the Fermi surface is elliptical rather than the more symmetrical one on Bi$_{2}$Se$_{3}$(111). Electrical transport studies of such (221) Bi$_{2}$Se$_{3}$ samples also show an anisotropy in two perpendicular directions in the plane of the surface. The longitudinal resistivity along the ``transverse'' direction is 1.9 $\sim$ 4.4 times higher than that along the ``parallel'' direction, and their ratios also depend on temperature from 2K to 300K. Hall resistances show non-linear field dependence at high temperature, implying multiband conduction. [Preview Abstract] |
|
V1.00320: Single Domain Bi$_{2}$Se$_{3}$ Films Grown on InP(111)A by Molecular-Beam Epitaxy X. Guo, Z.J. Xu, H.C. Liu, B. Zhao, X.Q. Dai, H.T. He, J.N. Wang, H.J. Liu, W.K. Ho, M.H. Xie We report the growth of single domain Bi$_{2}$Se$_{3}$(111) thin films by MBE on InP(111) substrate. On singular and vicinal substrate surfaces, we observe the 2D growth mode, as implied by the streaky RHEED patterns and the RHEED intensity oscillations. In the 2D step-flow growth mode, the epitaxial Bi$_{2}$Se$_{3}$ film is found to be diminished of twin and rotation domains, as inferable from both the unidirectional mounds seen by STM and by the three-fold LEED patterns. Such films show relatively low background doping ($\sim$ 1 $\times$ 10$^{18}$ cm$^{-3})$ and high low-temperature electron mobility (3500 cm$^{2}$V$^{\mathrm{-1}}$s$^{-1})$. Magnetoresistance measurements unveil SdH oscillations at different sample tilting angles. Ab initio total energy calculations suggest the existence of strong chemical interaction between atoms at the hetero-interface. Therefore, the growth does not proceed by the vdW epitaxy process. The additional chemical interaction between P and Bi atoms at steps would facilitate step-flow mode of growth, making the steps to offer an effective guide to the lattice of epitaxial Bi$_{2}$Se$_{3}$. [Preview Abstract] |
|
V1.00321: Ab-initio study of structural and electronic properties of thin film and bulk forms of Bi$_{2}$Q$_{3}$ (Q$=$ Se, Te) as topological insulators Ahmad Ranjbardizaj, Hiroshi Mizuseki, Yoshiyuki Kawazoe Bi$_{2}$Q$_{3}$ (Q$=$Se, Te) are the best-known bulk thermoelectric materials, which have been demonstrated to be topological insulators (TI). TI's are insulators with conductive surface states consisting of a single Dirac cones. These materials have layered structures consisting of stacked quintuple layers (QL), with relatively weak coupling between the QL's. Therefore, it might be easy to prepare the Bi$_{2}$Q$_{3}$ in the form of thin films with particular thicknesses using the available experimental techniques. In this study, the electronic and structural properties of bulk Bi$_{2}$Se$_{3}$ are investigated using density functional theory. Our results show that the Bi$_{2}$Se$_{3}$ is an indirect semiconductor with energy gap of $\approx $ 0.27 eV. Additionally, the electronic structure dependence of Bi$_{2}$Se$_{3\, }$to the thicknesses of thin films (n-QL's with n$=$1,2\textellipsis 9) is considered. It is observed that the electronic structure of this kind of thin films depends on the number of QL's. For n-QL's with n larger than three, the thin film has a bulk band gap and has protected conducting states on its surface. Moreover, the effect of number of layers (n) on band-gap energy is studied. Similar calculations and discussions are carried out for Bi$_{2}$Te$_{3}$ and the results are compared to the Bi$_{2}$Se$_{3}$ case and also the available theoretical and experimental results. [Preview Abstract] |
|
V1.00322: Creation of massive entanglement with optimized multiple spin squeezing Chao Shen, Luming Duan Quantum entanglement is an important resource in many areas such as precision measurement, quantum information processing and quantum computation. Controlled creation of quantum entanglement between a large number of particles is a goal to which significant theoretical and experimental efforts have been devoted. For a large collection of spins, spin squeezing is an experimentally relevant approach to entanglement creation. Two-axis spin squeezing was shown to achieve the Heisenberg limit for phase sensitivity, which scales as 1/N and N is the particle number. However the required Hamiltonian H=(Sy$^2$-Sx$^2$) is usually not readily available in experimental systems. Here we propose an optimized control scheme to approach the Heisenberg limit with only a single-axis spin squeezing Hamiltonian combined with an external magnetic field. Essentially the scheme consists of multiple spin squeezing with optimized parameters. And squeezing parameter achieved seems even better than two-axis squeezing. Moreover this scheme can be employed to prepare the |S, Sz$=0>$ Dicke state. [Preview Abstract] |
|
V1.00323: Effect of Stabilization and End Group Induced Charge Transfer on Frontier Molecular Orbital Reorganization - Applications to Molecular Thermoelectrics Janakiraman Balachandran, Pramod Reddy, Barry Dunietz, Vikram Gavini Endgroups play an important role in determining the thermopower and nature of transport across molecular junctions. In this work, we analyze the electronic structure of phenyl molecules coupled to gold electrodes through five different end groups. Accordingly we find that the direction of charge transfer is strongly correlated to the degree of reorganization of frontier molecular orbitals (FMOs) and in turn on the thermopower of molecular junctions. In particular, isocyanide, nitrile, and amine end-group molecular junctions, with charge (electron) transfer out of the molecule, exhibit a strong overall downward shift in the energies of frontier molecular orbitals, whereas thiol and hydroxyl end-group molecular junctions, with charge transfer into the molecule, exhibit a smaller overall downward shift. Two dominant factors namely (i)the stabilization effect due to contact with Au cluster and (ii) the change in electron-electron interactions due to charge transfer, determine the FMOs reorganization. We also provide a good estimate of the shift individually caused by each of these factors by performing a perturbation analysis. [Preview Abstract] |
|
V1.00324: Polarization Rotation by Multilayered Chiral Metamaterial Yumin Zhang Traditionally, negative permittivity was realized by plasma resonance of the metallic structures, and negative permeability was achieved by a resonant LC circuit. Chiral metamaterial is another route to achieve negative permittivity and permeability, and such structures were investigated at different frequency domains. Recently, it was demonstrated that a two-dimensional lattice of three-dimensional gold spirals can effectively block circular polarized light with the same handedness for a frequency range exceeding one octave. From the point of view of applications, metamaterials must be fabricated easily and cheaply, and one way to achieve this goal is planarization. We designed a multiple-layer quasi-helix PCB structure and had it fabricated. The sample was tested with automated free space microwave material measurement system at X-band. These layers of PCB can be arranged in two different configurations: left-handed or right- handed helix. We found that the polarization plane is rotated in the opposite direction for the left- and right-handed samples, and the measured S-parameters agree with the simulation result relatively well. [Preview Abstract] |
|
V1.00325: Fault tolerant quantum random number generator certified by Majorana fermions Dong-Ling Deng, Lu-Ming Duan Braiding of Majorana fermions gives accurate topological quantum operations that are intrinsically robust to noise and imperfection, providing a natural method to realize fault-tolerant quantum information processing. Unfortunately, it is known that braiding of Majorana fermions is not sufficient for implementation of universal quantum computation. Here we show that topological manipulation of Majorana fermions provides the full set of operations required to generate random numbers by way of quantum mechanics and to certify its genuine randomness through violation of a multipartite Bell inequality. The result opens a new perspective to apply Majorana fermions for robust generation of certified random numbers, which has important applications in cryptography and other related areas. [Preview Abstract] |
|
V1.00326: Magnetic Behavior of Ni-Fe Core-Shell and Alloy Nanowires Jagnyaseni Tripathy, Jose Vargas, Leonard Spinu, John Wiley Template assisted synthesis was used to fabricate a series of Ni-Fe core-shell and alloy nanowires. By controlling reaction conditions as well as pore structure, both systems could be targeted and magnetic properties followed as a function of architectures. In the core-shell structure coercivity increases with decrease in shell thickness while for the alloys, coercivity squareness improve with increase pore diameter. Details on the systematic studies of these materials will be presented in terms of hysteretic measurements, including first order reversal curves (FORC), and FMR data. Magnetic variation as a function of structure and nanowire aspect ratios will be presented and the origins of these behaviors discussed. [Preview Abstract] |
|
V1.00327: Nondegradative Dielectric Coating of Graphene using Thermal Evaporation of SiO Seiya Suzuki, Chien-Chung Lee, Takashi Nagamori, Thomas Schibli, Masamichi Yoshimura Deposition of dielectrics onto graphene is a challenging technique due to the difficulties of fabricating high quality oxide on pristine graphene without introducing atomic defects. Here we report on a novel method to fabricate silicon oxide layer on graphene by vacuum thermal evaporation of silicon monoxide (SiO). Raman spectroscopy and mapping showed the present method did not degrade graphene, in contrast to the e-beam evaporated SiO$_{\mathrm{2}}$ coating method previously reported. We fabricated graphene field effect transistor devices with four metal electrodes to measure gate voltage dependence of sheet resistance of the graphene, and deposited a top coating of SiO on the graphene channel. The electrical measurements before and after the top-coating revealed that the top coating suppressed chemical shift of the graphene from strong p-dope to nearly undoped. Since SiO is transparent for visible and infrared light, the coating can be available as a protection layer for optical devices of graphene such as photodetectors and electro-optic modulators. Since the SiO top coating is a simple vacuum evaporation, it is much easier than atomic-layer-deposition which requires additional functionalization of graphene, and compatible with industrial use. [Preview Abstract] |
|
V1.00328: Optical investigation of redox properties of amorphous V$_{2}$O$_{5}$ thin films Jong-Gul Yoon, Tae Dong Kang, Tae Won Noh We report a high sensitivity of the optical properties of amorphous V$_{2}$O$_{5}$ thin films to redox reaction. Temperature dependence of spectroscopic ellipsometry data showed that the amorphous V$_{2}$O$_{5}$ films were optically anisotropic and the optical constants of the films changed irreversibly in high vacuum at around 420-480 K. Formation of oxygen vacancies in V$_{2}$O$_{5}$ film by the reduction process may result in the anisotropic changes in the optical constants and optical band gaps. Layered structure of V$_{2}$O$_{5}$ and structural relaxation by the formation of vanadyl oxygen vacancies were attributed to the optical anisotropy and the changes in the optical properties, respectively. [Preview Abstract] |
|
V1.00329: Highly Transparent Water-Repelling Surfaces based on Biomimetic Hierarchical Structure Sanghyuk Wooh, Jai Hyun Koh, Hyunsik Yoon, Kookheon Char Nature is a great source of inspiration for creating unique structures with special functions. The representative examples of water-repelling surfaces in nature, such as lotus leaves, rose petals, and insect wings, consist of an array of bumps (or long hairs) and nanoscale surface features with different dimension scales. Herein, we introduced a method of realizing multi-dimensional hierarchical structures and water-repellancy of the surfaces with different drop impact scenarios. The multi-dimensional hierarchical structures were fabricated by soft imprinting method with TiO$_{2}$ nanoparticle pastes. In order to achieve the enhanced hydrophobicity, fluorinated moieties were attached to the etched surfaces to lower the surface energy. As a result, super-hydrophobic surfaces with high transparency were realized (over 176$^{\circ}$ water contact angle), and for further investigation, these hierarchical surfaces with different drop impact scenarios were characterized by varying the impact speed, drop size, and the geometry of the surfaces. [Preview Abstract] |
|
V1.00330: SIR Fronts in Complex Networks with Metapopulation Structure Jason Hindes, Sarabjeet Singh, Chris Myers, Dave Schneider SIR dynamics has been studied extensively on complex networks, yielding insight into the effects of heterogeneity in contact patterns on the spread of infectious diseases. Separately, metapopulations have provided a paradigm for modeling systems with extended and ``patchy'' organization. In this paper we demonstrate how multi-type networks can be used to combine these paradigms such that simple disease dynamics models can include heterogeneity in connectivity and multi-scale structure. We first present a multi-type generalization of the Volz-Miller mean-field approximation for SIR dynamics on multi-type random graphs. We then use this technique to study the propagation of epidemic fronts in a simple metapopulation model with population centers composed of configuration model networks coupled on a one-dimensional lattice. Using the formalism of front propagation into unstable states, we derive the effective transport coefficients of the linear spreading: asymptotic speed, characteristic perturbation size, and diffusion coefficient for the pulled fronts, and explore their dependence on the underlying graph structure. We also derive the average steady-state incidence, the equilibrium spectrum, and the threshold for invasion. [Preview Abstract] |
|
V1.00331: Electron-tunneling measurements of low-Tc single-layer Bi-2201 cuprates Th. Jacobs, S.O. Katterwe, H. Motzkau, A. Rydh, A. Maljuk, T. Helm, M.V. Kartsovnik, C. Putzke, E. Kampert, V.M. Krasnov The single-CuO$_2$ plane cuprate superconductor Bi$_{2+x}$Sr$_{2-y}$CuO$_{6+\delta}$ (Bi-2201) is characterized by a low critical temperature and a relatively low upper critical field. This allows a complete suppression of superconductivity even at low $T$ and opens a possibility to study the normal-state properties with a relatively low interference of thermal fluctuations. Furthermore, the understanding of $T_c$ suppression in Bi-2201 is of great significance for understanding the mechanism of high $T_c$ in other cuprates. We present intrinsic tunneling and high magnetic field (up to 65 T) transport measurements of Bi-2201 single crystals with a $T_c$ of only $\sim 4$ K. All superconducting characteristics are reduced proportional to $T_c$, but the corresponding $c$-axis pseudogap characteristics remain similar to that in high-$T_c$ Bi-2212 and Bi-2223 compounds with 20-30 times larger $T_c$. This scaling disparity reveals the different origin of superconducting and pseudogap states. We also conclude that the low $T_c$ in our Bi-2201 crystals is not caused by strong thermal fluctuations at low $T$, nor by crystal defects, but is the consequence of a weaker coupling, leading to a small Cooper pair energy. [Preview Abstract] |
|
V1.00332: Universal functions for the transport properties through nanostructured devices Lucas Sala, Luiz N. Oliveira A renormalization-group analysis of the temperature-dependent transport properties of a nanostructured device will be presented. To be specific, the single-electron transistor geometry, in which a quantum dot bridges two otherwise independent electron gases, will be considered. The renormalization-group analysis will consider the equilibrium electrical and thermal conductances and the thermopower in the Kondo regime and will be based on the spin-degenerate Anderson model for the device. The three properties can be related to the three lowest energy moments $\mathcal{L}_j$ ($j=0,1,2$) of the temperature-dependent spectral density of the dot level. We will rigorously show that each moment $\mathcal{L}_j$ maps linearly onto a universal function $L_{j}$ of the temperature scaled by the Kondo temperature $T_K$, with linear coefficients determined by the ground-state occupation of the quantum dot. Essentially exact numerical renormalization-group results for each of the three universal functions will be presented, showing that they can be related to each other at relatively high temperatures, $T>T_K$. The results will be compared to previous theoretical studies of the transport properties, and the implications concerning the interpretation of experimental data will be discussed. [Preview Abstract] |
|
V1.00333: Oscillatory Rheology near Jamming Simon Dagois-Bohy, Brian Tighe, Ellak Van Somfai, Martin Van Hecke Granular matter is known to exhibit rich mechanical features close to the jamming transition. These features have been explored extensively with quasi-static approaches in the past 10 years. We explore now the dynamical axis, and look at the form of the complex shear modulus in numerical packings of soft spheres, when submitted to a strain oscillating in time. As predicted by B. Tighe (PRL 107, 158303 (2011)) we find that close to the jamming transition, an anomalous scaling regime appears, where both storage and loss moduli grow as the square root of the frequency, and this even when inertia is taken into account. Finally, higher forcing allows to explore non-linearities in these systems, as well as complex reversibility and memory effects. [Preview Abstract] |
|
V1.00334: Dissipative Particle Dynamics Method on PH-Responsive Polymeric Drug Delivery System Yingying Guo The self-assembled morphologies formed by polymer in selective solvent could be potentially used as drug-delivery vehicles and has attracted great attention recently. In our work, the drug release mechanism of polymeric delivery vehicle (polymeric microsphere) is investigated with Dissipative particle dynamics simulation. Poly (Lactic Acid)-b-polyethylene glycol (PLA-b-PEG) diblock copolymer is the carrier while IBU is selected as the model drug. A core-shell spherical micelle with drug encapsulated in the core is obtained in our simulation. By changing the medium from neutral to acid, the drugs release via a diffuse mechanism. Both the formation mechanism of the encapsulant and the release mechanism for the drugs are studied in our work. For the formation process, it can be ascribed as the coalesce of the small clusters and the disperse of the drugs; while for the drug release behavior, the process can be divided for three stages: (1) swell of the polymeric carrier, (2) drug diffuse in the carrier and some acid molecules disperse into the carrier, (3) drug release towards the acid medium. Our results might provide a mesoscopic methodology for the evaluation and prediction for polymeric self-assemblies as a carrier for pharmaceutical interest. [Preview Abstract] |
|
V1.00335: Non-thermal excitation and control of dynamic magnetization in a Fe/GaAs heterojunction by ultrafast laser pulses Yu Gong, A.R. Kutayiah, Z. Cevher, X.H. Zhang, J.H. Zhao, Y.H. Ren Control carrier injection in metal semiconductor heterojunctions and therefore their magnetic dynamics is a major challenge in modern solid-state electronic devices. We report on our recent study of non-thermally excitation and coherently control the spin reorientation by utilizing low-energy femtosecond laser pulses to induce a photo- current through a Fe/GaAs interface. The magnetization dynamics and hysteresis curves were recorded by the pump-probe differential magnetic Kerr (DMK) technique. We show that magnetization excitation and reorientation strongly depend on the polarization of pump pulses. A clear four-fold switching is identified in DMK signal when we rotate the polarization of pump pulses. Our results show that the dynamic magnetization can be induced and controlled by ultrafast laser pulses, and therefore indicate the feasibility of next generation femtosecond-switching magnetic storage devices. [Preview Abstract] |
|
V1.00336: Time reversal of optical pulses by adiabatic coupling modulation in Coupled-Resonator Optical Waveguides Chao Wang, Christopher Search We propose a method to time reverse optical pulses in Coupled-Resonator Optical Waveguides(CROW) by adiabatically modulating the couplings between constituent microcavities. Time reversal, also known as phase conjugation, is an inversion of the optical phase. Currently, nonlinear four-wave mixing is the primary method to realize time reversal, but the need for phase matching makes it unsuitable for broadband optical pulses and in integrated devices. Therefore time reversal of both narrow pulses and in photonic circuits are still unsolved problems. Our method to overcome these difficulties is to tune the sign of the inter-resonator evanescent couplings $\kappa$ of a CROW, whose dispersion is proportional to $\kappa$. A Mach-Zehnder Interferometer inserted into the coupling region can tune $\kappa$ by either electro-optic or thermo-optic modulation of the interferometer phase. For small modulations of the phase around $\pi$, time reversal is realized as a result of sign reversal of $\kappa$. The bandwidth of the pulses that can be time reversed is limited only by the resonators' Q-factor and free spectral range. Simulations based on coupled mode equations of Si microring resonators show that picosecond pulses can be time reversed with good fidelity for Q-factors as low as $10^{5}$. [Preview Abstract] |
|
V1.00337: Nonlinear Kerr enhancement of the Sagnac effect in a coherently coupled array of optical microresonators Chao Wang, Christopher Search Optical gyroscopes based on the Sagnac effect are of great interest both theoretically and practically. Previously it has been suggested a nonlinear Kerr medium inserted into a ring resonator gyroscope can largely increase the rotation sensitivity due to an instability caused by the non-reciprocal self-phase and cross-phase modulations. Recently, coupled microresonator arrays such as Side-Coupled Integrated Spaced Sequence of Resonators (SCISSOR) and Coupled Resonator Optical Waveguides (CROW) have drawn interest as potential integrated gyroscopes due to the sensitivity enhancement resulting from distributed interference between resonators. Here we analyze a SCISSOR system, which consists of an array of microresonators evanescently coupled to two parallel bus waveguides in the presence of a strong intra-resonator Kerr nonlinearity. We show that the distributed interference in the waveguides combined with the nonlinearly enhanced Sagnac effect in the resonators can further improve the sensitivity compared with either a single resonator of equal footprint or SCISSOR without a Kerr nonlinearity. Numerical simulation shows that bistability in the SCISSOR occurs and the rotation sensitivity $\frac{dI_{output}}{d\omega }$ can go to infinity near the boundaries of the bistable region. [Preview Abstract] |
|
V1.00338: Refraction and reflection process in a ferromagnet/frustrated-ferromagnet junction Hiroaki Ueda, Yuta Sasaki The refraction and reflection process plays an important role in controlling a propagation of spinwave. In this presentation, we study the refraction and reflection process of spinwave in the junction of the (usual) ferromagnet/frustrated ferromagnet junction. Frustration induces a nontrivial dispersion relation of spinwave even in the fully polarized ferromagnet phase. As a result, we find exotic refraction processes such as the splitting of spin waves and the negative refraction. [Preview Abstract] |
|
V1.00339: Active electromagnetic metamaterial based on spin torque oscillators Hiroaki Ueda, Gen Tatara, Katsuhisa Taguchi, Yuta Sasaki, Miyuki Nishijima, Akihito Takeuchi We propose theoretically an active material for electromagnetic radiation with frequency of GHz by use of spin-torque oscillators. The origin of the amplification is the energy supplied to the magnetization by the injected current. We show that close to a resonance with current-driven magnetization, the imaginary part of magnetic permeability becomes indeed negative for either of the two circular polarizations, resulting in negative imaginary part of refractive index. Besides, the real part of the refractive index is also manipulated by the current. Our system thus realizes an active filter to obtain circular polarized radiation and/or an electromagnetic metamaterial having negative refractive index, both controlled electrically. [Preview Abstract] |
|
V1.00340: Nematic phase and phase separation near saturation field in frustrated ferromagnets Hiroaki Ueda, Tsutomu Momoi We discuss effects of quantum fluctuations on magnetization process of quantum frustrated ferromagnets. It is found that, on general grounds, in a neighborhood of a ferromagnet/antiferromagnet classical 1st-order phase boundary in zero external field, a phase separation or non-classical phase must appear slightly below the saturation field in a quantum case, if the classical AF is not an eigenstate. Besides, we study the ferromagnetic $J_1$-$J_2$ $S=1/2$ Heisenberg model ($J_1<0$) on the bcc lattice from the viewpoint of the magnon Bose-Einstein condensation. For $-1.50097 \leq J_1/J_2 \leq -1.389$, the nematic phase is expected and for $-1.389 \leq J_1/J_2 \leq -0.48$ the phase separation appears under high magnetic field. [Preview Abstract] |
|
V1.00341: Magnetic Tethering of Microswimmers in Microfluidic Devices Aschvin Chawan, Saikat Jana, Suvojit Ghosh, Sunghwan Jung, Ishwar K. Puri Exercising control over animal locomotion is well known in the macro world. In the micro-scale world, such methods require more sophistication. We magnetize Paramecium multimicronucleatum by internalization of magnetite nanoparticles coated with bovine serum albumin (BSA). This enables control of their motion in a microfluidic device using a magnetic field. Miniature permanent magnets embedded within the device are used to tether the magnetized organisms to specific locations along a micro-channel. Ciliary beatings of the microswimmer generate shear flows nearby. We apply this setup to enhance cross-stream mixing in a microfluidic device by supplementing molecular diffusion. The device is similar to an active micromixer but requires no external power sources or artificial actuators. We optically characterize the effectiveness of the mechanism in a variety of flow situations. [Preview Abstract] |
|
V1.00342: Effect of Ion Binding in Palmitoyl-Oleoyl Phosphatidylserine Monolayers Matthew Eckler, Silvina Matysiak Molecular dynamics simulations of palmitoyl-oleoyl phosphatidylserine (POPS) monolayers at the air-water interface were performed with different ionic strengths with the aim of determining the specific organization and dynamics of counterion binding events. Na$+$ ions penetrated the monolayers into both the ester carbonyl and carboxylate regions of the phospholipids. The~binding events increase with the addition of salt. Differences in lipid order parameter, headgroup orientation, and~prevalence of inter- and intramolecular hydrogen bonding events between the amine group of the lipid and oxygen groups are observed depending on whether the Na$+$ is binding near the carboxylate or ester region of the lipid. The observed changes are explained in terms of the salting-out effect. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700