Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session G1: Poster Session I (Tuesday, 2:00 pm - 5:00 pm)Poster Undergraduate
|
Hide Abstracts |
Room: Exhibit Hall EF |
|
G1.00001: APPLICATIONS |
|
G1.00002: Simple thermal treatment for the size control of pore arrays in a polystyrene colloidal crystal films Ryan M. Jamiolkowski, Shane A. Fiorenza, Kevin Chen, Alyssa M. Tate, Shawn H. Pfeil, Yale E. Goldman Nanosphere Lithography (NSL) offers an attractive route to fabricating periodic structures with nanoscale features, without e-beam or deep UV lithography. In particular, it is uniquely suited to the low cost fabrication of large repeated arrays pores or pillars created by taking advantage of the interstitial spaces in close-packed monolayers of nano to micro-scale beads. However pore size, shape, and spacing cannot be controlled independently. We present both a robust method for producing large, approximately 1 cm$^{2}$, hexagonally close packed monolayer films of 1 micron diameter polystyrene beads on glass substrates, and thermal treatment of these films near the glass temperature, T$_{g}$, of polystyrene to modify the pore size. This builds on earlier work showing that pore size can be modified for colloidal crystals formed at a liquid gas interface [2]. These processes promise a simple, reproducible, and low cost route to periodic pore arrays for nano-photonic applications such as zero mode waveguides (ZMWs) [Preview Abstract] |
|
G1.00003: Synthesis of Novel Birnessite Type MnO$_{\mathrm{2}}$ Nanochains by Electrospinning and their Application as Supercapacitor Electrodes Muhamed Shareef, Milan Palei, Samerender Hanumantha Rao, Tirupattur Natarajan, Gurpreet Singh A first time method for the synthesis of continuous nanochains by employing electrospinning and post processes are reported with theoretic support. High aspect ratio electrospun PAN nanofibers were stabilized in air at a specific heating rate followed by functionalization in aqueous KMnO$_{\mathrm{4}}$ solution. The composite membrane was calcined in air in order to remove polymer skeleton along with reduction of KMnO$_{\mathrm{4}}$ into MnO$_{\mathrm{2}}$. The highly crystalline and phase pure birnessite type MnO$_{\mathrm{2}}$ nanochains were characterized by different microscopic and spectroscopic techniques. Electrochemical studies of these nanochains were carried out using three electrode and two electrode set up with 0.5 M Na$_{\mathrm{2}}$SO$_{\mathrm{4}}$ aqueous electrolyte. A possible mechanism for the formation of nanochains was also explained [Preview Abstract] |
|
G1.00004: Spin torque resonant vortex core expulsion for an efficient radio-frequency detection scheme V. Cros, A.S. Jenkins, R. Lebrun, P. Bortolotti, E. Grimaldi, S. Tsunegi, H. Kubota, K. Yakushiji, A. Fukushima, S. Yuasa It has been proposed by Tulaparkur et al.[1ref] that a high frequency detector based on the so called spin-diode effect in spin transfer oscillators could eventually replace conventional Schottky diodes, due to their nanoscale size, frequency tunability, and large output sensitivity. Although a promising candidate for ICT applications, the output voltage generated from this effect is consistently low. Here we present a scheme for a new type of spintronics-based high frequency detector based on the expulsion of the vortex core of a magnetic tunnel junction. The resonant expulsion of the core leads to a large and sharp change in resistance associated with the difference in magnetoresistance between the vortex ground state and the final C-state, which is predominantly in either the parallel or anti-parallel direction relative to the polariser layer [2]. Interestingly, this reversible effect is independent of the incoming rf current amplitude, offering a compelling perspective for a fast real-time rf threshold detector. REF : EU FP7 grant (MOSAIC No. ICT-FP7-317950 is acknowledged. [1] Tulapurkar et al. Nature 438, 339, [2] A.S. Jenkins et al., Nat. Nanotech (2015) [Preview Abstract] |
|
G1.00005: Physics Incubator at Kansas State University Bret Flanders, Amitabha Chakrabarti Funded by a major private endowment, the physics department at Kansas State University has recently started a physics incubator program that provides support to research projects with a high probability of commercial application. Some examples of these projects will be discussed in this talk. In a parallel effort, undergraduate physics majors and graduate students are being encouraged to work with our business school to earn an Entrepreneurship minor and a certification in Entrepreneurship. We will discuss how these efforts are promoting a ``culture change'' in the department. We will also discuss the advantages and the difficulties in running such a program in a Midwest college town. [Preview Abstract] |
|
G1.00006: Radiation Pattern and Scattering Properties of Optical Antennas Zeyan Xu, Kevin Messer, Eli Yablonovitch When light emitting devices (e.g. LEDs) are coupled with optical antennas of the same resonance frequency, their spontaneous emission rate can be enhanced drastically. The ultimate goal is to have the rate of spontaneous emission faster than the stimulated emission so that the LEDs would be as fast as lasers and enable us to achieve energy efficient interconnects for on-chip communication. In this project, we built multiple optical setups to experimentally measure the far field radiation pattern, light scattering properties and photoluminescence of a series of optical antennas. We also used Lumerical FDTD software to theoretically simulate the structure and found out that the simulated results agree with experimental values. As the longitudinal length increased, the spectrum shifted towards higher wavelengths on the spectrum. Also, by studying the radiation patterns of the optical antennas, we are able to understand their strengths as a function of direction, and how the geometrical shape contribute to the shape of radiation patterns. Understanding the radiation pattern and the scattering spectrum of optical antennas will enable us to design devices with specific requirements on radiational directions and resonance frequencies for optical antennas. [Preview Abstract] |
|
G1.00007: Visible WGM emissions from rare earth ion doped ZnO microspheres Fabitha K, M S Ramachandra Rao ZnO is known to be an ideal candidate for short wavelength range opto-electronic device applications due to its wide and direct bandgap (3.37 eV) and high excitonic binding energy (60 meV). Apart from the UV emission at \textasciitilde 380 nm (free exciton emission) ZnO also possesses a broad emission band centered at \textasciitilde 530 nm which is expected to be originated from the oxygen vacancy (Vo) defects. In rare earth (RE) ion doped ZnO, emissions originate from the 4f levels of RE ions will be obtained in addition to the characteristic emissions of ZnO. Small micro/nanostructures made of ZnO with high crystalline quality show unique characteristics in light emission, especially in lasing applications. A micro/ nanostructured ZnO crystal generally has a wurtzite structure with a natural hexagonal cross section, which serves as a WGM lasing micro cavity owing to its high reflective index ($\sim $2). However, there exists a potential optical loss at corners of hexagons; therefore, an isotropic structure like spheres may be a better candidate to achieve efficient light confinement. In our work, highly smooth micro spheres with different diameters were grown. Raman spectroscopy measurements confirm the hexagonal wurtzite structure of ZnO, SEM and AFM studies shows the smooth surfaced spheres. WGM lasing characteristics of ZnO spheres have been investigated using optical pumping with 488 nm laser in a micro-PL system. Details of the results will be presented. [Preview Abstract] |
(Author Not Attending)
|
G1.00008: Title: Development of Single photon Quantum Optical Experiments using Type-I and Type-II Spontaneous Parametric Down Conversion Andrew Laugharn, Seyfollah Maleki We constructed a quantum optical apparatus to control and detect single photons. We generated these photons via Type-I and Type-II spontaneous parametric down conversion by pumping a GaN laser (405nm) incident on a BBO crystal. We detected the two down converted photons (810nm), denoted signal and idler, in coincidence so as to measure and control single photons. We implemented a coincidence counting unite onto an Altera DE2 board and used LabView for data acquisition. We used these photon pairs to demonstrate quantum entanglement and indistinguishability using multiple optical experiments. [Preview Abstract] |
|
G1.00009: High speed Infrared imaging method for observation of the fast varying temperature phenomena Reza Moghadam, kambiz Alavi, Baohong Yuan With new improvements in high-end commercial R{\&}D camera technologies many challenges have been overcome for exploring the high-speed IR camera imaging. The core benefits of this technology is the ability to capture fast varying phenomena without image blur, acquire enough data to properly characterize dynamic energy, and increase the dynamic range without compromising the number of frames per second. This study presents a noninvasive method for determining the intensity field of a High Intensity Focused Ultrasound Device (HIFU) beam using Infrared imaging. High speed Infrared camera was placed above the tissue-mimicking material that was heated by HIFU with no other sensors present in the HIFU axial beam. A MATLAB simulation code used to perform a finite-element solution to the pressure wave propagation and heat equations within the phantom and temperature rise to the phantom was computed. Three different power levels of HIFU transducers were tested and the predicted temperature increase values were within about 25{\%} of IR measurements. The fundamental theory and methods developed in this research can be used to detect fast varying temperature phenomena in combination with the infrared filters. [Preview Abstract] |
|
G1.00010: Room temperature lasing in GeSn alloys: A path to CMOS-compatible infrared lasers$\backslash $ Zairui Li, Yun Zhao, James Gallagher, José Menéndez, John Kouvetakis, Imad Agha, Jay Mathews h $-abstract-$\backslash $pard The semiconductor industry has been pushing silicon photonics development for many years, resulting in the realization of many CMOS-compatible optoelectronic devices. However, one challenge that has not been overcome is the development of Si-based lasers. Recently, GeSn alloys grown on Si have shown much promise in the field of infrared optoelectronics. These alloy films are compatible with CMOS processing, have band gaps in the infrared, and the band structure of GeSn can be tuned \textit{via} Sn concentration to induce direct band gap emission.$\backslash $pard In this work, we report on room temperature lasing in optically-pumped waveguides fabricated from GeSn films grown epitaxially on Si(100) substrates. The waveguides were defined using standard UV photolithography and dry-etched in a Cl plasma. The end facets were mirror polished, and Al was deposited on one facet to enhance cavity quality. The waveguides were optically-pumped using a 976nm wavelength solid-state laser, and the corresponding emission was measured. The dependence of the emission power on the pump power shows a clear transition between spontaneous and stimulated emission, thereby demonstrating room temperature lasing.$\backslash $pard$\backslash $pard-/abstract-$\backslash $\tex [Preview Abstract] |
|
G1.00011: Field-induced activation of metal oxide semiconductor for low temperature flexible transparent electronic device applications Pushpa Raj Pudasaini, Joo Hyon Noh, Anthony Wong, Amada Haglund, Thomas Zac Ward, David Mandrus, Philip Rack Amorphous metal-oxide semiconductors have been extensively studied as an active channel material in thin film transistors due to their high carrier mobility, and excellent large-area uniformity. Here, we report the athermal activation of amorphous indium gallium zinc oxide semiconductor channels by an electric field-induced oxygen migration via gating through an ionic liquid. Using field-induced activation, a transparent flexible thin film transistor is demonstrated on a polyamide substrate with transistor characteristics having a current ON-OFF ratio exceeding 108, and saturation field effect mobility of 8.32 cm2/(V.s) without a post-deposition thermal treatment. This study demonstrates the potential of field-induced activation as an athermal alternative to traditional post-deposition thermal annealing for metal oxide electronic devices suitable for transparent and flexible polymer substrates. [Preview Abstract] |
|
G1.00012: Dependence of superconducting properties of NbN thin films on sputtering parameters. Trupti Khaire, Faustin Carter, Junjia Ding, Chrystian Posada, Amy Bender, Gensheng Wang, Volodymyr Yefremenko, John Pearson, Steve Padin, Clarence Chang, Axel Hoffmann, Valentyn Novosad Recently, there has been growing interest in utilizing NbN, TiN, NbTiN thin films in superconducting device applications (e.g. detectors for CMB, mm and sub-mm astronomy). In this work, we have fabricated NbN superconducting thin films by DC reactive magnetron sputtering of Nb in the presence of argon and nitrogen gases. We found that the critical temperature of NbN films is sensitive to various deposition parameters like nitrogen flow rate, target voltage, base pressure, RF substrate bias, and the substrate temperature. By studying each of these factors we have been able to create highly reproducible NbN thin films. We obtained a Tc of 15.25$+$/-0.25 K for 300 nm thick NbN film grown on silicon substrate at modest temperature of 250 C in the presence of RF substrate bias. We are also investigating the microwave properties of these NbN films at temperatures well below 50 mK by fabricating quarter wavelength CPW resonators out of NbN and characterizing their frequency shifts and quality factors as functions of temperature and power. In this work we present the results of these analyses. [Preview Abstract] |
|
G1.00013: Nano crystalline palladium disposable electrode development for electrochemical spectroscopy application Wei Chen, Chien-Hao Su, Peng-Jen Chen, Kuo-Chen Hsu, Chia-Ching Chang Electrochemical spectroscopy is a highly sensitive and selective detection method to revealing the intermolecular interaction. Gold electrode provides excellent charge transfer property and has been widely used in electrochemical analysis. However, gold electrode is expensive. Moreover, it is time consuming and complicated to regenerate a reaction active gold electrode. Therefore, a ready-to-use electrode is highly desired for electrochemical analysis. In this study, we have developed a novel nano-crystalline palladium (Pd) film electrode which is deposited on flexible polyethylene terephthalate (PET) by sputtering. This Pd electrode is as good as well prepared gold electrode both in cyclic voltammetry (CV) and electric impedance spectroscopy (EIS) due to its highly dispersive \textbraceleft 1 1 1\textbraceright facets-exposed nanocrystalline Pd on high quality. By using this ready-to-use Pd film electrode, the interactions between DNA and drugs can be detected at sub-nanogram level. [Preview Abstract] |
|
G1.00014: Nanopore gating with an anchored polymer in a switching electrolyte bias Craig Wells, Ining Jou, Dmitriy Melnikov, Maria Gracheva We theoretically study the interaction between a tethered, negatively charged polymer chain of varying lengths and a solid state membrane with a nanopore when subject to a time-dependent applied electrolyte bias. Brownian dynamics is used to describe the movement of a biomolecule interacting with a membrane immersed in an electrolyte solution. With the help of an applied electrolyte bias, we can control polymer's equilibrium position, extending it inside the pore for a sufficiently positive bias. We find that the amount of time a polymer takes to enter and extend inside a nanopore in a positive bias increases nearly linearly with the chain length, corresponding to an electrically driven process. The time it takes for the chain to exit the pore, however, increases nearly quadratically with chain length, corresponding to a diffusion process. Understanding the dynamical behavior of the tethered polymer chain will facilitate further advances in this area of nanotechnology. [Preview Abstract] |
|
G1.00015: Nanoindentation of Chitosan Doped with Silver Nanoparticles Matthew Palumbo, Alem Teklu, Narayanan Kuthirummal, Nicole Levi-Polyachenko Imaging and spectroscopic analysis via nanoindentation was performed with the Nanosurf EasyScan2 AFM on the pure and silver doped chitosan samples allowing for a more localized determination of their stiffness, hardness, and reduced Young's modulus. The pure chitosan sample was tested to have a stiffness of 0.367 N/m, a hardness of 1.12 GPa, and a reduced Young's modulus of 30.5 MPa. The film with 5mg Ag nanoparticle per gram of chitosan was tested on the boundaries between the chitosan and Ag nanoparticles to show an increase in stiffness of about 4.6{\%} at 0.384 N/m, an increase in hardness of about 5.4{\%} at 1.18 GPa, and an increase in the reduced Young's modulus of about 5.0{\%} at 3.2 MPa in comparison to the pure chitosan sample. On the other hand, upon increasing the doping to 10mg Ag nanoparticle per gram of chitosan showed a decrease in stiffness of about 6.3{\%} at 0.344 N/m, a decrease in hardness of about 27.0{\%} at 0.820 GPa, and a decrease in the reduced Young's modulus of about 6.0{\%} at 28.7 MPa in comparison to the pure chitosan sample. Obviously, films doped with 5mg Ag nanoparicle per gram of chitosan provided the composites with improved mechanical strength compared to chitosan alone. [Preview Abstract] |
|
G1.00016: Thin film metallic sensors in an alternating magnetic field for magnetic nanoparticle hyperthermia cancer therapy Z. A. Hussein, Z. Boekelheide In magnetic nanoparticle hyperthermia in an alternating magnetic field for cancer therapy, it is important to monitor the temperature in situ. This can be done optically or electrically, but electronic measurements can be problematic because conducting parts heat up in a changing magnetic field. Microfabricated thin film sensors may be advantageous because eddy current heating is a function of size, and are promising for further miniaturization of sensors and fabrication of arrays of sensors. Thin films could also be used for in situ magnetic field sensors or for strain sensors. For a proof of concept, we fabricated a metallic thin film resistive thermometer by photolithographically patterning a 500{\AA} Au/100{\AA} Cr thin film on a glass substrate. Measurements were taken in a solenoidal coil supplying 0.04 T (rms) at 235 kHz with the sensor parallel and perpendicular to the magnetic field. In the parallel orientation, the resistive thermometer mirrored the background heating from the coil, while in the perpendicular orientation self-heating was observed due to eddy current heating of the conducting elements by Faraday’s law. This suggests that metallic thin film sensors can be used in an alternating magnetic field, parallel to the field, with no significant self-heating. [Preview Abstract] |
|
G1.00017: Effect of pore's geometry on the electroosmotic flow and nanoparticle dynamics in the nanopore Zachery Hulings, Dmitriy Melnikov, Maria Gracheva We theoretically study how the electroosmotic fluid velocity in a charged cylindrical nanopore in a solid state membranes depends on the pore's geometry, electrolyte concentration, and applied electrolyte bias. We find that in long pores, the fluid velocity follows the classical von Smoluchowski result for an infinite pore with a maximum along the pore axis. However, when the pore's length is comparable to its diameter, the velocity profile develops a local minimum along the pore axis with a maximum value near the membrane walls. The minimum becomes more pronounced when the electrolyte concentration and/or applied bias become larger. We attribute this effect to the inhomogeneous electric field distribution in the nanopore with the field along the axis of the pore being smaller than along the pore's walls due to the effects of access resistance on each side of the channel. We also investigate repercussions of such a velocity profile on the transport of a nanoparticle through the nanopore. [Preview Abstract] |
|
G1.00018: Thermocouples in an alternating magnetic field (AMF) for studying magnetic nanoparticle hyperthermia S. Hartzell, Z. Boekelheide Magnetic nanoparticle hyperthermia, a method of cancer therapy, is currently a subject of active research. A critical parameter during therapy or laboratory research is the temperature of the system (tissue or nanoparticle suspension). Thermocouples are affordable and ubiquitous temperature sensors which could be used in this capacity; however, their metallic nature results in self-heating due to eddy currents when placed in an AMF. This presentation will quantitatively discuss calculations and measurements of the self-heating of three common types of thermocouples. Type T, K, and E thermocouples of both thin (40 gauge) and thick (20 gauge) wires were tested in a range of applied magnetic field magnitudes (235 kHz, 0-0.4 T rms). Among the thermocouples, all three types demonstrated large self-heating in 20 gauge wires. For the 40 gauge wires, type K showed large self-heating, while type T showed small but significant self-heating and type E showed no significant self-heating in comparison to the background. Our results indicate that thin type E thermocouples can be accurately used as temperature sensors in an AMF environment similar to the one used here, and type T thermocouples may be appropriate under conditions with lower magnetic field strength or frequency. [Preview Abstract] |
|
G1.00019: SEMICONDUCTORS |
|
G1.00020: Quantum Generation Dynamics of Coherent Phonon in Semiconductors: Transient and Nonlinear Fano Resonance Yohei Watanabe, Ken-ichi Hino, Muneaki Hase, Nobuya Maeshima The coherent phonon (CP) generation is one of the representative phenomena induced by ultrashort pulsed laser. In particular, in the initial stage of the CP generation in lightly $n$-doped Si, the vestige of Fano resonance (FR) manifested in a flash was observed in time-resolved spectroscopy experiments, in which it was speculated that this phenomenon results from the birth of transient polaronic quasiparticles composed of electrons and phonons strongly interacting each other [1]. This study is aimed at constructing a fully-quantum-mechanical model for the CP generation and tracking the origin of the transient FR. We calculate two physical quantities in both of polar and non-polar semiconductors such as GaAs and undoped Si. One is a retarded longitudinal susceptibility which allows one to calculate a transient induced photoemission spectrum. The other is the Fourier-transform of LO-phonon displacement into frequency domain. We have succeeded in showing that the transient FR is exclusively caused in Si in harmony with the experiments, though, not observed in GaAs [2]. [1] M. Hase, M. Kitajima, A. M. Constantinescu and H. Petek, Nature \underline {426}, 51 (2003). [2] Y. Watanabe, K. Hino, M. Hase and N. Maeshima, Phys. Rev. B (submitted), arXiv:1510.00263. [Preview Abstract] |
|
G1.00021: Transition Metal and Vacancy Defect Complexes in Phosphorene Mukul Kabir, Rohit Babar Inducing magnetic moment in otherwise nonmagnetic two-dimensional semiconducting materials is the first step to design spintronic material. Here, we study the adsorption of transition-metals on pristine and defected phosphorene, within density functional theory. We predict that increased transition-meal diffusivity on the pristine phosphorene would hinder controlled magnetism. In contrast, point-defects anchor the transiton-metal to reduce metal diffusivity. The di-vacancy complex is more important in this context due to their increased thermodynamic stability over the mono-vacancy. For most cases, the defect-transition metal complexes retain the intrinsic semiconducting properties, and induce a local moment. We provide a simple microscopic model which describe the local moment of these transition metal and defect complexes. [Preview Abstract] |
|
G1.00022: Magnetotransport in Pulsed Laser Deposited Manganese Doped Lead Sulfide Films Gaurab Rimal, Keshab Sapkota, Artur Maksymov, Leonard Spinu, Wenyong Wang, Jinke Tang Diluted magnetic semiconductors (DMS) have been proposed as promising candidates for spintronic applications. Most research in this field has been confined to III-V and II-VI semiconductor system. There are reports on IV-VI semiconductors, however reports on lead sulfide (PbS) based DMS is limited. We study the transport, magnetic and structural properties of manganese doped lead sulfide (Mn:PbS) films produced by pulsed laser deposition (PLD). The films are found to show hopping transport at low tempeature. Low temperature magnetoresistance (MR) studies show that the sign of MR can be changed by application of gate voltage. The magnetic properties of the films were also studied which showed ferromagnetic behavior at room temperature. [Preview Abstract] |
|
G1.00023: Towards thermally induced spin accumulation in Fe/GaAs structures Thomas Wagner, Kamil Olejnik, James Haigh, Andrew Irvine, Sylvain Martin, Richard Campion, Joerg Wunderlich We study non-local spin valves of semiconductor-ferromagnetic metal hybrid systems [1]. The epitaxially grown samples consist of a low doped GaAs transport channel with ultrathin Fe top contacts. Magnetic fields applied along the easy and hard axis show spin-valve and Hanle-type curves, respectively. The latter can be used to determine the spin-dephasing time in our samples [2]. We further investigate the potential of non-local spin valves for electrical detection of thermally induced spin accumulation in semiconductors. Thermal spin injection is driven by temperature gradients across interfaces between ferromagnetic and non-magnetic materials [3]. Common ways to establish the required temperature gradients are Joule heating and absorption of focused laser light. We present finite-element simulations of the temperature profile expected in our microdevices. This is of interest in the emerging field of spin caloritronics. \\ \text{[1] X. Lou \textit{et al.}, Nat. Phys. 3, 197-202 (2007)}\\ \text{[2] K. Olejn\'ik, \textit{et al.}, Phys. Rev. Lett. 109, 076601 (2012)}\\ \text{[3] A. Slachter, \textit{et al.}, Nat. Phys. 6, 879-882 (2010)} [Preview Abstract] |
|
G1.00024: Spin-orbit coupling in InSb semiconductor nanowires: physical limits for majorana states Guilherme Sipahi, Tiago de Campos, Paulo E. Faria Junior, Martin Gmitra, Igor Zutic, Jaroslav Fabian The search for Majorana fermions is a hot subject nowadays [1]. One of the possibilities for their realization is the use of semiconductor nanowires and p-type superconductors coupled together. Following this path, the first step is the determination of realistic band structures of these wires including spin-orbit effects. To consider the spin-orbit effects, its common to use models that take into account only the first conduction band. Although these reduced models have been successfully used to determine some physical properties, a more realistic description of the spin-orbit coupling between the bands is required to further investigate possible ways to realize the Majorana fermions. In this study we use a state of the art 14 band k.p formalism together with the envelope function approach [2] to determine the band structure of InAs semiconductor nanowires and analyze how the quantum confinement change the coupling between the bands. As a result we have extracted the effective masses and the spin-orbit splitting for a large range of nanowire radial sizes and for several conduction bands that can be used in effective models. [1] J. Alicea, Rep. Prog. Phys. 75, 076501 (2012). [2] P. E. Faria Junior and G. M. Sipahi, J. Appl. Phys. 10, 10, 103716 (2012). [Preview Abstract] |
|
G1.00025: Effect of magnetic polaron for acceptor bound exciton in CdTe:Dy crystals Petro Bukivskij, Yuriy Gnatenko, Anatolii Bukivskii, Roman Gamernyk We investigated low temperature (T~$=$~4.2~K) photoluminescence (PL) spectra and temperature dependence (T~$=$~1.8~-~40~K) of excitonic PL for CdTe doped by dysprosium. Dysprosium concentration was 10$^{\mathrm{20}}$ cm$^{\mathrm{-3}}$. We detected the effect of magnetic polaron for acceptor bound excitons. Theoretical analysis of temperature dependency of emission energy of these excitons was performed. The calculations based on Spalek-Deitl-Kossut theory gave us an opportunity to estimate the magnetic polaron energy $\varepsilon_{\mathrm{p}}$ and its temperature dependence $\varepsilon_{\mathrm{p}}$(T) in T~$=$~1.8 to 40~K temperature range. In addition, we calculated the temperature dependence of contributions of mean exchange field and thermodynamic fluctuations of magnetization to the spin splitting value $\Delta $. Also, we calculated the temperature dependence of probability distribution function P($\Delta $,T) of the spin splitting value for acceptor bound excitons. It was found that calculated total contributions of mean exchange field and thermodynamic fluctuations of magnetization to spin splitting value is in good agreement with experimental data. [Preview Abstract] |
|
G1.00026: Hematite nanoribbons based on (110) and (104) surfaces and their unusual character Prabath Wanaguru, Jiao An, Qiming Zhang Atomically thin hematite nanoribbons based on (110) and (104) surfaces are studied systematically by first-principles methods. Calculations have performed using the GGA$+$U approach and structures were fully relaxed to identify the geometric, electronic and magnetic properties. The studied hematite nanoribbons are formed by cutting the atomically-thin hematite nanosheets along their [100] and [010] directions. The (110) surface based nanoribbons show definite tunable semiconducting character while one type of the (104) based nanoribbons display surface modifications or bending nature indicating pseudo-Jahn-Teller effect. The remaining type of (104) based nanoribbons show built-in oxygen vacancy on one edge despite preserving the stoichiometry and introduces the half-metallicity into the nanoribbons at larger widths. We will present the optimized structures, their electronic properties and energetics in detail. [Preview Abstract] |
|
G1.00027: Optimized Energy Transfer from Electron-hole pairs to Eu ions in GaN Ruoqiao Wei, Natalie Hernandez, Brandon Mitchell, Yasufumi Fujiwara, Volkmar Dierolf Europium doped Gallium Nitride (GaN:Eu) has demonstrated potential for the red-emitting active layer in nitride-based light emitting diodes. Under above band gap excitation, the red emission was shown to increase due to the optimization of crystal growth conditions. This suggests that excitation efficiency had been improved, which would imply that the energy transfer from electron-hole pairs to Eu ions occurred on a faster time-scale. To test this assumption, we performed time-resolved spectroscopy measurements, under \emph{ps}-scale time resolution, on samples with a variety of co-dopants and growth conditions. Results show that the energy is transferred on a time scale faster than \emph{ns} and the excitation efficiency is influenced by the various growth parameters and co-dopants. [Preview Abstract] |
|
G1.00028: Free-carrier absorption from shallow donors in transparent conducting oxides Andrew Shapiro, Philip Weiser, Michael Stavola An experimental study of the free-carrier absorption in a few transparent conducting oxides (TCO's) has been performed to compare the strength of the absorption in different hosts and its dependence on wavelength and temperature. The goal of our work is to make the IR absorption arising from free carriers a quantitative tool for characterizing the conductivity of doped TCO's. [Preview Abstract] |
|
G1.00029: Structural and electronic properties of amorphous ternary and quaternary oxide semiconductors K. Nocona Sanders, Rabi Khanal, Julia E. Medvedeva Amorphous structures of several multi-cation wide-bandgap oxides (In-Ga-Zn-O, In-Sc-O, In-Y-O, and In-La-O) were obtained via first-principles molecular dynamics liquid-quench approach using different cooling rates and different oxygen and metal compositions. A detailed comparison of the structural properties, namely, the distribution of metal-oxygen (M-O) and metal-metal (M-M) distances, bond angles, and coordination, allows us to determine how the MO polyhedra network is affected by the crystalline-to-amorphous transition. Furthermore, the role of oxygen non-stoichiometry in defect formation is investigated. Specifically, local structural defects associated with severe distortions in the metal-oxygen polyhedra, such as under-coordinated metal and oxygen atoms, or M-M bonds, appear in the electronic band structure of amorphous oxides. Both carrier-generating defects and carrier trapping/scattering defects are identified. The results help determine the optimal composition and preparation conditions (i.e., oxygen partial pressure, deposition temperature) in order to achieve the desired properties of the technologically-appealing amorphous oxide semiconductors. [Preview Abstract] |
|
G1.00030: Anomalous Magneto-Optical Behavior of Rare Earth Doped Gallium Nitride Andrew Helbers, Brandon Mitchell, Nathaniel Woodward, Volkmar Dierolf We have observed unusual magneto-optical properties in rare earth doped gallium nitride. Specifically, the reversal of a magnetic field applied parallel to the c-axis produces unexpected, marked differences in luminescence spectra in several of our samples. Notably, relative emission strengths of Zeeman-split lines from the rare earth ions appear to change when the field is reversed. These effects were not observed in rare earth doped lithium niobate and lithium tantalate, which are also hexagonal and polar. Measurements for erbium doped gallium nitride suggest that these asymmetries seem to be linked to the degree of ferromagnetism of the samples. Results are presented showing these differences. The symmetry of the observed effects requires a perturbation of the RE states with a screw like symmetry. We explore whether this may be accomplished by defects such as threading dislocations. [Preview Abstract] |
|
G1.00031: Optical and Electrical Studies of Gamma-Irradiated AlGaN/GaN High Electron Mobility Transistors Anupama Yadav, Elena Flitsiyan, Leonid Chernyak, Shihyun Ahn, Fan Ren, Stephen Pearton, Igor Lubomirsky, Sergey Khodorov The impact of $^{\mathrm{60}}$Co gamma-irradiation on n-channel AlGaN/GaN High Electron Mobility Transistors (HEMTs) was studied by means of temperature dependent Cathodoluminescence (CL) and Electron Beam Induced Current (EBIC) technique. Increase in diffusion length after low dose of gamma-irradiation ($\le $ 200 Gy) is consistent with the decrease in the CL intensity. The observed effect is explained via the mechanism involving trapping of Compton electrons on irradiation induced nitrogen vacancies. For high dose (\textgreater 200 Gy), diffusion length was observed to decrease which is presumably associated with the mobility degradation. It is shown that calculated activation from the EBIC and CL measurements follows exactly the same trend, which implies that same underlying phenomenon is responsible for observed findings. In addition, DC current-voltage measurements were conducted on the devices in order to relate the material's fundamental properties to the device performance. [Preview Abstract] |
|
G1.00032: Computational modelling of the Li effects on the electronic structure of porous silicon Mar\'Ia Lucero Gomez-Herrera, \'Alvaro Miranda Dur\'an, Alejandro Trejo Ba\~nos, Miguel Cruz Irisson This work analyses the effects of Li impurities on the electronic structure of pSi by means of the density functional theory with the generalized gradient approximation and the supercell scheme. The porous structures were modeled by removing atoms in the [001] direction of an otherwise perfect Si crystal. All surface dangling bonds were saturated with H atoms. To model the Li impurities some H atoms are replaced with Li atoms at the surface. Results show additional bands around the Fermi level with the insertion of a single Li atom on the pore surface, which suggests a trap-like state of localized charge. With increasing concentration of surface Li the band gap gradually decreases approaching to a metallic behavior. This results could be important to the application of pSi in Li-ion batteries [Preview Abstract] |
|
G1.00033: Tuning the electronic band-gap of fluorinated 3C-silicon carbide nanowires \'Alvaro Miranda Dur\'an, Alejandro Trejo Ba\~nos, Luis Antonio P\'erez, Miguel Cruz Irisson The possibility of control and modulation of the electronic properties of silicon carbide nanowires (SiCNWs) by varying the wire diameter is well known. SiCNWs are particularly interesting and technologically important, due to its electrical and mechanical properties, allowing the development of materials with specific electronic features for the design of stable and robust electronic devices. Tuning the band gap by chemical surface passivation constitutes a way for the modification of the electronic band gap of these nanowires. We present, the structural and electronic properties of fluorinated SiCNWs, grown along the [111] crystallographic direction, which are investigated by first principles. We consider nanowires with six diameters, varying from 0.35 nm to 2.13 nm, and eight random covering schemes including fully hydrogen- and fluorine terminated ones. Gibbs free energy of formation and electronic properties were calculated for the different surface functionalization schemes and diameters considered. The results indicate that the stability and band gap of SiCNWs can be tuned by surface passivation with fluorine atoms [Preview Abstract] |
|
G1.00034: Excitonic photoluminescence lifetimes in PbI2 nanoclusters for PbCdI2 semiconductor materials Anatolii Bukivskii, Yuriy Gnatenko, Yuri Piryatinski We investigated excitonic photoluminescence (PL) spectra and kinetics of PL decays for various wavelengths for Pb$_{\mathrm{1-X}}$Cd$_{\mathrm{X}}$I$_{\mathrm{2}}$ solid solutions (X~$=$~0.2, X~$=$~0.3, X~$=$~0.4, X~$=$~0.5, X~$=$~0.7). Earlier we had shown that by approximation of the experimental data with stretched exponential function and applying the inverse Laplace transformation to this function we can estimate the average time constant \textless $\tau $\textgreater of the PL decay. Now, instead of measuring single kinetics for several wavelengths, we performed Time Resolved Emission Scanning continuously for all of the self-trapped excitons emission ranges. We developed analytical software that enables us to calculate both the average time constant \textless $\tau $\textgreater of the decay and average lifetime $\tau $ of the emission process. This software also enables us to calculate distribution of rate constants $H(k) $for each concentration for each wavelength. By using the demo version of Edinburgh Instruments FAST software, we also calculated continuous distribution of time constants of PL kinetics in Pb$_{\mathrm{1-X}}$Cd$_{\mathrm{X}}$I$_{\mathrm{2}}$ solid solutions. These distributions show the presence of three different components of the PL signal, which are time-separated. These results strongly correlate with obtained spectral data. [Preview Abstract] |
|
G1.00035: Evidence of iridescence in TiO$_2$ nanostructures. A probably photonic effect Rafael Rey-Gonzalez, Heiddy P. Quiroz, Claudia Barrera-Patiño, Anderson Dussan In this work, we present a study of optical properties of titanium dioxide nanotubes (TiO$_2$). Nanotubes were obtained by electrochemical anodization method, using ethylene glycol solutions containing different amounts of water and fluoride. A complex structure is observed between nanotubes and Ti foils on surface when nanotubes are released from the sheet. These forms can be associated with replicas or marks in surface of the Ti foil. The optical response of replicas is studied by Uv-Vis spectrophotometry using white light and varying the angle of the incident light. Absorbance measurements reveal that these replicas exhibit a shift towards lower values of lambda when the angle of the incident light increases of 20$^0$ to 60$^0$. These changes may be associated with iridescent effects in this material. The concavity of the replicas in association with air could be generating photonic-like effects. Using a 2D model of replicas - air system, the photonic band structures are found through a plane wave approach. Correlations between photonic properties and iridescent effects are explored. [Preview Abstract] |
|
G1.00036: ABSTRACT MOVED TO L29.00015 |
|
G1.00037: ABSTRACT WITHDRAWN |
|
G1.00038: Simple Screened Hydrogen Model of Excitons in Two-Dimensional Materials Thomas Olsen, Simone Latini, Filip Rasmussen, Kristian Thygesen We present a generalized hydrogen model for the binding energies ($E_B$) of excitons in two-dimensional (2D) materials that sheds light on the fundamental differences between excitons in two and three dimensions. In contrast to the well-known hydrogen model of three-dimensional (3D) excitons, the description of 2D excitons is complicated by the fact that the screening cannot be assumed to be local. We show that one can consistently define an effective 2D dielectric constant by averaging the screening over the extend of the exciton. For an ideal 2D semiconductor this leads to a simple expression for $E_B$ that only depends on the excitonic mass and the 2D polarizability $\alpha$. The model is shown to produce accurate results for 51 transition metal dichalcogenides. Remarkably, over a wide range of polarizabilities the expression becomes independent of the mass and we obtain $E^{2D}_B\approx3/(4\pi\alpha)$, which explains the recently observed linear scaling of exciton binding energies with band gap. It is also shown that the model accurately reproduces the non-hydrogenic Rydberg series in WS$_2$ and can account for screening from the environment. [Preview Abstract] |
|
G1.00039: Measurement of Exciton Binding Energy of Monolayer WS$_{\mathrm{2}}$ Xi Chen, Bairen Zhu, Xiaodong Cui Excitonic effects are prominent in monolayer crystal of transition metal dichalcogenides (TMDCs) because of spatial confinement and reduced Coulomb screening. Here we use linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE) to measure the exciton binding energy of monolayer WS$_{\mathrm{2}}$. Peaks for excitonic absorptions of the direct gap located at K valley of the Brillouin zone and transitions from multiple points near $\Gamma $ point of the Brillouin zone, as well as trion side band are shown in the linear absorption spectra of WS$_{\mathrm{2}}$. But there is no gap between distinct excitons and the continuum of the interband transitions. Strong electron-phonon scattering, overlap of excitons around $\Gamma $ point and the transfer of the oscillator strength from interband continuum to exciton states make it difficult to resolve the electronic interband transition edge even down to 10K. The gap between excited states of the band-edge exciton and the single-particle band is probed by TP-PLE measurements. And the energy difference between 1s exciton and the single-particle gap gives the exciton binding energy of monolayer WS$_{\mathrm{2}}$ to be about 0.71eV. [Preview Abstract] |
|
G1.00040: ABSTRACT WITHDRAWN |
|
G1.00041: ABSTRACT WITHDRAWN |
|
G1.00042: Metal to insulator quantum-phase transition in few-layered ReS}$_{\mathbf{2}}$. Nihar Pradhan, Daniel Rhodes, Zhenguang Lu, Dmitry Smirnov, Efstratios Manousakis, Vladimir Dobrosavljevic, Luis Balicas, Amber McCreary, Simin Feng, Maurico Terrones, Raju Namburu, Madan Dubey, Angela Hight Walker, Humberto Terrones ReS$_{2}$ a layer-independent direct band-gap semiconductor of 1.5 eV implies a potential for its use in optoelectronic applications. Here, we present an overall evaluation of transport and anisotropic Raman of few-layered ReS$_{2}$ FET. ReS$_{2}$ exfoliated on SiO$_{2}$ behaves as an $n$-type semiconductor with an intrinsic carrier mobility surpassing $\mu _{i}$ \textasciitilde 30 cm$^{2}$/Vs at $T =$ 300 K which increases up to \textasciitilde 350 cm$^{2}$/vs at 2 K. Semiconducting behavior is observed at low electron densities $n$, but at high values of $n $the resistivity decreases by a factor \textgreater 7 upon cooling to 2 K and displays a metallic$^{\, }T^{2}$-dependence. The electric-field induced metallic state observed in MoS$_{2}$ was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of $T $and $n$, we find that the metallic state of ReS$_{2}$ results from a second-order metal to insulator transition driven by electronic correlations. [Preview Abstract] |
|
G1.00043: Finite two-dimensional electron gas in a patterned semiconductor system Orion Ciftja, Victoria Livingston, Elsa Thomas, Seth Saganti On various occasions, fabrication of a two-dimensional semiconductor quantum dot leads to a small system of electrons confined in a domain that is not circular and may have a pronounced square (or rectangular) shape. In this work we consider a square-shaped semiconductor quantum dot configuration and treat the system of electrons as a finite two-dimensional electron gas. Within this framework, we adopt a Hartree-Fock approach and study the properties of a small two-dimensional system of electrons confined in a finite square region. We calculate the energy for various finite systems of fully spin-polarized (spinless) electrons interacting with a Coulomb potential. The results give a fairly accurate picture of how the energy of the finite system evolves towards the bulk value as the size of the system increases. The calculations for a square domain are challenging since expressions depend in each component of particle's position and not the radial distance from the center of the square-shaped semiconductor quantum dot. Therefore, we also consider a possible circularly symmetric approximation to the problem. We assess the quality of this approximation and discuss instances where its use is not only desirable, but also accurate. [Preview Abstract] |
|
G1.00044: Strain Engineered Direct-indirect Band Gap Transition and its Mechanism in 2D Phosphorene. Xihong Peng, Qun Wei, Andrew Copple Phosphorene, a two-dimensional puckered honeycomb structure of black phosphorus, showed promising properties for applications in nano-electronics. In this work, we report strain effect on the electronic band structure of phosphorene, using first principles density-functional theory (DFT) including standard DFT and hybrid functional methods. It was found that phosphorene can withstand a tensile strain up to 30{\%}. The band gap of phosphorene experiences a direct-indirect-direct transition when axial strain is applied. The origin of the gap transition was revealed and a general mechanism was developed to explain energy shifts with strain according to the bond nature of near-band-edge electronic orbitals. Effective masses of carriers in the armchair direction are an order of magnitude smaller than that of the zigzag axis indicating the armchair direction is favored for carrier transport. Ref: X.-H. Peng, Qun Wei,~A. Copple, Phys. Rev. B 90, 085402 (2014).~ [Preview Abstract] |
|
G1.00045: STM study on the structures of SnSe surfaces Tae Hoon Kim, Sang-ui Kim, Trinh Thi Ly, Anh Tuan Duong, Sunglae Cho, S. H. Rhim, Jungdae Kim SnSe is a 2 dimensional layered material, and each layer is coupled by van deer Waals forces allowing very easy cleaving though the layer surfaces. SnSe has been studied for various potential applications because of its high stability and elemental abundance in earth. Recently, it was also reported that bulk SnSe has an excellent thermoelectric property of ZT$=$2.6 at 923 K along the b axis (Zhao et al, Nature 508 373 (2014)). The surface of a single crystal SnSe was studied via a home-built low temperature scanning tunneling microscopy (STM). Clear atomic images of SnSe surfaces were observed at the filled and empty state measurements, and detail atomic structures were analyzed by comparing with DFT simulations. We found that the atomic image of SnSe surfaces measured by STM is not trivial to understand. Only Sn atoms were visible on STM topographic images for the both of filled and empty state probing. [Preview Abstract] |
|
G1.00046: STM study on the surface defects of SnSe induced by thermal annealing Trinh Thi Ly, Sang-ui Kim, Tae Hoon Kim, Anh Tuan Duong, Sunglae Cho, S. H. Rhim, Jungdae Kim SnSe is a IV - VI semiconductor with 0.86 eV gap, and a single crystal SnSe usually exhibits a p-type characteristic. SnSe is one of 2D layered materials, and it has attracted researchers' attentions due to excellent physical properties for future applications. In particular, exceptionally high ZT value (ZT $=$ \textasciitilde 2.6 at 923 K) was reported for SnSe single crystal (Zhao \textit{et al}, Nature \textbf{508} 373 (2014)). Even though many researches on SnSe have proposed the possibilities of various applications so far, surprisingly little information is available regarding the microscopic structure of SnSe surfaces. We conducted a systematic study on the surface defect of SnSe induced by thermal annealing via a home-built low temperature scanning tunneling microscopy (STM). Various defects were characterized by STM/STS, and we found that Sn vacancy is a dominating intrinsic defect. The size of vacancy was changed after annealing process in UHV at different temperatures. [Preview Abstract] |
(Author Not Attending)
|
G1.00047: Polarization-dependent photocurrents in polar stacks of van der Waals solids Songci Li, Yuli Lyanda-Geller, Anton Andreev Monolayers of semiconducting van der Waals solids, such as transition metal dichalcogenides (TMDs ),acquire significant electric polarization normal to the layers when placed on a substrate or in a heterogeneous stack. This causes linear coupling of electrons to electric fields normal to the layers. Irradiation at oblique incidence at frequencies above the gap causes interband transitions due to coupling to both normal and in-plane ac electric fields. The interference between the two processes leads to sizable in-plane photocurrents and valley currents. The direction and magnitude of currents is controlled by light polarization and is determined by its helical or nonhelical components. The helicity-dependent ballistic current arises due to asymmetric photo generation. The non-helical current has a ballistic contribution (dominant in sufficiently clean samples) caused by asymmetric scattering of photoexcited carriers, and a side-jump contribution. Magneto-induced photocurrent is due to the Lorentz force or due to intrinsic magnetic moment related to Berry curvature. [Preview Abstract] |
|
G1.00048: Anisotropic diffusion of oxygen on a few layers of black phosphorous. Hector Noe Fernández-Escamilla, Víctor Hugo González-Chávez, Eduardo Martínez-Guerra, Andrés Garay-Tapia, Edgar Martínez-Guerra Recently, phosporene has also been scored well as a functional material for two-dimensional electronic and optoelectronic devices. That is, because in contrast to graphene, black phosphorous has an inherent, direct and appreciable band gap that can be modulated with the numbers of layes. However, the presence of exposed lone pairs at the surface makes phosphorous very reactive to air and humidity and consequently, degradation of its properties. No such fundamental explanation have been made, thus corresponding first principle predictions to evaluate diffusion of O over and along a mono- and a few layers are indispensable. Energy barriers and the mechanisms of oxygen diffusion on mono- and a few layer of black phosphorous were calculated using the NEB(Nudge Elastic band) method as implemented in Quantum Espresso. The electronic states are expanded in plane waves with kinetic-energy cutoffs of 25 and 200 Ry for the wave function and charge density, respectively. Also, as the H$_{\mathrm{2}}$O and O$_{\mathrm{2\thinspace }}$are polar molecules, spin-polarized calculations have been carried out. We evaluated the diffusion barriers for O$_{\mathrm{2\thinspace }}$and H$_{\mathrm{2}}$O on phosphorene along zigzag, armchair and intermediated directions. Our calculations show that diffusion of O is preferred on zigzag directions and dissociation of O$_{\mathrm{2}}$ is favored as a result of energy gains of about 2 eV. Also, apparently diffusion pathways are blocked along layers. [Preview Abstract] |
|
G1.00049: Effect of the electric field on buckled and puckered arsenene. Victor Hugo Chavez, Hector Noe Fernandez-Escamilla, Edgar Martínez-Guerra With the emergence of new 2D materials, more recently phosphorene, arsenene appears as a new candidate to be explored for electronic devices. We have studied the stability of arsenene pristine and the effect of a transversal electric field on its electronic properties. The calculations were performed using the SIESTA code, with the GGA exchange-correlation functional in the PBE form. We have used numerical atomic orbitals as the basis set for the valence wavefunctions employing a double $\zeta $-polarized basis. We use the Perdew-Becke pseudopotential for an As atom that includes the scalar-relativistic effect and Troullier-Martins parametrization. We adopt the Monkhorst-Pack scheme for k-point sampling of Brillouin zone integrations with 25 \texttimes 25 \texttimes 1 and 25 \texttimes 25 \texttimes 1 for the buckled/planar and puckered systems, respectively. We found that buckled and puckered arsenenes are stable and posses indirect gap. The effect of the electric field on the electronic structure of the buckled arsenene is the modulation of indirect to direct gap, while in puckered arsenene the gap linearly decreases as electric field is increased. This research was supported by Consejo Nacional de Ciencia y Tecnolog\'{\i}a (Conacyt) under Grant No. 43830-F. [Preview Abstract] |
|
G1.00050: ABSTRACT WITHDRAWN |
|
G1.00051: ABSTRACT WITHDRAWN |
|
G1.00052: A theoretical study on the thermal oxidation of silicon carbide: Chemical species at the SiO$_{\mathrm{2}}$/SiC interface Nobuo Tajima, Tomoaki Kaneko, Jun Nara, Takahiro Yamasaki, Tatsuo Schimizu, Koichi Kato, Takahisa Ohno Silicon carbide (SiC) is potentially a suitable candidate of the channel materials of power devices since it has wide bandgap, high electron mobility, and thermal conductivity. Furthermore, it is favorable for device fabrication as it can be thermally oxidized to create insulating silicon oxide (SiO$_{\mathrm{2}})$ layer. However, the SiC devices of current technology do not show acceptable performance because of a defective nature of the created SiO$_{\mathrm{2}}$/SiC stacking structure, which causes problems such as channel mobility degradation, threshold voltage increase, and leakage current. The origins of the defective nature are not understood so far, though it is presumed that they are rather concentrated at the interface. In the present study, we have performed first principles calculations to know the chemical species possibly produced at the oxide interface of thermally oxidized SiC. The First principles simulation code PHASE/0 (\underline {http://www.ciss.iis.u-tokyo.ac.jp/riss/english/project/device/}) was used in the theoretical calculations. [Preview Abstract] |
|
G1.00053: Preparation and study of Titanium Nitride films by reactive sputtering and an investigation of target poisoning during the process. Tareque Aziz, Abdul Rumaiz Titanium Nitride (TiN$_{\mathrm{x}})_{\mathrm{\thinspace }}$thin films were prepared by reactive dc sputtering in presence of Ar-N$_{\mathrm{2}}$ plasma. The thin films were grown on Quartz and pure Si surfaces. The Ar-N$_{\mathrm{2}}$ content ratio was gradually varied while the substrate and the Titanium target were kept at room temperature. Structural properties, optical and electrical properties of the thin films were studied by using X-ray Photoelectron Spectroscopy (XPS) and XRD and 4 probe resistivity measurement. Target poisoning of the Ti target was also studied by varying reactive gas concentration and measuring the target current. A study of target current vs growth rate of the films was performed to investigate the onset of ``poison'' mode\textbf{. }Although there was an insignificant drop in plasma current, we noticed a drop in the deposition rate. This result was tested against Monte Carlo simulations using SRIM simulations. Effects of annealing on the crystallinity and the sheet resistance will also be discussed. [Preview Abstract] |
|
G1.00054: Optimization of metamorphic buffers for molecular epitaxial growth of high quality AlInSb/InSb quantum structures Yinqiu Shi, Denise Gosselink, Kaveh Gharavi, Jonathan Baugh, Zbigniew Wasilewski Strong spin-orbit interaction in InSb quantum wells and wires makes them attractive candidates for the realization of Majorana bound states. Molecular beam epitaxy (MBE) is the best tool to obtain these structures but lack of suitable substrates demands development of low dislocation density, smooth metamorphic buffer layers, lattice matched to the InAlSb/InSb material system. Here we present a comparative study of MBE growth of such buffers on GaAs substrates oriented in [001] crystallographic direction and [001] offcut 2$^{\circ}$ towards [100]. 1$\mu$m-thick AlSb nucleation buffers were grown on both substrates with optimized growth conditions. The high density of surface terraces on the offcut substrates effectively suppressed the formation of undesirable hillocks, typical of growth on [100] substrates. Further lattice constant grading and dislocation filtering was achieved through repetitions of Al$_{0.24}$In$_{0.76}$Sb interlayers in the Al$_{0.12}$In$_{0.88}$Sb matrix. Surface morphology evolved quite differently through these stages of metamorphic buffer preparation on both types of substrates, resulting in up to 50nm-high hillocks for the on-orientation substrates and hillock-free morphology for 2$^{\circ}$ off substrates. Mechanism of hillock suppression is discussed. [Preview Abstract] |
|
G1.00055: Epitaxial aluminum on hybridized InAs/GaSb quantum wells Bing-Bing Tong, Ting-Xin Li, Xiao-Yang Mu, Chi Zhang, Rui-Rui Du Hybridized InAs/GaSb quantum wells (QW) are approved the existence of helical edge channels. According to the theoretical prediction, the combination with superconductor will lead to superconducting topological phase and realization of Majorana bound state (MBS). Besides, InAs/GaSb material shows a low Schottky barrier to superconductor, and high quality of superconductor-topological insulator interface will result in hard induced gap. In recent report [1], under low temperature of substrate, there is a good lattice match between InAs naowire and Al in the same direction. In our lab, we perform aluminum epitaxy on the in-situ cleaved InAs/GaSb QW with similar methods in our ultra-high vacuum STM system. After metal epitaxy, the Al layer can be selectively etched for fabricating the superconductor-topological insulator junction devices. [1] P. Krogstrup, N. L. B. Ziino, W. Chang, S. M. Albrecht, M. H. Madsen, E. Johnson, J. Nyg{\aa}rd, C. M. Marcus, T. S. Jespersen, Nature Materials 14, 400 (2015). [Preview Abstract] |
|
G1.00056: Synthesis and Analysis of MnTiO3 Thin Films on ITO Coated Glass Substrates Emerick Martin, Mehmet-Alper Sahiner Perovskites like Manganese Titanium Oxide have interesting chemical properties that may be advantageous to the development of p-n junction photovoltaic cells. Due to the limited understanding behind the compound, it is essential to know the characteristics of it when it is deposited in thin film form. The cells were created using pulsed laser deposition method for two separate mediums (first layers after ITO). ZnO was deposited onto ITO glass for the first sample. For the second sample, a layer of pure Molybdenum was deposited onto the ITO glass. The MnTiO3 was then deposited onto both samples. There was a target thickness of 1000 Angstroms, but ellipsometry shows that, for the Mo based sample, that film thickness was around 1500 Angstroms. There were inconclusive results for the ZnO based sample. The concentration of active carriers was measured using a Hall Effect apparatus for the Mo based sample. The XRD analyses were used to confirm the perovskite structure of the films. Measurements for photoelectric conversion efficiency were taken using a Keathley 2602 ScourceMeter indicated low values for efficiency. The structural information that is correlated with the low electrical performance of this sample will be discussed. [Preview Abstract] |
|
G1.00057: The Study of the Thermoelectric Properties of Phase Change Materials Ming Yin, Mohammed Abdi, Zibusisu Noimande, Godwin Mbamalu, Dheyaa Alameeri, Timir Datta We study thermoelectric property that is electrical phenomena occurring in conjunction with the flow of heat of phase-change materials (PCM) in particular GeSbTe (GST225). From given sets of material parameters, COMSOL Multiphysics heat-transfer module is used to compute maps of temperature and voltage distribution in the PCM samples. These results are used to design an apparatus including the variable temperature sample holder set up. An Arbitrary/ Function generator and a circuit setup is also designed to control the alternation of heaters embedded on the sample holder in order to ensure sequential back and forward flow of heat current from both sides of the sample. Accurate values of potential differences and temperature distribution profiles are obtained in order to compute the Seebeck coefficient of the sample. The results of elemental analysis and imaging studies such as XRD, UV-VIS, EDEX and SEM of the sample are obtained. Factors affecting the thermoelectric properties of phase change memory are also discussed. [Preview Abstract] |
|
G1.00058: Electron Density and Capacitance at the interface of Au-ZnO Based Schottky Diode Chin-sheng Wu ZnO with wide direct band gap (3.37 eV) is a well-known and an interesting compound semiconducting material, which have been used for the fabrication of optical, electrical, and piezoelectric devices such as light emitting diodes, solar cells. Schottky diodes are associated with quicker switching and lower turn on voltages compared to p--n junction diodes. J--V characteristics exhibit nonlinear rectifying behavior with threshold voltage of 2.1 V. The barrier heights were found to be 0.61 eV. The measured capacitance for the Schottky junction depends on the reverse bias potential and frequency. At the lower frequencies the capacitance has the higher values due to the trapping occurred at the interface through the surface roughness and lattice mismatch. We perform model potential calculation with quantum well around the interface. Model potentials allow some degree of freedom in the design of the emitted wavelength through adjustment of the energy levels. We apply the various well width w and barrier height V in order to match the device information made by Willander. Solving the Schrödinger equation with exchange- correlation energy and effective mass of electrons will produce values of the energy levels and states. The variational barrier heights result in the change of the electron density This accounts for the excessive capacitance at the interface of Schottky diode. [Preview Abstract] |
|
G1.00059: Electronic structure and magnetism in partially gated graphene nano-ribbons RITA MAJI, JOYDEEP BHATTACHARJEE Properties of 3-coordinated carbon networks evolve upon physical or chemical functionalization depending on the resultant modification to $\pi$-conjugation and its interplay with the anti-ferromagnetic(AFM) correlation between unpaired 2$p_z$ electrons at nearest neighbor(nn) sites. Although the former generally dominates the latter in determining the ground state, we propose it to be possible to enhance and modify nn magnetic correlations by inducing non-uniform density of electrons through application of bias partially within a periodic unit. Using tight-binding based mean-field Hubbard model and the DFT based first principles calculations, we show in ZGNRs as well as AGNRs, a systematic emergence of nn ferromagnetic(FM) correlation and spin-separation within and in the vicinity of positively biased region in a unit-cell, as an intermediate phase, as the ground state evolves from AFM to non-magnetic as a function of bias voltage. The associated evolution of the degenerate band-structure from direct to indirect is also punctuated by lifting of degeneracy coinciding exactly with the appearance of nn FM correlation and accommodating energy windows for half-metallic transport. In ZGNR such localization driven nn FM correlation leads to non-trivial edge magnetism and band-structure. [Preview Abstract] |
|
G1.00060: Effective multiband Hamiltonian for InAs in wurtzite phase Paulo E. Faria Junior, Tiago Campos, Carlos M. O. Bastos, Guilherme M. Sipahi, Martin Gmitra, Jaroslav Fabian Recent advances in nanostructure growth techniques allowed the synthesis of new III-V compounds with wurtzite crystal structure[1]. Although ab initio band structures for these new wurtzite materials can be found in the literature[2], we still lack multiband models and parameter sets that can be simply used to investigate, for instance, quantum confinement effects. In this study, we calculated the ab initio band structure of bulk InAs wurtzite and developed a multiband k.p Hamiltonian to describe the energy bands around the energy gap. In order to correctly describe the spin splitting effects we included the k-dependent spin-orbit term, often neglected in literature. We showed that our model is very robust to describe the important features of the band structure and also the spin splittings with great agreement to the ab initio values. [1] P. Caroff et al., Nat. Nanotechnol. 4, 50 (2009). [2] A. De and C. E. Pryor, PRB 81, 155210 (2010). [Preview Abstract] |
|
G1.00061: Magneto-Electronic Energy Spectra of Monolayer Tinene S. C. Chen, F. L. Shyu, J. Y. Wu, C. W. Chiu, C.H. Lee, M. F. Lin The novel magnetic quantization in monolayer tinene, being closely related to the sp$^{\mathrm{3}}$ bondings, spin-orbital coupling and magnetic field, is investigated by the generalized tight-binding model. The feature-rich two groups of low-lying LLs, which are, respectively, dominated by the 2p$_{\mathrm{z}}$ orbitals and (2p$_{\mathrm{x}}$,2p$_{\mathrm{y}})$ orbitals, are revealed near the Fermi level simultaneously. They are very different in the spatial distributions, state degeneracy, spin configurations and B$_{\mathrm{z}}$-dependence. The B$_{\mathrm{z}}$-dependent energy spectra might be approximated by the simple relationships. The splittings of LLs in the second groups are due the effects of magnetic fields. The unique magnetic-electronic properties in tinene are absent in graphene, silicene and germanene. The predicted magneto-electronic energy spectra could be directly verified by the STS measurements. [Preview Abstract] |
|
G1.00062: Ab-Initio Computations of Electronic and Related Properties of cubic Lithium Selenide (Li$_{2}$Se) Abdoulaye Goita, Ifeanyi H. Nwigboji, Yuriy Malozovsky, Diola Bagayoko We present theoretical predictions, from ab-initio, self-consistent calculations, of electronic and related properties of cubic lithium selenide (Li$_{2}$Se). We employed a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). We performed the computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Our results include electronic energies, total and partial densities of states, effective masses, and the bulk modulus. The theoretical equilibrium lattice constant is 5.882 {\AA}. We found cubic Li$_{2}$Se to have a direct band gap of 4.363 eV (prediction), at $\Gamma $. This gap is 4.065 eV for a room temperature lattice constant of 6.017 {\AA}. The calculated bulk modulus is 31.377 GPa. Acknowledgments: This work was funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR] and NSF HRD-1002541, the US Department of Energy -- National, Nuclear Security Administration (NNSA) (Award No. DE- NA0002630), LaSPACE, and LONI-SUBR. [Preview Abstract] |
|
G1.00063: Ab-initio Density Functional Theory (DFT) Studies of Electronic, Transport, and Bulk Properties of Sodium Oxide (Na$_{2}$O). Daniel Polin, Joshua Ziegler, Yuriy Malozovsky, Diola Bagayoko We present the findings of \textit{ab-initio} calculations of electronic, transport, and structural properties of cubic sodium oxide (Na$_{2}$O). These results were obtained using density functional theory (DFT), specifically a local density approximation (LDA) potential, and the linear combination of Gaussian orbitals (LCGO). Our implementation of LCGO followed the Bagayoko, Zhao, and Williams method as enhanced by the work of Ekuma and Franklin (BZW-EF). We describe the electronic band structure of Na$_{2}$O with a direct band gap of 2.22 eV. Our results include predicted values for the electronic band structure and associated energy eigenvalues, the total and partial density of states (DOS and pDOS), the equilibrium lattice constant of Na$_{2}$O, and the bulk modulus. We have also calculated the electron and holes effective masses in the $\Gamma $ to L, $\Gamma $ to X, and $\Gamma $ to K directions. Acknowledgments: This work was funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR] and NSF HRD-1002541, the US Department of Energy -- National, Nuclear Security Administration (NNSA) (Award No. DE- NA0002630), LaSPACE, and LONI-SUBR. [Preview Abstract] |
|
G1.00064: Auger recombination in InGaN/GaN Chi-Chan Huang, Wen-Ching Chao, Wei-Sheng Chen, Antaryami Mohanta, Der-Jun Jang The radiative and nonradiative recombination of InGaN/GaN samples were studied by time-resolved photoluminescence apparatus and time-integrated photoluminescence by photoexcitation with laser pulses of temporal resolution of 100 ps and energies of 3.0 and 4.5 eV. We found that the Shockley-Read-Hall and Auger coefficients derived from the analysis of TRPL using the rate equation of carrier concentration were much larger than those derived from the time-integrated PL photoexcited with various numbers of carrier concentration. We will discuss the discrepancy. [Preview Abstract] |
|
G1.00065: Effect of GaAs spacer layer thickness on optical properties of multi-stacked InAs/GaAs quantum dots Chia-Hsiang Wang, Antaryami Mohanta, Der-Jun Jang, Fu-Yu Wang, J. S. Wang Effect of GaAs spacer layer thickness ($d_{\mathrm{GaAs}})$ on multi-stacked InAs/GaAs quantum dots are investigated by photoluminescence (PL) and excitation wavelength ($\lambda_{\mathrm{exc}})$ dependent pump-probe reflection spectroscopy. Dominance of light hole transition in the PL spectra is observed at smaller $d_{\mathrm{GaAs}} $(\textless 15 nm). Double maxima ($\Delta $R/R)$_{\mathrm{1}}$ and ($\Delta $R/R)$_{\mathrm{2}}$ appear in the differential reflection spectra (DRS) at intermediate $\lambda _{\mathrm{exc}}$ beyond which positive to negative reversal of the DRS is observed due to dominating effect of inter band absorption in InAs wetting layer. The $\lambda_{\mathrm{exc}}$ at which double maxima occur, and the positive to negative reversal starts is found to be dependent on $d_{\mathrm{GaAs}}$ [Preview Abstract] |
|
G1.00066: Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure Wen-Ching Chao, Antaryami Mohanta, Tsu-Chiang Yen, Wei-Sheng Chen, Der-Jun Jang Green emitting InGaN/GaN multi-quantum well samples were investigated using photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of \textasciitilde 12 meV due to an inhomogeneous distribution of In in the InGaN quantum well (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum (FWHM) of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, $\tau_{\mathrm{r}}$, extracted from the TRPL profile shows \textasciitilde $T^{\mathrm{3/2}}$ dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature. [Preview Abstract] |
|
G1.00067: The carrier recombination in ZnO/Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ superlattice Ko Mai, Wei-Sheng Chen, Tsu-Chiang Yen, Der-Jun Jang, Yung-Sung Chen The optical properties of ZnO/Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ superlattice are studied by a time-correlated single-photon counting apparatus with temporal resolution of 150 ps using laser pulses of energy 4.5 eV from a Ti:sapphire laser. Photoluminescence emission around 550 nm is clear evident for photoexcitation with energies of 3.0 and 4.5 eV. The differences of the widths of the PL spectrum and lifetimes of carrier recombination are compared for both photoexcitation and are explained by the spatial overlap of the carriers inside the superlattices [Preview Abstract] |
|
G1.00068: Quantum Interference, Geometric-phase Effects, and Semiclassical Transport in Quantum Hall Systems at Low Magnetic Fields Chun-feng Huang, I.-H. Tsai It is well-established how the quantum interference induces strong localization leading to quantum Hall effect at high enough magnetic fields. Decreasing the magnetic fields, however, the localization strength can be reduced and the semiclassical magneto-oscillations following Shubnikov-de Haas formula appear in most quantum Hall systems. To understand the transport properties as the localization strength becomes weak, our team has investigated the magneto-resistance in some quantum Hall systems at low magnetic fields. Under the semiclassical transport, the crossing points in Hall plateaus showed Landau-band quantization and microwave-induced heating demonstrated the band-edge equivalence important to Landau-level addition transformation [1-2]. We note that such equivalence is consistent with the edge universality based on the random matrices of Wigner type, and the Landau-band quantization can be explained by considering geometric phase effects. From our study, some quantum Hall features can survive as the semiclassical transport reveals the insufficient localization. [1] Solid State Commun. 141, 17 (2007). [2] Solid State Commun. 156, 45 (2013). [Preview Abstract] |
|
G1.00069: Stability of composite fermion states in Chern insulators Pawel Potasz, Blazej Jaworowski We analyze an existence of composite fermion (CF) states in fractional Chern insulators (FCI) using exact diagonalization. The consider Chern insulator models for spinless fermions exhibit a signature of CF states at 2/5 and 3/7 filling factors. Evidences of fractional quantum Hall type phases for a region in a parameter space with larger energy gap are shown by looking at momenta of the n-fold degenerate ground state, spectral flow, quasihole excitation spectrum, and entanglement spectra. We analyze stability of phases as a function of model parameters showing strong correlation with flatness of Berry curvature. [Preview Abstract] |
|
G1.00070: Multi-state magnetoresistance in ferromagnet/organic-ferromagnet/ferromagnet junctions. Guichao Hu, Shijie Xie Organic ferromagnets (OFs) are fascinating in the field of organic spintronics, since they combine both the ferromagnetic and organic properties. The utilization of OFs in the design of organic spintronic is promising to generate some novel effects [1-4]. Here, we designed an organic spin valve by sandwiching the OF between two ferromagnets. By calculating the spin-dependent transport property, we found that the current through the device strongly depends on the alignment of the magnetization orientation of the electrodes and the OF. The spin-related electron tunneling between the ferromagnetic electrodes suffers a further spin selection from the spin-polarized states of the central OF. This work indicates a realization of four-state magnetoresistance based on OFs, which may be manipulated by a magnetic field to control the magnetization orientations of the ferromagnets and the OF. [1] G. C. Hu, M. Y. Zuo, Y. Li, J. F. Ren, and S. J. Xie, Appl. Phys. Lett. 104, 033302 (2014). [2] G. C. Hu, H. Wang, J. F. Ren, S. J. Xie, and C. Timm, Org. Electron. 15, 118 (2014). [3] G. C. Hu, K. L. He, A. Saxena, and S. J. Xie, J. Chem. Phys. 129, 234708 (2008). [4] G. C. Hu, Y. Guo, J. H. Wei, and S. J. Xie, Phys. Rev. B 75, 165321 (2007). [Preview Abstract] |
|
G1.00071: Theoretical study on electronic structure of bathocuproine: Renormalization of the band gap in the crystalline state and the large exciton binding energy Susumu Yanagisawa, Shin-no-Suke Hatada, Yoshitada Morikawa Bathocuproine (BCP) is a promising organic material of a hole blocking layer in organic light-emitting diodes or an electron buffer layer in organic photovoltaic cells. The nature of the unoccupied electronic states is a key characteristic of the material, which play vital roles in the electron transport. To elucidate the electronic properties of the molecular or crystalline BCP, we use the GW approximation for calculation of the fundamental gap, and the long-range corrected density functional theory for the molecular optical absorption. It is found that the band gap of the BCP single crystal is 4.39 eV, and it is in agreement with the recent low-energy inverse photoemission spectroscopy measurement. The polarization energy is estimated to be larger than 1 eV, demonstrating the large polarization effects induced by the electronic clouds surrounding the injected charge. The theoretical optical absorption energy is 3.68 eV, and the exciton binding energy is estimated to be 0.71 eV, implying the large binding in the eletron-hole pair distributed around the small part of the molecular region. [Preview Abstract] |
|
G1.00072: Magneto-conductance of hybrid quantum ring Nammee Kim, Heesang Kim, Dae-Han Park Magneto-conductance behaviors of hybrid magnetic-electric quantum rings are studied. The hybrid magnetic-electric quantum rings are formed by spatially in-homogeneous distributions of magnetic fields and the additional antidot electrostatic potential. Electrons are both magnetically and electrostatically confined to the plane. Electronic structures of hybrid magnetic-electric quantum rings and two terminal conductance taking into account the resonant backscattering via the magnetic edge channels are shown including comparison with the case of a conventional electric quantum ring with uniform external magnetic field. [Preview Abstract] |
|
G1.00073: Local current-voltage characteristic of thin film ferroelectric SrTiO$_3$ Andrew Johnson, Ryan Cottier, Nikoleta Theodoropolou, Joshua Veazey Certain thin-film ferroelectric oxide-semiconductor heterostructures allow for reversible, local changes in conductivity, with potential applications including non-volatile memory devices. Force microscopy techniques were used to investigate the impact of the ferroelectric polarization state on local conductive properties of ferroelectric SrTiO$_3$ (STO) thin films deposited by molecular beam epitaxy onto both p- and n-type Si(001) substrates. Under certain conditions, local current voltage (I-V) curves exhibited pronounced hysteresis under forward bias. These characteristics are not, however, well-correlated with the polarization state of the ferroelectric STO. Alternative explanations for the current hysteresis are presented. This work was generously supported by the Hope College Department of Physics Frissel Research Fund, and the National Science Foundation under NSF-MRI Grant No. CHE-1126462. Support by the NSF-Career grant, DMR-1255629 is gratefully acknowledged. Portions of this work were conducted in the CMP group facilities at Michigan State University; we would like to gratefully acknowledge R. Loloee and the MSU physics department for their support. [Preview Abstract] |
|
G1.00074: Resonant Transmission through Serially Connected Hexagonal Nanorings with Magnetic Flux Effects Eric Hedin, Yong Joe Nanostructures composed of six quantum dots (QDs) connected in a ring are linked together in a linear chain with each ring separated by a coupling segment from adjoining rings. A tight-binding model is used to obtain the electron transmission through an arbitrary number of rings in series as a function of energy, external magnetic field, coupling parameters, and QD site energy values. Modifications of the transmission band structure as a function of external field, due to the Aharonov-Bohm and Zeeman effects, demonstrate control over the conductance properties of the linear chain of nano-rings. Resonant transmission effects (with electron energy equal to the QD site energy values) show a complex dependence upon an interplay of magnetic flux, inter-ring coupling, and the strength of the coupling between the ring system and the external leads. For specific values of lead and ring couplings, nearly full transmission (ballistic transport) is seen to occur across a broad energy range, independent of the number of rings in series. [Preview Abstract] |
|
G1.00075: Achieving Thermodynamic Limit of Subthreshold Slope in Nanoscale Schottky Barrier MOSFET with Pillar Structure Inserted Jung-Yong Lee, Sungchul Jung, Kibog Park As the device size decreases continuously by scaling in the current Si CMOS technology, subthreshold slope which is related to device operation and leakage current becomes more and more important. Especially, the drain induced barrier lowering (DIBL) modulation for improving subthreshold slope in metal/oxide/metal field effect transistor (MOSFET) is difficult to achieve. We propose a new device structure, edge-over Schottky Barrier MOSFET (EO-SB-MOSFET), which shows low DIBL and subthreshold slope approaching the thermodynamic limit of 60 mV/DEC at room temperature. EO-SB-MOSFET has a pillar structure which elongates the transistor channel by forming it over the edge of pillar. Hence, EO-SB-MOSFET has a much longer channel compared with planar MOSFET in the same pitch. We performed 2-dimensional TCAD modeling on an EO-SB-MOSFET with channel lateral size of 6.5 nm and pillar height of 36 nm. The TCAD modeling predicts DIBL of $\sim $5 mV/V, subthreshold slope of $\sim $61.3 mV/DEC, and off-state current of $\sim $0.1 nA/$\mu $m at drain bias 0.5 V. It is also noticed that the subthreshold slope gets further close to the thermodynamic limit as the pillar height increases. [Preview Abstract] |
|
G1.00076: Study of quantum transport in a magnetic wire sankalpa ghosh, Puja Mondol, Ankip Kumar, Alain Nogaret, Harvey Beere, David Ritchie Spatially varying magnetic fields lead to some very interesting physics for two dimensional electron gas. In this work we present some recent results based on the experimental observation of edge states confined by magnetic potentials and their dependence on the strength of the magnetic field strength as well as electrostatic gate voltage By numercially integrating Schroedinger Equation we explain the behavior of such magneto-electric edge states in such two dimensional electron gas. [Preview Abstract] |
|
G1.00077: UNDERGRADUATE RESEARCH |
|
G1.00078: \textbf{Flexo-Electro-Optical Properties of Fullerene-C(Buckyballs) Suspended in 4'-Pentyl-4-Biphenyl (5CB)} Jonathan Foust, Angelo Visco, Rizwan Mahmood We have investigated electro optical properties of a widely studied liquid crystal (5CB) when fullerene C-60 (buckyballs) is suspended in various concentrations as a function of temperature. Under a polarizing microscope, we have observed disclination (defect) points at the sites of buckyballs suggesting a strong interaction between the two components. The data indicate a shift in the transition temperature and sudden decrease in dielectric anisotropy ($\Delta \varepsilon )$ at some critical concentration (\textasciitilde 0.15 wt. {\%}) of fullerene. A sudden increase was also observed upon increasing the concentration of buckyballs that remains constant with in the experimental uncertainty. \textbf{Keywords}: buckyballs, fullerene, liquid crystal, dielectric anisotropy \textbf{Acknowledgements:} RM acknowledges the financial support of the Grant Office, Slippery Rock University. [Preview Abstract] |
|
G1.00079: ABSTRACT WITHDRAWN |
|
G1.00080: Electrical response of monolayer MoS2 to vapors of aliphatic alcohols Pablo Sepulveda, Idalia Ramos, Carl Naylor, A.T. Charlie Johnson, Nicholas Pinto Monolayer MoS2 crystals were used to sense vapors of Methanol, Ethanol and 1-Propanol. Due to the large surface area, these sensors are expected to show rapid response and recovery times. The current through the sensor was monitored as a function of time with a constant applied voltage. This current decreased in the presence of the sensing gas and recovered upon its removal. Our results show that the response time gets longer as the size of the alcohol increases, but the recovery time stays approximately the same (\textasciitilde 20s) regardless of the size of the alcohol. The sensitivity was also seen to decrease as the size of the alcohol increased. These observations could be associated with the slower diffusion of the larger alcohol molecules into the MoS2 crystal. The sensors are also fairly robust since the same sensor was used in all of the measurements after annealing in air at 70C for 10 minutes. Additional sensing measurements as a function of gas concentration will also be presented. [Preview Abstract] |
|
G1.00081: Schottky diode based on WS2 crossed with PEDOT/PSSA Deliris Ortiz, Nicholas Pinto, Carl Naylor, A.T. Charlie Johnson An easy technique to fabricate a Schottky diode with WS2 and PEDOT-PSSA under ambient conditions is presented. WS2 is an air stable transition metal dichalcogenide semiconductor. When connected as a field effect transistor, WS2 exhibited n-type behavior with a charge mobility of \textasciitilde 7cm2/V-s on SiO2. PEDOT/PSSA is a conducting polymer that can be electro-spun to form fibers with a conductivity of \textasciitilde 1 S/cm. In this work we fabricated a Schottky diode by crossing a CVD grown monolayer WS2 crystal with a single electro-spun PEDOT/PSSA fiber. The resulting diode characteristics were analyzed assuming the standard thermionic emission model of a Schottky junction. Analysis of the results includes the ideality parameter of 4.75, diode rectification ratio \textasciitilde 10, and a turn on voltage of 1.4V. Efforts to investigate if these parameters are tunable with a back gate will also be presented. [Preview Abstract] |
|
G1.00082: Opto-electronic Properties of Monolayer-Protected Clusters of Au functionalized with a New Fluorescent Ligand Thomas Kountz, Viraj Thanthirige, Keith Reber, Mary Sajini Devadas Metal nanoclusters are the focus of intense study due to their interesting optical, electronic, and catalytic properties; specifically gold clusters. The applications of gold monolayer-protected clusters (MPCs) are being researched by a series of optical spectroscopic and voltammetric analyses to determine core size, atom-level composition, charge states, and optical/electrical properties. Understanding these fundamental properties is critical for both expansion of applications and creation of new MPCs. The purpose of this study is to expand the applications of gold MPCs, with the attachment of a new coumarin surface ligand - synthesized specifically for this experiment. Our focus in this research is on quantum clusters -- specifically Au$_{25}$(C$_{6}$S)$_{18}$. This MPC is researched particularly because of its inherent stability being a magic number cluster. It is created by means of a modified Burst-Schiffrin method. The applications that are influenced include but are not limited to: catalytic activity, solar energy conversion, size-tunable florescence, sensors, and optical electronics. [Preview Abstract] |
|
G1.00083: Crystallization Trends of PEO-b-PCL with Solvent and Temperature Effects Kristi Allen, Allison Carandang, Ryan Van Horn There is a great deal of interest in being able to selectively modify properties of certain polymers. This increases the amount of control that can be exercised over end products in terms of the hydrophobicity or hydrophilicity, transparency, and brittleness and is highly valued in the biomedical industry. In this case, the crystallization trends of the diblock co-polymer poly(ethylene-oxide)-b-poly($\varepsilon $-caprolactone) (PEO-b-PCL) were observed with the manipulation of solvent and drying temperatures in a variety of samples. The solvents utilized included tetrahydrofuran, chloroform, and toluene. The crystallized samples were scanned via infrared spectroscopy. Results showed highest amounts of PEO crystallization compared to PCL crystallization in toluene while the lowest values were seen in samples in tetrahydrofuran. The chloroform samples fell in the middle. Moderate differences were observed in different molecular weight samples. [Preview Abstract] |
|
G1.00084: Collective dynamics of non-transitively coupled active oscillators Arghyadip Mukherjee, Pawan Nandakishore, Shashi Thutupalli Non-transitive relations between coupled nonequilibrium units are a central feature of many natural and engineered systems ranging from interacting organismal populations to cells in a tissue. As a generalised abstraction for such interactions, we consider a system comprised of units whose internal degrees of freedom are intertwined to their orientation. Specifically, the individual elements are amplitude-phase oscillators with an orientation which can interact with the oscillation phase. An emergent mean field couples their dynamics causing the mesoscopic orientational order of the oscillators to affect their phase dynamics and vice versa. Here, we report on theoretical and experimental results on the emergent dynamics in a system built from mechanical oscillators. We show that the phase space consists of a rich variety of behaviors ranging from orientationally ordered synchronized states, traveling waves and even states with partial ordering. We briefly discuss the biological context for our abstract physical models. [Preview Abstract] |
|
G1.00085: Silicon Photomultipliers Characterization Christopher Bowser, Marian Tzolov, Nick Barbi Low noise and high sensitivity photon detectors such as the Photomultiplier Tube (PMT) are very common instruments used in research and many other applications. The PMTs have drawbacks such as durability, size, and sensitivity to magnetic field which make them unsuitable for some tasks. Silicon Photomultipliers (SiPMs) are compact, solid state detectors with gain close to that of a PMT, which are a promising replacement of a PMT. We have studied two types of SiPMs designed for optimum response in the visible and near-UV spectral range. We have verified the basic electrical parameters of the devices using current-voltage characteristics and impedance spectroscopy in dark. The spectral response was measured in DC mode, which is very simple to realize and still delivers very good sensitivity. We have established the linearity of the photoresponse and the limits at high intensity illumination. The pairing of the SiPMs with several common scintillators was studied with the goal of optimum performance of the SiPM/scintillator pair. [Preview Abstract] |
|
G1.00086: Fabrication of a three dimensional particle focusing microfluidic device using a 3D printer, PDMS, and glass Robyn Collette, Daniel Rosen, Kathryn Shirk Microfluidic devices have high importance in fields such as bioanalysis because they can manipulate volumes of fluid in the range of microliters to picoliters. Small samples can be quickly and easily tested using complex microfluidic devices. Typically, these devices are created through lithography techniques, which can be costly and time consuming. It has been shown that inexpensive microfluidic devices can be produced quickly using a 3D printer and PDMS. However, a size limitation prohibits the fabrication of precisely controlled microchannels. By using shrinking materials in combination with 3D printing of flow-focusing geometries, this limitation can be overcome. This research seeks to employ these techniques to quickly fabricate an inexpensive, working device with three dimensional particle focusing capabilities. By modifying the channel geometry, colloidal particles in a solution will be focused into a single beam when passed through this device. The ability to focus particles is necessary for a variety of biological applications which requires precise detection and characterization of particles in a sample. [Preview Abstract] |
|
G1.00087: Statistical Modeling of Robotic Random Walks on Different Terrain Austin Naylor, Laura Kinnaman Issues of public safety, especially with crowd dynamics and pedestrian movement, have been modeled by physicists using methods from statistical mechanics over the last few years. Complex decision making of humans moving on different terrains can be modeled using random walks (RW) and correlated random walks (CRW). The effect of different terrains, such as a constant increasing slope, on RW and CRW was explored. LEGO robots were programmed to make RW and CRW with uniform step sizes. Level ground tests demonstrated that the robots had the expected step size distribution and correlation angles (for CRW). The mean square displacement was calculated for each RW and CRW on different terrains and matched expected trends. The step size distribution was determined to change based on the terrain; theoretical predictions for the step size distribution were made for various simple terrains. [Preview Abstract] |
|
G1.00088: Novel Fabrication of Carbon Spheres Decorated with Nickel Nanoparticles for Supercapacitors Cesar Nieves, Joshua Robles, Nicholas Pinto, Idalia Ramos Carbon spheres (CS) were synthesized by hydrothermal method using a 0.8M aqueous sucrose solution as the carbon source. The starting solution was heated in a stainless steel autoclave at 200$^{\circ }$C for 4h to produce carbon spheres with regular shapes having diameters in the range of 1-20$\mu $m. Ni-nanoparticles were deposited on the CS surfaces by an electro-less deposition technique. Our work is the first attempt to decorate CS with nickel nanoparticles using this method. The obtained Ni-CS was studied using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Ultra-Violet/Visible Spectroscopy (UV-Vis). CS decorated with Nickel nanoparticles increase their capacity to conduct a current making them useful in catalysts and in supercapacitors. Conductivity measurements on these Ni decorated CS and their use in supercapacitors will be presented. [Preview Abstract] |
|
G1.00089: Utilizing Diffuse Reflection to Increase the Efficiency of Luminescent Solar Concentrators Seth Bowser, Seth Weible, Joel Solomon, Jonathan Schrecengost, Bruce Wittmershaus A luminescent solar concentrator (LSC) consists of a high index solid plate containing a fluorescent material that converts sunlight into fluorescence. Utilizing total internal reflection, the LSC collects and concentrates the fluorescence at the plate’s edges where it is converted into electricity via photovoltaic solar cells. The lower production costs of LSCs make them an attractive alternative to photovoltaic solar cells. To optimize an LSC’s efficiency, a white diffusive surface (background) is positioned behind it. The background allows sunlight transmitted in the first pass to be reflected back through the LSC providing a second chance for absorption. Our research examines how the LSC’s performance is affected by changing the distance between the white background and the LSC. An automated linear motion apparatus was engineered to precisely measure this distance and the LSC’s electrical current, simultaneously. LSC plates, with and without the presence of fluorescent material and in an isolated environment, showed a maximum current at a distance greater than zero. Further experimentation has proved that the optimal distance results from the background’s optical properties and how the reflected light enters the LSC. [Preview Abstract] |
|
G1.00090: Improving the Stability of Fluorescent Silver Nanoclusters Nicholas Swanson, Danielle Stanko, Ian Campbell, Bruce Wittmershaus The quantum mechanical nature of noble metal nanoparticles results in them having optical properties much different from the bulk metal. Silver nanoclusters (AgNC), groups of 4 to 20 atoms, are characterized by strong optical transitions in the visible part of the spectrum giving them an appearance like fluorescent organic dyes. These nanoclusters can also have fluorescence quantum yields over 90\%. Following the analysis of published results of DNA templated nanoclusters, we created a procedure for synthesizing AgNC. The AgNC have a high fluorescence quantum yield but degrade with a lifetime of only a few days when in solution at room temperature. Our goal in this study was to increase the stability of the AgNC towards improving their value as a fluorescent material in various applications, such as luminescent solar concentrators. To increase their stability, we’ve chosen to modify our procedure by removing oxygen from the solution after the sample has reacted. Oxygen removal caused a significant increase in the stability of the clusters over a given period of time. [Preview Abstract] |
|
G1.00091: Equivalence Principle tests as probes of Modified Newtonian Dynamics Alex Poyneer, Jonas Pereira, Thomas Krause, James Overduin Modified Newtonian dynamics (MOND) has been proposed as a way to reconcile gravitational theory and observational cosmology without the need for large amounts of unseen dark matter. Instead, a change is postulated to the Newtonian limit of standard theory in the regime of very small accelerations. We consider whether it might be possible to constrain this idea using proposed space tests of the Equivalence Principle (EP). Such tests could be sensitive to accelerations as small as 10$^{\mathrm{-18\thinspace }}$g over 20 orbits. [Preview Abstract] |
|
G1.00092: Concentration Dependence of Gold Nanoparticles for Fluorescence Enhancement Joel Solomon, Bruce Wittmershaus Noble metal nanoparticles possess a unique property known as surface plasmon resonance in which the conduction electrons oscillate due to incoming light, dramatically increasing their absorption and scattering of light. The oscillating electrons create a varying electric field that can affect nearby molecules. The fluorescence and photostability of fluorophores can be enhanced significantly when they are near plasmonic nanoparticles. This effect is called metal enhanced fluorescence (MEF). MEF from two fluorescence organic dyes, Lucifer Yellow CH and Riboflavin, was measured with different concentrations of 50-nm colloidal gold nanoparticles (Au-NP). The concentration range of Au-NP was varied from 2.5 to 250 pM. To maximize the interaction, the dyes were chosen so their emission spectra had considerable overlap with the absorption spectra of the Au-NP, which is common in MEF studies. If the dye molecules are too close to the surface of Au-NP, fluorescence quenching can occur instead of MEF. To try to observe this difference, silica-coated Au-NP were compared to citrate-based Au-NP; however, fluorescence quenching was observed with both Au-NP. [Preview Abstract] |
|
G1.00093: Local density of states measurements via STM and TS on clean fresh cleaved HOPG and Gold thin films on HOPG under ambient conditions. Casey Morean, Roman Marijczuk, Indrajith Senevirathne Highly Oriented Pyrolytic Graphite (HOPG) has many applications in physics and engineering thus understanding affiliated physical and chemical phenomena is important. This also makes HOPG an important and interesting system to study. This is an investigation of surfaces of HOPG and Au thin films (ranging about 20nm) via Scanning Tunneling Microscopy (STM) and Tunneling Spectroscopy (TS) with a Pt-Ir tip equipped Nanosurf Naio STM. In this investigation, clean fresh cleaved HOPG substrates were used. Surfaces of HOPG and Au sputter deposited at different film thicknesses were imaged via constant current mode to assess the surface consistency and roughness. Consistent atomic resolution images were obtained. The systems were then investigated via TS by applied tip voltage (V) vs. tunneling current (I) curves. These spectroscopic data were then used to assess the local density of states (LDOS) and the surface variation of LDOS. The discussion will attempt to assess the surface electronic environment of these systems in relation to the Au deposition and variation of Au thicknesses on HOPG. Since measurements were carried out in ambient conditions this adds to the complexity which will also be discussed. [Preview Abstract] |
|
G1.00094: Gravity Wave Disturbances in the F-Region Ionosphere Above Large Earthquakes Margie Bruff The direction of propagation, duration and wavelength of gravity waves in the ionosphere above large earthquakes were studied using data from the Super Dual Auroral Radar Network. Ground scatter data were plotted versus range and time to identify gravity waves as alternating focused and de-focused regions of radar power in wave-like patterns. The wave patterns before and after earthquakes were analyzed to determine the directions of propagation and wavelengths. Conditions were considered 48 hours before and after each identified disturbances to exclude waves from geomagnetic activity. Gravity waves were found travelling away from the epicenter before all six earthquakes for which data were available and after four of the six earthquakes. Gravity waves travelled in at least two directions away from the epicenter in all cases, and even stronger patterns were found for two earthquakes. Waves appeared, on average, 4 days before, persisting 2-3 hours, and 1-2 days after earthquakes, persisting 4-6 hours. Most wavelengths were between 200-300 km. We show a possible correlation between magnitude and depth of earthquakes and gravity wave patterns, but study of more earthquakes is required. This study provides a better understanding of the causes of ionospheric gravity wave disturbances and has potential applications for predicting earthquakes. [Preview Abstract] |
|
G1.00095: Work function measurements via STM and TS on clean fresh cleaved HOPG and Gold thin films on HOPG under ambient conditions. Roman Marijczuk, Casey Morean, Indrajith Senevirathne Stability and homogeneity of HOPG has enabled it to be used as a platform for various applications in understanding many physical and chemical phenomena. Novel emergence of graphene as a derivative of graphite also makes HOPG an interesting system to study. This is an ambient investigation of HOPG and Au thin films (ranging about 20nm) surfaces via Scanning Tunneling Microscopy (STM) and Tunneling Spectroscopy (TS) with a Pt-Ir tip equipped Nanosurf Naio STM. In this investigation, clean fresh cleaved HOPG substrates were used. Surfaces of HOPG and Au sputter deposited at different film thicknesses were imaged via constant current mode to assess the surface consistency and roughness. Consistent atomic resolution images were obtained. The same systems were then investigated via TS by tunneling current (I) vs. height (z) curves. These spectroscopic data were then used to assess the localized work function measurements and surface variation of the work function. The discussion will attempt to assess the surface electronic environment of these systems in relation to the Au deposition and variation of Au thickness on HOPG. Ambient measurements will inherently complicate these measurements and the complexities will also be discussed. [Preview Abstract] |
|
G1.00096: Basic atmospheric measurements via Arduino Uno microcontroller with commercially available sensors towards simple real-time weather forecasting for increased classroom engagement Ryan Eckel, Meghan Tanner, Indrajith Senevirathne Makers, engineers and the applied physics community have adapted Arduino microcontrollers due to their versatility, robustness and cost effectiveness. Arduino microcontroller environment coupled with commercially available sensors have been used to systematically measure, record and analyze temperature, humidity and barometric pressure for building a simplified weather station for subsequent educational purposes. This data will become available in classroom settings for real-time analysis towards simple weather forecasting. Setup was assembled via breadboard, wire and simple soldering with an Arduino Uno ATmega328P microcontroller connected to a PC. The microcontroller was programmed with Arduino Software while the bootloader was used to upload the code. Commercial DHT22 humidity and temperature sensor, and BMP180 barometric pressure sensor were used to obtain relative humidity, temperature and the barometric pressure. A weather resistant enclosure protected the system while stable real-time data measurements were obtained, and uploaded onto the PC. The data was used to predict atmospheric conditions and lifting condensation level (LCL). Discussion will focus on capabilities and limitations of these systems and corresponding teaching aspects. [Preview Abstract] |
|
G1.00097: Enhanced low current, voltage, and power dissipation measurements via Arduino Uno microcontroller with modified commercially available sensors. Meghan Tanner, Ryan Eckel, Indrajith Senevirathne The versatility, simplicity, and robustness of Arduino microcontroller architecture have won a huge following with increasingly serious engineering and physical science applications. Arduino microcontroller environment coupled with commercially available sensors have been used to systematically measure, record, and analyze low currents, low voltages and corresponding dissipated power for assessing secondary physical properties in a diverse array of engineering systems. Setup was assembled via breadboard, wire, and simple soldering with an Arduino Uno with ATmega328P microcontroller connected to a PC. The microcontroller was programmed with Arduino Software while the bootloader was used to upload the code. Commercial Hall effect current sensor modules ACS712 and INA169 current shunt monitor was used to measure corresponding low to ultra-low currents and voltages. Stable measurement data was obtained via sensors and compared with corresponding oscilloscope measurements to assess reliability and uncertainty. Sensor breakout boards were modified to enhance the sensitivity of the measurements and to expand the applicability. Discussion of these measurements will focus on capabilities, capacities and limitations of the systems with examples of possible applications. [Preview Abstract] |
|
G1.00098: Photocurrent of Photovoltaic Cells Seth Peeler, Max McIntyre, Raquel Cossel, Chris Bowser, Marian Tzolov Photovoltaic cells can be used to harness clean, renewable energy from light. Examined in this project were photovoltaic cells based on a bulk heterojunction between PCPDTBT and PCBM sandwiched between an ITO anode and an Al cathode. Current-voltage characteristics and impedance spectra for multiple photovoltaic devices were taken under varying DC electrical bias and different level of illumination. This data was interpreted in terms of an equivalent circuit with linear elements, e.g. capacitance, series resistance, and parallel resistance. A physical interpretation of each circuit element will be presented. The spectral response of the devices was characterized by optical transmission and photocurrent spectroscopy using a spectrometer in the spectral range from 300 to 900 nm. The DC measurements confirmed that the devices are electrically rectifying. The AC measurements allowed modeling of the devices as a dielectric between two electrodes with injection current passing through it. The characteristic peaks for both PCBDTBT and PCBM are clearly visible in both the photocurrent and transmission data. The good correlation between the photocurrent and transmission data indicates photocurrent generation due to absorption in both materials constituting the heterojunction. [Preview Abstract] |
|
G1.00099: Characterization of the Pseudocapacitive Nature of Surface Bound Prussian Blue Analogues Daniel Clark, Jennifer Hampton With the increased use of intermittent renewable energy sources, more efficient methods of energy storage must be explored. Electrochemical capacitors provide a larger volumetric charge density than physical capacitors while maintaining fast charge and discharge rates. Prussian Blue analogues (nickel and cobalt hexacyanoferrate) are ideal pseudocapacitors for frequent charge and discharge cycles since the crystalline structure does not physically change during switching, causing less stress on the film. This project examines the charge transfer and diffusion coefficients for nickel and nickel-cobalt thin films modified with potassium hexacyanoferrate. The films were examined using a scanning electron microscope, an atomic force microscope and an electrochemical workstation to determine their composition, topography and psuedocapacitive nature. Preliminary data suggest that nickel-cobalt films have a larger quantity of charge and have a lower diffusion coefficient per charge than nickel films. [Preview Abstract] |
|
G1.00100: Dealloying NiCo and NiCoCu Alloy Thin Films Using Linear Sweep Voltammetry Benjamin Peecher, Jennifer Hampton When electrodeposited into thin films, metals have well-known electrochemical potentials at which they will be removed from the film. These potential differences can be utilized to re-oxidize only certain metals in an alloy, altering the film’s structure and composition. Here we discuss NiCo and NiCoCu thin films’ response to linear sweep voltammetry (LSV) as a means of electrochemical dealloying. For each of four different metal ratios, films were dealloyed to various potentials in order to gain insight into the evolution of the film over the course of the LSV. Capacitance, topography, and composition were examined for each sample before and after linear sweep voltammetry was performed. For NiCo films with high percentages of Ni, dealloying resulted in almost no change in composition, but did result in an increased capacitance, with greater increases occurring at higher LSV potentials. Dealloying also resulted in the appearance of large (100--1000 nm) pores on the surface of the film. For NiCoCu films with high percentages of Ni, Cu was almost completely removed from the film at LSV potentials greater than 500 mV. The LSV first removed larger copper-rich dendrites from the film’s surface before creating numerous nano-pores, resulting in a net increase in area. [Preview Abstract] |
|
G1.00101: Effects of Stress on Corrosion in a Molten Salt Environment Samuel Girdzis, Dennis Manos, William Cooke Molten salt is often used as a heat transfer and energy storage fluid in concentrating solar power plants. Despite its suitable thermal properties, molten salt can present challenges in terms of corrosion. Previous studies have focused extensively on mass loss due to molten salt-induced corrosion. In contrast, we have investigated how corrosion begins and how it changes the surface of stainless steel. Samples of alloys including 304 and 316 stainless steel were exposed to the industry-standard NaNO$_3$-KNO$_3$ (60\%-40\% by weight) mixture at temperatures over 500$^{\circ}$C and then analyzed using Hirox, SEM, and TOF-SIMS. We compare the corrosion at grain boundaries to that within single grain surfaces, showing the effect of the increased internal stresses and the weakened passivation layer. Also, we have examined the enhanced corrosion of samples under mechanical stress, simulating the effects of thermal stresses in a power plant. [Preview Abstract] |
|
G1.00102: Exact and Approximate Solutions for a Class of Cooperative Stochastic Models Rebecca Melkerson, Gillenhaal Beck, Estevan Hall-Mejia, Sabin Nshimyumukiza, Carlos da Fonseca, Dan Mazilu, Irina Mazilu We present a class of cooperative sequential adsorption models with evaporation defined on general lattice structures. Using matrix algebra theory to solve the associated master equations, we find the time-dependent probability distributions. We discuss these models in the context of ionic self-assembly of silica nanoparticles in order to also find the time-dependent surface coverage. To test the limits of the matrix theory, we add the possibilities for evaporation either once the surface is fully covered or at intermediate steps. We justify our mathematical models by comparing the results to customized experiments and computer simulations. [Preview Abstract] |
|
G1.00103: Potential Mapping of an Indium-Tin-Oxide Glass Box in a GEC Reference Cell Rebecca Kaplan, Jorge Carmona-Reyes, Truell Hyde, Lorin Matthews The use of indium-tin-oxide (ITO) coated boxes, as well as boxes coated with other substances, placed on or floating above the lower electrode in studies using Gaseous Electronics Conference Radio Frequency Reference Cells have increased in interest, as have the use of plain glass boxes. This increase in interest is due to the greater ability to control the confinement forces and in effect create dust chain structures which aid in studies within other areas of physics such as; entropy, kinetic dust temperature, plasma balls and coulomb explosions. Further analysis of the data obtained using these boxes shows what appear to be at least two different regions of confinement inside the boxes as well as some unexpected phenomena related to anomalous values and behavior of the electric field. These areas affect the dust to dust and dust to plasma interactions independently in the separate regions and are therefore of great interest. In this study electric potential and electric field maps created in MatLab with data obtained using two probes mounted on CASPER's S-100 nano-manipulator will be presented, connecting the information obtained from these maps to the behavior of the dust observed for different experimental conditions. [Preview Abstract] |
|
G1.00104: Deducing Shape of Anisotropic Particles in Solution from Light Scattering: Spindles and Nanorods. Ilona Tsuper, Daniel Terrano, Kiril A. Streletzky, Olga V. Dement'eva, Sergey A. Semyonov, Victor M. Rudoy Depolarized Dynamic Light Scattering (DDLS) enables to measure rotational and translational diffusion of nanoparticles suspended in solution. The particle size, shape, diffusion, and interactions can then be inferred from the DDLS data using various models of diffusion. Incorporating the technique of DDLS to analyze the dimensions of easily imaged elongated particles, such as Iron (III) oxyhydroxide (FeOOH) Spindles and gold Nanorods, allows testing of the models for rotational and translational diffusion of elongated particles in solution. This, in turn, can help to better interpret DDLS data on hard-to-image anisotropic wet systems such as micelles, microgels, and protein complexes. This study focused on FeOOH Spindles and gold nanorod particles. The light scattering results on FeOOH analyzed using the basic model of non-interacting prolate ellipsoids yielded dimensions within 17{\%} of the SEM measured dimensions. The dimensions of gold nanorod obtained from the straight cylinder model of DDLS data provided results within 25{\%} of the sizes that were obtained from TEM. The nanorod DDLS data was also analyzed by a spherocylinder model. [Preview Abstract] |
|
G1.00105: Developing Affordable Wet-Sample Electron Microscopy Integrated with a Temperature Controlled Sample Holder. Daniel Terrano, Petru S. Fodor, Kiril A. Streletzky Scanning electron microscopy (SEM) is widely used to analyze the size, shape and composition of material systems. However, using this tool for analyzing systems such as particles suspended in solution, requires drastic sample alterations, such as precipitation and fixation. Besides altering their environment, this exposes the particles to the harsh conditions within an electron microscope, such as high vacuum and electron beam exposure. To this end, the first goal of this study was to develop methodologies for imaging wet samples using electron microscopy. This is realized by creating a sandwich structure containing the solution of interest between a partially electron transparent window and a silicon substrate. The ability of the developed imaging cells to provide good imaging conditions is demonstrated with a variety of samples including polystyrene spheres, polymeric microgels and spindle shaped nanoparticles. As some of the systems investigated are temperature sensitive, the second goal of the project was to develop a temperature controlled stage that can be integrated with the SEM. In the future this heating stage will be used alongside the wet samples to image microgels above and below their critical solution temperature. [Preview Abstract] |
|
G1.00106: Deposition of Highly Luminescent Zinc Tungstate Thin Films on Various Substrates Rashad Farrakhan Zinc tungstate films have promising applications in small form factor backscatter electron detectors. We are developing a multistep technology for synthesis of these films. Zinc and tungsten were co-sputtered onto substrates through the process of magnetron sputtering. The metallic films were oxidized in a vacuum sealed tube furnace in controlled flow of argon and oxygen at 800 \textdegree C. The chemical composition of the film was characterized by Energy-Dispersive X-Ray Spectroscopy (EDS). The structure of the film was investigated by Raman Spectroscopy. The photoluminescence quantum efficiency of the films was found to be 60{\%}. Process parameters for obtaining the desired 1-1 ratio of zinc to tungsten in the film is explored through varying factors such as: the composition of the target used in the sputtering, the power and or voltage used in the sputtering process. Our experiments show that zinc tungstate thin films can be deposited on various substrates with good adhesion and mechanical integrity, and still be efficient light emitters. [Preview Abstract] |
|
G1.00107: ABSTRACT WITHDRAWN |
|
G1.00108: Synthesis of Polymeric Microgels and their Characterization with Light Scattering. Christian Gunder, Kiril A. Streletzky, Krista Freeman, Janna Mino Polymeric microgels were synthesized in by chemically crosslinking hydroxypropylcellulose (HPC) chains in aqueous solutions of sodium hydroxide at temperatures above the low critical solution temperature (LCST) of HPC. In order to create a narrower size distribution of HPC microgels, surfactant was added. It was found that the LCST of the solution moved from 40C up to 80C with an increase in surfactant concentration from 0 to 12 g/l. Formed microgels were characterized by dynamic light scattering (DLS). Microgel solutions synthesized resulted in reasonably monodispersed nanoparticles with Rh of 90-150 nm below the transition, and Rh of 50-90 nm above the transition. The effect of synthesis temperature and crosslinker concentration on microgel size, polydispersity, and swelling ratio were also studied. [Preview Abstract] |
|
G1.00109: Monte Carlo and Exact Diagonalization of Copper (II) Trimer Spin Frustrated Systems Hailey X. Egido-Betancourt, Leonard W. ter Haar, Christopher N. Varney We discuss the use and importance of trimer-based systems because of the spin frustration that may arise within extended lattices comprised of trimers. The possible intra- and inter-trimer exchange pathways they posses due to interconnections are evaluated using density functional theory (DFT) to identify the optimal structures that may be used in designing extended lattices. As example, trinuclear Cu$_3^{6+}$cores with each pair of copper atoms bridged by carboxylate ligands have three-fold symmetry. As trimers these structures have the potential to be modeled as a frustrated quantum spin-1/2 system. To analyze the magnetic ground state and topological properties, we utilize exact diagonalization on small clusters and compare with Monte Carlo simulations for a range of system sizes. [Preview Abstract] |
|
G1.00110: Tensile Strain Effects on the Magneto-transport in Calcium Manganese Oxide Thin Films: Comparison with its Hole-doped Counterpart Bridget Lawson, Samuel Neubauer, Adeel Chaudhry, Cacie Hart, Natalie Ferrone, David Houston, Grace Yong, Rajeswari Kolagani Magnetoresistance properties of the epitaxial thin films of doped rare earth manganites are known to be influenced by the effect of bi-axial strain induced by lattice mismatch with the substrate. In hole-doped manganites, the effect of both compressive and tensile strain is qualitatively consistent with the expected changes in unit cell symmetry from cubic to tetragonal, leading to Jahn-Teller strain fields that affect the energy levels of Mn3$+$ energy levels. Recent work in our laboratory on CaMnO$_{\mathrm{3}}$ thin films has pointed out that tetragonal distortions introduced by tensile lattice mismatch strain may also have the effect of modulating the oxygen content of the films in agreement with theoretical models that propose such coupling between strain and oxygen content. Our research focuses on comparing the magneto-transport properties of hole-doped manganite LaCaMnO$_{\mathrm{3}}$ thin films with that of its electron doped counter parts, in an effort to delineate the effects of oxygen stoichiometry changes on magneto-transport from the effects of Jahn-Teller type strain. [Preview Abstract] |
|
G1.00111: Heat of Combustion of Dried and Undried Coffee Mathew Giso, Samuel Amanuel Globally, over two billion cups of coffee are consumed per day. During roasting, 15-20{\%} of the weight of the coffee beans is lost. We studied the gasses released during the roasting process using an IR spectrometer and identified the evaporation profile of water as a function of temperature. The heat of combustion (H\textordmasculine c) of the beans was also determined using an Isoperibol Oxygen-Bomb calorimeter and the H\textordmasculine c of dry beans were determined to be 21.24 \textpm 0.13 MJ/kg while the H\textordmasculine c of the wet beans were determined to be 19.56 \textpm 0.12 MJ/kg. This study can potentially lead to developing more economical and environmentally friendly techniques of roasting coffee beans. [Preview Abstract] |
|
G1.00112: Visualizing Sound: Demonstrations to Teach Acoustic Concepts Valerie Rennoll Interference,~a phenomenon in which two sound~waves~superpose~to form a resultant wave of greater or lower~amplitude, is a key concept when learning about the physics of sound waves.~ Typical interference demonstrations involve students listening for changes in sound level as they move throughout a room.~ Here, new tools are developed to teach this concept that provide a visual component, allowing individuals to see changes in sound level on a light display.~ This is accomplished using a microcontroller that analyzes sound levels collected by a microphone and displays the sound level in real-time on an LED strip.~ The light display is placed on a sliding rail between two speakers to show the interference occurring between two sound waves.~ When a long-exposure photograph is taken of the light display being slid from one end of the rail to the other, a wave of the interference pattern can be captured.~ By providing a visual component, these tools will help students and the general public to better understand interference, a key concept in acoustics. [Preview Abstract] |
|
G1.00113: Effect of Uniaxial Strain on Band Structure of Multi-layer WS$_{\mathrm{2}}$* Conrad Troha, Duy Le, Talat Rahman The ability to tailor band structure of a multi-layer transition metal dichalcogenide is of interest because it opens up utilizations of the material for various applications. Strain is considered a robust way to alter the electronic structure of a material. We performed calculations, using density functional theory, of band structure of multi-layer WS$_{\mathrm{2}}$ under the effects of uniaxial strain. We show that the position of the bottom of conduction band (BCB) at $\sum $ moves to higher, and at K to lower, energy levels under the effects of uniaxial tensile strain, making multi-layer WS$_{\mathrm{2}}$ closer to a direct band gap material. Our results suggest that uniaxial tensile strain can be used to alter band structure of multi-layer WS$_{\mathrm{2}}$ to achieve higher yield photo luminescence. [Preview Abstract] |
|
G1.00114: Complexity and Fly Swarms Grant Cates, Joelle Murray Complexity is the study of phenomena that emerge from a collection of interacting objects and arises in many systems throughout physics, biology, finance, economics and more. Certain kinds of complex systems can be described by self-organized criticality (SOC). An SOC system is one that is internally driven towards some critical state. Recent experimental work suggests scaling behavior of fly swarms--one of the hallmarks of an SOC system. Our goal is to look for SOC behavior in computational models of fly swarms. [Preview Abstract] |
|
G1.00115: Gas separation by adsorption in carbon nanohorns. Anton Nekhai, Silvina Gatica Gas separation by adsorption can be accomplished by three basic physical mechanisms: equilibria, kinetics, and steric effects. Equilibrium mechanisms rely on the strength of attraction between gas molecules and their substrate. For example, CO$_{2}$ possesses the strongest, attractive interactions with its substrate. As a result, the equilibrium mechanism presents the most plausible strategy to separate carbon dioxide from mixtures. The specification of a sound adsorbent is the key for separation by adsorption. In this paper we investigate carbon nanohrons for selectivity of carbon dioxide over methane. Carbon Nanohorns resemble short, wide, highly defected single-wall nanotubes that end in conical tips (``horns''). In contrast to regular nanotubes that assemble into parallel bundles, nanohorns form spherical aggregates with the nanohorns arranged along radial directions. Using the simulation technique Grand Canonical Monte Carlo (GCMC) we obtained the adsorption isotherms of CH$_{4}$ and CO$_{2}$ in a 2D array of carbon nanohorns. We estimated the selectivity based on the IAST approximation. We also study the adsorption of argon and neon and compare with experimental results. [Preview Abstract] |
|
G1.00116: Doped Lanthanum Hafnates as Scintillating Materials for High-Energy Photon Detection Kareem Wahid, Madhab Pokhrel, Yuanbing Mao Recent years have seen the emergence of nanocrystalline complex oxide scintillators for use in X-ray and gamma-ray detection. In this study, we investigate the structural and optical properties of La$_{2}$Hf$_{2}$O$_{7}$ nanoparticles doped with varying levels of Eu$^{3+}$ or Ce$^{3+}$ by use of X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and optical photoluminescence. In addition, scintillation response under X-ray and gamma-ray exposure is reported. [Preview Abstract] |
|
G1.00117: ABSTRACT WITHDRAWN |
|
G1.00118: Controlled, Pulsed Frequency Chirped Laser Light at Large Detuning Tracy Paltoo, Tanner Grogan, Brian Kaufman, Matthew Wright We have developed a technique to create pulsed, frequency chirped laser light (1 GHz in 5 ns) at large detuning (\textgreater 7 GHz). Laser light is passed through an electro-optical phase modulator, where the light is modulated with a 7 GHz carrier signal whose frequency is modulated on the nanosecond time scale. The modulated light is passed into a diode laser which becomes injection locked. The injection-locked laser system amplifies and filters the laser light to create a single frequency chirped laser pulse whose detuning is some multiple of the carrier frequency. We have developed the ability to pulse the laser on timescales less than 3 ns and create an arbitrary frequency chirp shape. [Preview Abstract] |
|
G1.00119: Whispering Gallery Modes Used to Determine the Changing Size of Levitated Aerosol Droplets in a Fluctuating Optical Trap Angela Ludvigsen, Lowell McCann A laser can be used as an optical trap to catch and hold small, transparent objects. Observations of optically trapped aqueous aerosol droplets have demonstrated that the droplet moves between two or more stable positions dependent upon the power of the trapping laser. It is hypothesized that this movement coincides with a resonance between the trapping light and the droplet's surface, called a Whispering Gallery Mode. When this resonance occurs, forces acting on the droplet cause it to move. To investigate this behavior, Raman scattered light from the droplet as well as the droplet's position are measured. The Raman spectrum exhibits a series of peaks resulting from the droplet's spherical shape, referred to as Cavity Enhanced Raman Spectroscopy. The location and spacing of these peaks are known to be related to the diameter and the optical properties of the droplet. From this spectrum, the magnitude of the electric and magnetic fields of the scattered light are calculated. This allows for a precise measurement of the droplet's radius at the moment that the droplet moves between stable positions. After determining the droplet's radius from the spectrum, the effect of varying the intensity of the trapping laser beam on the droplet radius can be investigated. [Preview Abstract] |
|
G1.00120: Apparatus for the Measurement of Thermoelectric Power Shoji Hishida, Pei-Chun Ho The Seebeck Effect refers to the electric potential that is established in a material under an imposed temperature gradient. This effect provides a useful tool for characterizing the thermal and electric transport behavior of materials. A measurement probe is under development in order to measure the Seebeck Coefficient (Thermoelectric Power) of a sample over the temperature range from 10 - 300 K in a cryocooler system. The sample is mounted between two platforms: one that is thermally connected with the measurement probe and another that is thermally isolated, referred to as the cold and hot platforms respectively. A 2k$\Omega$ resistance heater on the hot platform is used to establish a temperature gradient across the sample and between the two platforms. A Cernox resistance thermometer measures the temperature of the cold platform, and a Type T differential thermocouple, composed of copper-constantan-copper wires, is used to measure the temperature difference. The probe will be calibrated using the known thermopowers of Nickel, Platinum, and Chromel samples. The performance results of this design will be presented. [Preview Abstract] |
|
G1.00121: Two Undergraduate Projects for Data Acquisition and Control Kelly Hiersche, Tara Pena, Tanner Grogan, Matthew Wright We are designing two separate instruments for use in our undergraduate laboratory. In the first project, a Raspberry Pi is used to simultaneously monitor a large number of current and voltage readings and store them in a database. In our second project, we are constructing our own microcontrollers to work as a general-purpose interface based off work carried out in Review of Scientific Instruments \textbf{84}, 103101 (2013). It was designed for low cost and simple construction, making it ideal for undergraduate level work. This circuit has room for two interchangeable daughter boards, giving it the capability to work as a general lab interface, lock-in detector, or waveform generator. [Preview Abstract] |
|
G1.00122: Anion Photoelectron Spectroscopy of the Homogenous 2-Hydroxypyridine Dimer Electron Induced Proton Transfer System Alexandra Vlk, Sarah Stokes, Yi Wang, Zachary Hicks, Xinxing Zhang, Nicolas Blando, Andrew Frock, Sara Marquez, Kit Bowen Anion photoelectron spectroscopic (PES) and density functional theory (DFT) studies on the dimer anion of (2-hydroxypyridine)$_{\mathrm{2}}^{\mathrm{-}}$ are reported. The experimentally measured vertical detachment energy (VDE) of 1.21eV compares well with the theoretically predicted values. The 2-hydroxypyridine anionic dimer system was investigated because of its resemblance to the nitrogenous heterocyclic pyrimidine nucleobases. Experimental and theoretical results show electron induced proton transfer (EIPT) in both the lactim and lactam homogeneous dimers. Upon electron attachment, the anion can serve as the intermediate between the two neutral dimers. A possible double proton transfer process can occur from the neutral (2-hydroxypyridine)$_{\mathrm{2}}$ to (2-pyridone)$_{\mathrm{2\thinspace }}$through the dimer anion. This potentially suggests an electron catalyzed double proton transfer mechanism of tautomerization. [Preview Abstract] |
|
G1.00123: Charge Transport and Stuctural Dynamics in Phosphonium-based Ionic Liquids Zachariah Vicars, Tyler Cosby, Yangyang Wang, Katsuhiko Tsunashima, Joshua Sangoro A series of phosphonium-based ionic liquids are investigated by broadband dielectric spectroscopy, rheology, and differential scanning calorimetry. Varying the molecular structure of the anion leads to significant changes in charge transport and structural dynamics. The results are discussed within the framework and current understanding of anion/cation interactions in determining physicochemical properties of ionic liquids. [Preview Abstract] |
|
G1.00124: Protein Folding and Self-Organized Criticality Arun Bajracharya, Joelle Murray Proteins are known to fold into tertiary structures that determine their functionality in living organisms. However, the complex dynamics of protein folding and the way they consistently fold into the same structures is not fully understood. Self-organized criticality (SOC) has provided a framework for understanding complex systems in various systems (earthquakes, forest fires, financial markets, and epidemics) through scale invariance and the associated power law behavior. In this research, we use a simple hydrophobic-polar lattice-bound computational model to investigate self-organized criticality as a possible mechanism for generating complexity in protein folding. [Preview Abstract] |
|
G1.00125: Construction of a Laser Induced Breakdown Spectroscopy Setup Joseph Mays, Andria Palmer, James Amos, Tom Dynka, Lazlo Ujj Laser Induced Breakdown Spectroscopy (LIBS) is a practical spectroscopy to determine the chemical and atomic composition of materials. The third harmonic output of a Nd:YAG Q-switched laser generating 5ns pulses with 10Hz repetition rate was used to ablate the sample and create a micro-plasma. The emission of the radiating plasma was focused into an optical fiber with 0.22 numerical aperture. The spectra was measured with an Ocean Optics micro spectrometer. A synchronized shutter was used to select single laser pulses. In order to reach the breakdown threshold of the sample using the available energy of the laser pulses (\textless 5 mJ) a beam expander and a parabolic mirror was used for tight focusing. The optical and technical details including the characterization of the system will be presented. LIBS spectra taken from a variety of metal and organic samples show appropriate selectivity for quantitative and qualitative analysis for materials. [Preview Abstract] |
|
G1.00126: Assessing the Effectiveness of Gravitational Wave Outreach Video Games in High School Students Jonathan Wheeler Students and faculty at the Gravitational Wave Group in Birmingham, UK developed a remake of the classic 1972 game of Pong. Black Hole Pong was developed to be used in events such as science fairs as a way to engage children and pique interest in black holes. I present the results of a study which assesses the utility of Black Hole Pong and its successors in raising awareness of gravitational wave research, and in fostering conceptual understanding of astrophysics and gravity. Of particular interest in this study is potential use in high school science classrooms during astrophysics units. [Preview Abstract] |
|
G1.00127: All-Optical Quasi-Phase Matching of Frequency Doubling Using Counterpropagating Light Richard Camuccio, Rachel Myer, Allison Penfield, Etienne Gagnon, Amy Lytle Nonlinear optical frequency conversion is a useful method for creating coherent light sources with unique capabilities. ~The main challenge for conversion efficiency of processes like frequency doubling is the chromatic dispersion of the nonlinear medium. ~Successful techniques for correcting the phase mismatch between the different frequencies are often limited by the type of nonlinear medium that may be used. ~An all-optical method of quasi-phase matching using counterpropagating light has recently been demonstrated for high-order harmonic generation, an extreme nonlinear process. ~Sequences of counterpropagating pulses are used to interfere with the harmonic generation process periodically, correcting the phase mismatch and boosting efficiency. ~We report progress on an experimental investigation of the effect of counterpropagating light on the more commonly used low-order nonlinear optical processes. ~We present data showing the effects of a single counterpropagating pulse on the efficiency of frequency doubling of a Ti:sapphire ultrafast laser oscillator in beta-Barium Borate. [Preview Abstract] |
|
G1.00128: Phenomenological Modeling for Langmuir Monolayers Dimitri Baptiste, David Kelly, Twymun Safford, Chandra Prayaga, Christopher N. Varney, Aaron Wade Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. [Preview Abstract] |
|
G1.00129: The effect of drainage channels on the hydrodynamic drag of non-colloidal spheres down an inclined plane. Brian Ryu, Charles Dhong, Joelle Frechette While it is well known that surface asperities and roughness alter the hydrodynamic drag of a non-colloidal sphere down an inclined plane, less is known about how the hydrodynamic drag is modified if the asperities and roughness are connected through a network of drainage channels, which allows the movement of fluid between asperities. We investigate the rotational and translation motion of spheres on several pairs of surfaces that have the same porosity and asperity size, but one surface has interconnected drainage channels whereas the other does not. These can have direct relevance to lubricated surfaces such as ball bearings in industrial settings, or biological relevance of leucocyte movement across rough surfaces. [Preview Abstract] |
|
G1.00130: Magnetic and Magnetocaloric Properties in Non-Stoichiometric Gallium Deficient Ni$_2$MnGa$_{1-x}$ Heusler Alloys Alexander Madden, Mollie Corrigan, Linda Barton Magnetic data show that off-stoichiometric gallium deficient Heusler alloys of the form Ni$_2$MnGa$_{1-x}$ have structural martensite transition temperatures that increase strongly with $x$, while their ferromagnetic Curie temperatures remain nearly unchanged. The martensite transition approaches room temperature for $x=0.13$. Samples were prepared by rf induction heating. The influence of quenching and post annealing on magnetic properties, as well as structural grain sizes and magnetic domain structure, were investigated. Since the first order structural phase transition can be adjusted to any convenient temperature, these materials offer intriguing possibilities as magnetic refrigerants. Magnetocaloric properties were investigated by direct measurement of $\Delta T$ with the application of field $\Delta H$. [Preview Abstract] |
|
G1.00131: First-principles study of low-frequency phonon modes in heterostructures of transition metal dichalcogenides Nathan Prins, Danna Doratotaj, Jia-An Yan Transition metal dichalcogenides (TMDs) are layered compounds with weak interlayer interactions and have attracted tremendous attention because of their remarkable electronic, optical and transport properties. Heterostructures made of TMDs offer an additional degree of freedom to tune their electronic properties. In this work, we present a first-principles study of the low-frequency modes in WS$_{2}$/MoS$_{2}$ and WSe$_{2}$/MoSe$_{2}$ heterostructures for various stacking geometry and stacking sequence. Our calculations show that the low-frequency layer shearing modes and layer breathing modes provide a useful way to characterize the stacking geometry of these heterostructures. Finally, the simulated Raman spectra for these heterostructures are discussed. [Preview Abstract] |
|
G1.00132: ABSTRACT WITHDRAWN |
|
G1.00133: Understanding Binding Peptide Design Using a Synthesis of Residue Physicality and Energetic Frustration Lenaya Flowers, Swarnendu Tripathi, Margaret Cheung The ubiquitous nature of Calmodulin (CaM) allows it to bind to numerous peptides, thus altering the function of a protein complex. Variations in CaM’s function are a product of the numerous binding targets (BT) and their significant biological pathways. Given that CaM is a well-studied protein, we have found that certain amino acids in CaM’s sequence play an important role in the event of protein binding. 36 CaM binding targets were analyzed to find sequential, physical commonalities. Using the \textit{Frustrometer} (frustrometer.tk), we obtained z-scores (a numerical value for level of frustration) for each amino acids in a given binding target sequence. From those results, we were able to identify which residues show a highly favorable energetic change after binding and those that do not. We have found charged residues show the most prominent change when bound to CaM, these amino acids may provide a critical role in the overall design and function of a CaM-BT complex. [Preview Abstract] |
|
G1.00134: Weyl semimetal state in TaP: experimental discovery Pavel Shibayev, Su-Yang Xu, Ilya Belopolski, Daniel S. Sanchez, Shuang Jia, Hsin Lin, M. Zahid Hasan Despite their extreme rareness in nature, Weyl semimetals provide the first realization of Weyl fermions. After families of tantalum-based (TaAs, TaP) and niobium-based (NbAs, NbP) compounds were recently predicted as Weyl semimetal candidates, our group experimentally realized the Weyl semimetal state in TaP. Angle-resolved photoemission spectroscopy (ARPES) was used to probe the surface features of TaP. Weyl fermion cones and nodes were directly observed in the bulk, and Fermi arcs were observed on the surface. The surface states were found to possess a rich structure, containing topological Fermi arcs and topologically trivial closed contours in the neighborhood of Weyl points. This finding opens up possibilities to study the relationship between trivial and topological surface states on the surface of a Weyl semimetal. By determining the number of chiral edge modes on a closed path enclosing the Weyl node, bulk-boundary correspondence was demonstrated, leading to the establishment of a topologically nontrivial nature of the Weyl semimetal state in TaP. [Preview Abstract] |
|
G1.00135: The effects of impurities and incidence angle on the secondary electron emission of Ni(110) Hadar Lazar, Marlene Patino, Yevgeny Raitses, Bruce Koel, Charles Gentile, Eliot Feibush The investigation of secondary electron emission (SEE) of conducting materials used for magnetic fusion devices and plasma thrusters is important for determining device lifetime and performance. Methods to quantify the secondary electron emission from conducting materials and to characterize the effects that impurities and incidence angles have on secondary electron emission were developed using 4-grid low energy electron diffraction (LEED) optics. The total secondary electron yield from a Ni(110) surface was continuously measured from the sample current as surface contamination increased from reactions with background gases in the ultrahigh vacuum chamber. Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) were used to examine the composition and impurity levels on the Ni(110) surface. The total secondary electron yield was also measured at different incidence angles. [Preview Abstract] |
|
G1.00136: Frequency and voltage dependence of series resistance in a solar cell Alexander Ogle, Thaddeus Cox, Jennifer Heath While admittance measurements of solar cells are typically conducted in reverse or at zero bias, and analyzed using the depletion approximation, the operating point of the solar cell is in forward bias, and the series resistance is often estimated using IV curves with a high forward current. In this mode, the device is no longer in the depletion regime, and the large number of injected minority carriers alter the transport properties significantly. In our Cu(In,Ga)Se2 devices, we measure negative values of capacitance at high forward bias, which may be linked to injected minority carriers and carrier transport limitations, although our calculations of capacitance may also be influenced by series resistance. In this study, we compare ac and dc measurements of voltage dependent series resistance to try to better understand the negative capacitance signal. [Preview Abstract] |
|
G1.00137: Improving Qubit Quality Factors Through Exotic Materials Victoria Norman In the time since the first qubits were successfully fabricated, the coherence times of superconducting Josephson junction qubits have improved by several orders of magnitude. Yet as the quantum information and computation field moves forward, these coherence times still need further improvement. We are now finding that in some superconducting systems, non-thermal equilibrium quasiparticles are becoming the limiting factor in qubit lifetimes. For SIS superconducting qubits, the T1 and T2* values may be improved by the use of materials with higher superconducting band gap, E$_{\mathrm{G}}$, for which low values may allow for quasiparticles to break up cooper pairs more easily, leading to a shorter lifetime. At this time, Al-Al$_{\mathrm{2}}$Ox$_{\mathrm{3}}$-Al transmons are very well characterized and understood and will therefore serve as an appropriate baseline with which to compare the more exotic junction materials. Using tantalum and niobium, which have E$_{\mathrm{g}}$ values of 3 times and 10 times that of aluminum respectively, we expect the T1 and T2* values to increase significantly for the Al-Al$_{\mathrm{2}}$Ox$_{\mathrm{3}}$-Nb, Al-Al$_{\mathrm{2}}$Ox$_{\mathrm{3}}$-Ta, and Ta-Ta$_{\mathrm{2}}$Ox$_{\mathrm{5}}$-Nb qubits. [Preview Abstract] |
|
G1.00138: Development of a cost effective microscope heater stage Joshua Dugre, Chandra Prayaga, Aaron Wade Utilizing 3D printing technology, a heater stage has been developed and implemented for microscopic systems. Due to the flexibility of 3D printing,the heater stage can be easily modified to fit any sample size with only slight modifications to the heating element being required. The sample in contact with the heating element can also easily be secured in a thermal insulator, such as aluminum foil. The thermal gradient of the heater stage has been recorded to be less than 1$^{\circ}$C and has been compared to more expensive designs, and the cost effectiveness of the system has been determined. The system has been tested with a sample of the liquid crystal 8CB in order to determine the exact temperatures of the phase transitions of the crystal to verify that the system is applicable to a wide range of experimental physics. [Preview Abstract] |
|
G1.00139: Van der Waal Interactions in Ultrafine Nanocellulose Aerogels Byron Fritch, Derek Bradley, Tim Kidd Nanocellulose aerogels have shown an ability to be used in many different applications ranging from oil sponges to conductive materials to possibly a low calorie food substitute. Not much is known about the structural and physical property changes that occur when the composition of the aerogel changes. We studied what properties change when the aerogel amounts change, as well as how sticky the aerogels are and how strong they are. The higher concentrations appeared to have more plate-like structures while the lower concentrations had a more fibrous material. These fibers in the low concentrations had a smaller diameter than a human hair. Only the low concentration aerogels were able to stick to a glass surface in the adhesion test, but were able to support a mass much larger than their own. These low concentrations also would stick to your finger when lightly touched. Preliminary tests show that a concentration that is not too low, but not too high, is best for tensile strength. All concentrations were able to hold many times their own mass. Cellulose should be studied more because it is a renewable material and is easily accessed. Nanocellulose is also not environmentally dangerous allowing it to be used in applications involving humans and the environment like noted above. [Preview Abstract] |
|
G1.00140: ABSTRACT WITHDRAWN |
|
G1.00141: Study of Langmuir and Langmuir-Blodgett Thin films Ross Goodwin, Chandra Prayaga, Aaron Wade Arachidic Acid, Cholesterol, and Stearic Acid thin films were created and studied utilizing the Langmuir method in order to obtain a single molecule or monomolecular layer out of a desired substance at an air-water interface. The phase transitions are observed by measuring the surface pressure vs. area isotherms. Langmuir-Blodgett (LB) films were created on a prepared substrate. The LB film structures were then studied using X-ray Diffraction, and Raman Spectroscopy. [Preview Abstract] |
|
G1.00142: Spatially varying geometric phase in classically entangled vector beams of light Andrew King-Smith, Cody Leary We present theoretical results describing a spatially varying geometric (Pancharatnam) phase present in vector modes of light, in which the polarization and transverse spatial mode degrees of freedom exhibit classical entanglement. We propose an experimental setup capable of characterizing this effect, in which a vector mode propagates through a Mach-Zehnder interferometer with a birefringent phase retarder present in one arm. Since the polarization state of a classically entangled light beam exhibits spatial variation across the transverse mode profile, the phase retarder gives rise to a spatially varying geometric phase in the beam propagating through it. When recombined with the reference beam from the other interferometer arm, the presence of the geometric phase is exhibited in the resulting interference pattern. [Preview Abstract] |
|
G1.00143: Deterministic and Stochastic Modeling of an Artificial Bistable Switch in E. coli Daniel Finkelstein, Nicolas Buchler, Sargis Karapetyan Networks of mutually interacting genes are common in natural regulatory networks. To better understand these interactions, scientists have recently been constructing artificial genetic networks. Much of the effort is focused on creating genetic oscillators and bistable switches. In this project, we analyzed the possibility to create a bistable switch in E. coli. In this realization of the switch, the Repressor (basic leucine zipper CEBP/alpha) represses the transcription of the Inhibitor (artificial dominant negative 3HF). The Inhibitor, in turn, sequesters the Repressor by binding to it. Using deterministic modeling we identified a range of parameters suitable for bistability. We then analyzed the resulting solutions with the full model taking the reaction rates corresponding to E. coli and the including stochastic nature of gene expression. We have shown that the bistability in not destroyed by stochastic fluctuations if several copies of genes are present. Specifically, taking a realistic number of plasmids (10) we show that the number of proteins in the systems undergoes sizable fluctuations; however, the two states with low and high concentrations of inhibitor stay distinct in the relevant range of parameters. [Preview Abstract] |
|
G1.00144: Alpha Background Rejection in Bolometer Detectors Nicholas DePorzio This study presents the modification of bolometer detectors used in particle searches to veto or otherwise reject alpha radiation background and the statistical advantages of doing so. Several techniques are presented in detail -- plastic film scintillator vetoes, metallic film ionization vetoes, and Cherenkov radiation vetoes. Plastic scintillator films are cooled to bolometer temperatures and bombarded with 1.4MeV to 6.0MeV alpha particles representative of documented detector background. Quantum dot based liquid scintillator is similarly bombarded to produce a background induced scintillation light. Photomultipliers detect this scintillation light and produce a veto signal. Layered metallic films of a primary metal, dielectric, and secondary metal, such as gold-polyethylene-gold films, are cooled to milli-kelvin temperatures and biased to produce a current signal veto when incident 1.4MeV to 6.0MeV alpha particles ionize conduction paths through the film. Calibration of veto signal to background energy is presented. These findings are extrapolated to quantify the statistical impact of such modifications to bolometer searches. Effects of these techniques on experiment duration and signal-background ratio are discussed. [Preview Abstract] |
|
G1.00145: Green Chemistry Techniques for Gold Nanoparticles Synthesis Sarah A. Cannavino, Christy A. King, Davon W. Ferrara Gold nanoparticles (AuNPs) are often utilized in many technological and research applications ranging from the detection of tumors, molecular and biological sensors, and as nanoantennas to probe physical processes. As these applications move from the research laboratory to industrial settings, there is a need to develop efficient and sustainable synthesis techniques. Recent research has shown that several food products and beverages containing polyphenols, a common antioxidant, can be used as reducing agents in the synthesis of AuNPs in solution. In this study, we explore a variety of products to determine which allow for the most reproducible solution of nanoparticles based on the size and shapes of particles present. We analyzed the AuNPs solutions using extinction spectroscopy and atomic force microscopy. We also develop a laboratory activity to introduce introductory chemistry and physics students to AuNP synthesis techniques and analysis. [Preview Abstract] |
|
G1.00146: Solvent vapor induced morphology variation in thin films of PS-b-PLA copolymers Lauren Foote, Maximilian Heres, Thomas Kinsey, Joshua Sangoro Molecular dynamics in thin films of PS-b-PLA copolymers annealed by solvent vapor annealing is investigated using broadband dielectric spectroscopy, atomic force microscopy and ellipsometry. Impact of morphology changes on molecular dynamics are analyzed. The results of this study are discussed within the framework of current understanding of morphology control of copolymer thin films. [Preview Abstract] |
|
G1.00147: Optical Properties of Silver Nanoparticulate Glasses Rachel N. Evans, Sarah A. Cannavino, Christy A. King, Joseph A. LaMartina, Robert H. Magruder, Davon W. Ferrara The ion exchange method of embedding metal nanoparticles (NPs) into float glass is an often used technique of fabricating colored glasses and graded-index waveguides. The depth and size of NP formation in the glass depends on the concentration and temperature of metal ions in the molten bath. In this study we explore the dichroic properties of silver metal ion exchange restricted to only one side of a glass microscope slide using reflection and transmission spectroscopy and its dependence on temperature, concentration of silver ions, and length of time in the molten bath. [Preview Abstract] |
|
G1.00148: Simulation of Thin Film Equations on an Eye-Shaped Domain with Moving Boundary Joseph Brosch, Tobin Driscoll, Richard Braun During a normal eye blink, the upper lid moves, and during the upstroke the lid paints a thin tear film over the exposed corneal and conjunctival surfaces. This thin tear film may be modeled by a nonlinear fourth-order PDE derived from lubrication theory. A major stumbling block in the numerical simulation of this model is to include both the geometry of the eye and the movement of the eyelid. Using a pair of orthogonal and conformal maps, we transform a computational box into a rough representation of a human eye where we proceed to simulate the thin tear film equations. Although we give up some realism, we gain spectrally accurate numerical methods on the computational box. We have applied this method to the heat equation on the blinking domain with both Dirichlet and no-flux boundary conditions, in each case demonstrating at least 10 digits of accuracy.. We are able to perform these simulations very quickly (generally in under a minute) using a desktop version of MATLAB. [Preview Abstract] |
|
G1.00149: \textbf{Constructing Dual Beam Optical Tweezers for Undergraduate Biophysics Research} Brian Daudelin, Devon West-Coates, Jon del'Etoile, Eric Grotzke, Thayaparan Paramanathan Optical tweezing, or trapping, is a modern physics technique which allows us to use the radiation pressure from laser beams to trap micron sized particles. Optical tweezers are commonly used in graduate level biophysics research but seldom used at the undergraduate level. Our goal is to construct a dual beam optical tweezers for future undergraduate biophysical research. Dual beam optical tweezers use two counter propagating laser beams to provide a stronger trap. In this study we discuss how the assembly of the dual beam optical tweezers is done through three main phases. The first phase was to construct a custom compressed air system to isolate the optical table from the vibrations from its surroundings so that we can measure pico-newton scale forces that are observed in biological systems. In addition, the biomaterial flow system was designed with a flow cell to trap biomolecules by combining several undergraduate semester projects. During the second phase we set up the optics to image and display the inside of the flow cell. Currently we are in the process of aligning the laser to create an effective trap and developing the software to control the data collection. This optical tweezers set up will enable us to study potential cancer drug interactions with DNA at the single molecule level and will be a powerful tool in promoting interdisciplinary research at the undergraduate level. [Preview Abstract] |
|
G1.00150: Landau Damping in a Mixture of Bose and Fermi Superfluids Huitao Shen, Wei Zheng We study Landau damping in Bose-Fermi superfluid mixture at finite temperature. We find that at low temperature, the Landau damping rate will be exponentially suppressed at both the BCS side and the BEC side of Fermi superfluid. The momentum dependence of the damping rate is obtained, and it is quite different from the BCS side to the BEC side. The relation between our result and the collective mode experiment in recently realized Bose-Fermi superfluid mixture is also discussed. [Preview Abstract] |
|
G1.00151: PHYSICS EDUCATION |
|
G1.00152: The Physics of Quidditch Summer Camp: An Interdisciplinary Approach Donna Hammer, Tim Uher The University of Maryland Physics Department has developed an innovative summer camp program that takes an interdisciplinary approach to engaging and teaching physics.~ The Physics of Quidditch Camp uniquely sits at the intersection of physics, sports, and literature, utilizing the real-life sport of quidditch adapted from the Harry Potter novels to stimulate critical thinking about real laws of physics and leaps of imagination, while actively engaging students in learning the sport and discussing the literature. Throughout the camp, middle school participants become immersed in fun physics experiments and exciting physical activities, which aim to build and enhance skills in problem-solving, analytical thinking, and teamwork.~ This camp has pioneered new ways of teaching physics to pre-college students, successfully engaged middle school students in learning physics, and grown a large demand for such activities. [Preview Abstract] |
|
G1.00153: Peer Grading in Astronomy Massive Open Online Course Martin Formanek, Matthew Wenger, Christopher Impey, Sanlyn Buxner In this work we thoroughly investigate the peer grading process as it happened in the University of Arizona session based MOOC “Astronomy: Exploring Time and Space” offered during Spring 2015 through Coursera. Overall, 25400 learners from over 100 countries registered for this course. Of those, 14900 accessed at least one part of the course and 1332 users engaged in the peer grading. First of all we provide description of the peer graded assignments and we identify trends in behavior of people who participated in these exercises. E.g. time they spent on grading, number of assignments graded and patterns arising from comparing all three assignments. Furthermore, for the second assignment, we graded random sample of 300 essays by a group of trained undergraduate students and a group consisting of one of the course instructors together with graduate TAs and we compared results with grades from the peer grading. Specifically we look on Intraclass Correlation Coefficients for all three groups of graders to determine reliability of each group and correlations between final grades. Finally we assess factors influencing reliability of the peer graders participating in the MOOC based on the difference from our grades. [Preview Abstract] |
|
G1.00154: Roadrunner physics: using cartoons to challenge student preconceptions Rachael Huxford, Mathew Ridge, James Overduin, Jim Selway The cartoon universe is governed by laws that differ radically from those in the real world, but also mirror some of our preconceptions of how the world ``should'' work. We all know that Wile E. Coyote will never be able to catch the Roadrunner with a fan attached to a sailboard, or an outboard motor submerged in a pail of water---but \textit{why}, exactly? Can we attach some numbers to this knowledge? We have designed some classroom demonstrations accompanied by personal-response-type questions that use classic cartoon clips to challenge student thinking in introductory courses, prompting them to rediscover the truths of physics for themselves. We extend this idea to intermediate-level modern physics, showing that some phenomena in the cartoon universe can be reconciled with standard physics if the values of fundamental constants such as $c, G$ and $h$ differ radically from those in the real world. Such an approach can both heighten student interest and deepen understanding in various physics topics. [Preview Abstract] |
|
G1.00155: The Hunt for Red October II: a demonstration for introductory electromagnetism Daniel Zile, Thomas Sebastian, Viktor Polyak, Anjalee Rutah, James Overduin We have designed, constructed and tested a small-scale version of the silent submarine depicted in the 1990 Sean Connery thriller \textit{The Hunt for Red October}. This vessel contains no moving parts. It uses onboard batteries and magnets to propel seawater salt ions out of the back of the boat, producing an equal and opposite forward thrust on the submarine thanks to Newton's third law. Such a craft could be very hard to detect by conventional means. Our objectives were to create a striking teaching demonstration for introductory electromagnetism courses and to determine why (to our knowledge) no navy has yet exploited such a seemingly revolutionary propulsion system for purposes of national defense. As teaching demonstrations, our prototypes are very successful at capturing student interest and convincing them of the reality and practical importance of electromagnetic fields. We have also identified a number of factors that may help to explain why a scaled-up model might not quite function as depicted in the film. We discuss several promising avenues for future student research. [Preview Abstract] |
|
G1.00156: \textbf{Enhancing Student Success in Biology, Chemistry, and Physics by Transforming the Faculty Culture} Howard Jackson, Leigh Smith, Kathleen Koenig, Jill Beyette, Brian Kinkle, Anne Vonderheide We present preliminary results of an effort to enhance undergraduate student success in the STEM disciplines. We explore a multistep approach that reflects recent literature and report initial results by each of the Departments of Biology, Chemistry, and Physics of implementing several change strategies. The central elements of our approach involve identified departmental Teaching and Learning Liaisons, a unique faculty development component by our teaching center, a vertical integration of leadership across department heads, the Dean, and the Provost, and the explicit acknowledgement that change happens locally. Teaching and Learning lunches across the departments have attracted an attendance of \textasciitilde 65{\%} of the faculty. The use of Learning Assistants in classrooms has also increased sharply. Modest changes in the student success rates have been observed. These efforts and others at the decanal and provostal levels promise changes in student success. [Preview Abstract] |
|
G1.00157: \textbf{Students' Attitudes and Enrollment Trends in Physics and Engineering} Delphine Banjong \textbf{S}cience, \textbf{T}echnology, \textbf{E}ngineering, and \textbf{M}athematics (\textbf{STEM}) fields are critical for meeting ever-increasing demands in the U.S. for STEM and related skills, and for ensuring the global competitiveness of the United States in technological advancement and scientific innovation. Nonetheless, few U.S. students consider a STEM degree after high school and fewer STEM students end up graduating with a STEM degree. In 2012, the United States ranked 35$^{th}$ in~math and 27$^{th}$ in science out of 64 participating countries in the Program for International Student Assessment (PISA), sponsored by the Organization for Economic Cooperation and Development (OECD). Considering the significant role physics and engineering play in technological advancement, this work investigates the attitudes of students and recent enrollment trends in these important subject areas. [Preview Abstract] |
|
G1.00158: OUTREACH AND ENGAGING THE PUBLIC |
|
G1.00159: The World's Biggest Movie Theater: Promoting the Stars Arthur Pallone, Jacque Day-Pallone A great celestial story is only as effective as the teller of the tale. With passion and knowledge at the helm, we must search for ways to pass on that enthusiasm to others while conveying sound science. At the core, our common link is an age-old awe of the sky. From the scientist to the elementary school student, we ask remarkably similar questions. What's out there? When will some object slam into the Earth? Are we alone? In our view as advocates for astronomy at the community level, the public will emerge to discover answers to their questions, if given the forum. It's our responsibility as astronomy advocates to help one another provide those forums. While some regions, perhaps through a school or by a turn of good fortune, offer public observatories with sophisticated telescopes, we also know that an observing event can take place in an open field or a parking lot, and be fully palpable as seen through a pair of binoculars, or by the naked eye. Based on our experience, we present an integrated approach---one that borrows elements from education, entertainment, advertising, and public relations--to help choose an event, hook and keep the public's attention while making them want more, and provide some tips for increasing media presence. [Preview Abstract] |
|
G1.00160: INTERNATIONAL ISSUES |
|
G1.00161: The African Synchrotron Light Source (AfLS) Sekazi Mtingwa, Ahmadou Wague, Simon Connell, Brian Masara, Tshepo Ntsoane, Lawrence Norris, Herman Winick, Kenneth Evans-Lutterodt, Tabbetha Dobbins, Tarek Hussein, Feene Maresha, Krystle McLaughlin, Philip Oladijo, Esna du Plessis, Romain Murenzi, Kennedy Reed, Francesco Selte, Sverker Werin, Jonathan Dorfan, Mohammad Yousef Africa is the only habitable continent without a synchrotron light source. An interim Steering Committee held a major conference on November 16-20, 2015 at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France to bring together African scientists, policy makers, and stakeholders to discuss the possibility of a synchrotron light source in Africa. The use of light sources as a premier tool for research was highlighted for a broad range of disciplines. A Roadmap towards a synchrotron in Africa was discussed. Firm outcomes of the Conference were a set of Resolutions and a Roadmap document, with the election of a Steering Committee. (www.africanlightsource.org). [Preview Abstract] |
|
G1.00162: HISTORY OF PHYSICS |
|
G1.00163: The Discovery of Electrography. Larissa Samuilova, Vladimir Samuilov Prof. Jakob Narkiewicz-Jodko (1947--1905) major discoveries are: Electrography -- the method of the visualization of corona discharge (corona discharge photography) from the bodies due to the application of high strength and high frequency electric fields [1-4], and the first observation of the propagation of the electromagnetic waives for information transfer over the distances [5,6]. They were made in his laboratory, located at his manor home Nadniemen in Eastern Europe. We describe these experiments and equipment used in the Lab for these discoveries. We also introduce a mathematical algorithm for the analysis of the electrography images. [1] Decrespe M. La vie et les oeuvres de M. de Narkiewicz-Iodko, member et collaborateur de l'Institut imperial de medecineexperimentale de Saint-Petersbourg, member of correspondent de la Societe de Medecine de Paris, etc./ Marius Decrespe.- Paris, Chamuel, 1896, 51p. [2] Annalen der Physik.- Leipzig, 1896. -- Bd 293, 132 [3] Electrography// The Photographic news for amateur photographers.- 1896.- vol. 40, p.450 [4] Maack F. Elektrographie. Mit besonderer Berucksich-tigung der Versuche Narkiewicz-Jodko/ Ferdinand Maack// Wissenseschaltliche Zeitschrift\textellipsis -- 1898.- Bd 1, 1, 8-22; -1898.- Bd 1, 2/3, 89-99. [5] S\'{e}ances de la societe francaise de physique/ Societe francaise de physique. -- Paris, 1898, p. 77-79. [6] Present condition of wireless telegraphy// Consular reports: Commerce, manufacturers, etc. of their consular districts. Bureau of Foreign Commerce of United States.- Washington 1901, v.66. p. 44. [Preview Abstract] |
|
G1.00164: SUPERLATTICES, NANOSTRUCTURES, AND OTHER ARTIFICIALLY STRUCTURED MATERIALS |
|
G1.00165: Thermite Reaction to Produce Artificial Reefs Alexandro Trevino, Karen Martirosyan, Richard Kline The degradation of coral reefs is an ecological issue that has prompted new collaboration by different scientific communities that would assist in the regeneration of the reefs. Unfortunately, these processes can be inefficient and extremely expensive prompting a new scientific approach by using solid-state combustion synthesis to regenerate the reefs. ~In this report we aimed to consolidate a multi-composite material to produce artificial reefs by initiating thermite reaction based on aluminum and polytetrafluoroethylene (PTFE) with natural reefs. By Thermodynamic analysis and experimentation it was established that a range between .03-.07 number of moles of PTFE was sufficient to reach an adiabatic temperature of over 1900 K, a sustained reaction and a physically stable product was achieved.~ Reefs are primarily composed of carbonates but their exact chemical composition can vary. X-ray diffraction analysis was used to determine the chemical composition of the reef and revealed presence of oxides, carbonates, silicates. The dominant~chemical compounds that~were identified are, SiO2 -17{\%}, MgSiO3-14.5{\%}, CaCO3- 11.4{\%}, Ca(Si3O4). Using our thermite reaction we aimed to achieve optimal physical, chemical, and biological properties and maintain cost efficiency of the multi-composite material.~ [Preview Abstract] |
|
G1.00166: Synthesis and Characterization of ZnS:Eu$^{\mathrm{3+}}$ - CMC nanophosphors emitting white light over broad excitation range Dilip De, Ikorya Ahemen, Viena Bruno In this paper we report for the first time the synthesis and characterization of nanophosphors of ZnS:Eu$^{\mathrm{3+}}$ - embedded in sodium carboxymethyl cellulose matrix (CMC) that emits high quality white light over broad range of excitation. The nano-phosphors of cubic (zinc blende) structure were synthesized using precipitation technique with doping concentrations of Eu$^{\mathrm{3+}}$ ions 1 mol{\%} and 5 mol{\%}. The crystal sizes were 2.56 nm and 2.91 nm respectively. Annealing at 300 $^{\mathrm{o}}$C in a sulfur-rich atmosphere altered the crystal size to 4.35 nm and 3.65 nm respectively and the band gap from 4.2 eV to 3.76 eV and 3.81 eV respectively. The as-synthesized samples gave pure orange-red emission when excited at wavelengths of 394 nm and 465 nm. After thermal annealing of the samples, a broad emission band in the blue-green region assigned to defect related states emerged or were enhanced. Also enhanced were the emission lines of Eu$^{\mathrm{3+}}$ ions in the orange-red region. A combination of these two transitions gave white light of different shades (recorded on the CIE 1931 chromaticity diagram) from cool white through Day-light to warm white light, depending on Eu$^{\mathrm{3+}}$ concentration and the excitation wavelengths (UV-330 to blue 465 nm), thus showing great potential applications of these nano-phosphors. [Preview Abstract] |
|
G1.00167: Thermally Engineered Blue Photoluminescence of Porous Anodic Alumina Membranes for Promising Optical Biosensors Sang Don Bu, Sam Yeon Cho, Yong Chan Choi, Jin Woo Kim, Jin Kyu Han, Jin Ho Kwak, Sun A Yang Optical biosensors based on porous anodic alumina membranes (PAAMs) have shown to be an effective device because of their unique optical properties and biocompatibility. Among various optical properties, photoluminescence (PL) emission derived from PAAMs is one of the most suitable characteristics. However, the origin of PL from PAA is unclear and still in doubt. Therefore, it is essential for further potential practical applications to understand the origin of PL and PL variations. Here, we investigate the effects of post-annealing temperatures on the blue PL of amorphous PAAMs fabricated in oxalic acid. We find that the blue PL emission is strongly dependent on the thermal properties. A strong blue PL at a peak of \textasciitilde 460 nm is observed from the initial PAAM (not annealed PAAM) and this PL band can be divided into two Gaussian components at 458$\sim\pm\sim$4 nm (P1 band) and 517$\sim\pm$ 7nm (P2 band). As the temperature increases to 600 $^{\circ}\mathrm{C}$, the intensities of two PL bands gradually increase. During temperature increases from 600 to 700 $^{\circ}\mathrm{C}$, the P2 band increases but the P1 band decreases. The analyses of electron paramagnetic resonance, Fourier transform infrared spectroscopy, and ultraviolet-visible absorption spectroscopy show that the P1 and P2 bands originate from the unstable carboxylates and the stable carboxylates, respectively. [Preview Abstract] |
|
G1.00168: Imaging TiO$_{\mathrm{2}}$ nanoparticles on GaN nanowires with electrostatic force microscopy Ting Xie, Baomei Wen, Guannan Liu, Shiqi Guo, Abhishek Motayed, Thomas Murphy, R.D. Gomez Gallium nitride (GaN) nanowires that are functionalized with metal-oxides nanoparticles have been explored extensively for gas sensing applications in the past few years. These sensors have several advantages over conventional schemes, including miniature size, low-power consumption and fast response and recovery times. The morphology of the oxide functionalization layer is critical to achieve faster response and recovery times, with the optimal size distribution of nanoparticles being in the range of 10 to 30 nm. However, it is challenging to characterize these nanoparticles on GaN nanowires using common techniques such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Here, we demonstrate electrostatic force microscopy in combination with atomic force microscopy as a non-destructive technique for morphological characterization of the dispersed TiO$_{\mathrm{2}}$ nanoparticles on GaN nanowires. We also discuss the applicability of this method to other material systems with a proposed tip-surface capacitor model. [Preview Abstract] |
|
G1.00169: Management of the von Roos operator. Martin Molinar-Tabares, Lamberto Castro-Arce, Carlos Figueroa-Navarro, Julio Campos-Garcia When an electron is inside a semiconductor medium its effective mass rises from the shielding of the crystalline structure. When we have a semiconductor with a constant concentration the effective mass has a fixed value, and in this case, it can be easy to solve the Schrodinger equation of the particle, but if the concentration varies spatially, the effective mass will no longer constant and the solution can be difficult to find. The general form of the kinetic energy operator for a particle with variable mass is proposed for von Roos, this operator is characterized by some parameters whose values are subjected to a restriction. From a numerical solution of the Schrodinger equation we analyze the energies of an electron with position-dependent effective mass working with some values of the parameter of the von Roos operator. [Preview Abstract] |
|
G1.00170: Oscillation modes and transmission into a Fibonacci slab. Lamberto Castro-Arce, Martin Molinar-Tabares, Julio Campos-Garcia, Carlos Figueroa-Navarro, Leonardo Isasi-Siqueiros, Betsabe Manzanares-Martinez In our contribution we developed a study on the behavior of the transmission modes and a Pt / Zn slab of a Fibonacci array of longitudinal and transverse acoustic waves. We have worked with arrangements from n $=$ 1 to10 and has managed to find the energy bands and transmission, filling factor 0.4 observing the appearance of Pseudo-Gaps in the evolution of the study when the arrangement Fibonacci increases. [Preview Abstract] |
|
G1.00171: Shedding Light on the Formation of Gold Nanorods Orlando Lopez, Damien Hudry, Dmytro Nykypanchuk A significant interest in the study and synthesis of one-dimensional materials such as nanorods or nanowires is sparked by their potential application in electronics, photonics and biodetection. However, the synthesis of these low dimensional materials is not always reliable due to kinetic effects in symmetry breaking and high sensitivity to impurities. In this work we discuss the synthesis of gold nanorods and new ways to achieve symmetry breaking during the growth from seed solution, hence maximizing the yield of nanorods. We discuss the mechanism involved in symmetry breaking and general strategies to improve the nanorod morphology and synthetic yield. This work can serve as a starting point to design reproducible synthetic strategies for preparing high quality gold nanorods. [Preview Abstract] |
|
G1.00172: Exciton Emission from Bare and Alq$_{\mathrm{3}}$/Gold Coated GaN Nanorods Fatemesadat Mohammadi, Gerd Kuhnert, Detlef Hommel, Heidrun Schmitzer, Hans-Peter Wagner We study the excitonic and impurity related emission in bare and aluminum quinoline (Alq3)/gold coated wurtzite GaN nanorods by temperature-dependent time-integrated (TI) and time-resolved (TR) photoluminescence (PL). The GaN nanorods were grown by molecular beam epitaxy. Alq3 as well as Alq3/gold covered nanorods were synthesized by organic molecular beam deposition. In the near-band edge region a donor-bound-exciton (D$^{\mathrm{0}}$X) emission is observed at 3.473 eV. Another emission band at 3.275 eV reveals LO-phonon replica and is attributed to a donor-acceptor-pair (DAP) luminescence. TR PL traces at 20 K show a nearly biexponential decay for the D$^{\mathrm{0}}$X with lifetimes of approximately 180 and 800 ps for both bare and Alq3 coated nanorods. In GaN nanorods which were coated with an Alq$_{\mathrm{3}}$ film and subsequently with a 10 nm thick gold layer we observe a PL quenching of D$^{\mathrm{0}}$X and DAP band and the lifetimes of the D$^{\mathrm{0}}$X transition shorten. The quenching behaviour is partially attributed to the energy-transfer from free excitons and donor-bound-excitons to plasmon oscillations in the gold layer. [Preview Abstract] |
|
G1.00173: Role of polymers and surfactants in synthesis of high quantum yield upconverting nanoparticles. Kevin Newcombe, Brian Yust Rare earth doped fluoride nanoparticles with a size of about 25 nm have been synthesized by either solvothermal or microwave assisted techniques. The role of differing biocompatible polymeric compounds to act as nucleation agents and surfactants, including polyethylene glycol, polyvinylpyrollidone, and polyethylene oxide, in the final size, crystallinity, and optical properties is investigated in depth. These upconverting nanoparticles which can be excited in the near-infrared (NIR) are ideal for biomedical applications because of the low absorption of these excitation wavelengths by soft tissues in the body. Their fluorescence can be used for NIR imaging as well as non-invasive activation of drugs conjugated to the surface for cancer therapy. After optimizing the synthesis parameters, wide angle x-ray diffraction, FTIR, Raman, and Vis-NIR spectroscopy are used to characterize the samples. By varying the polymer added to the precursor solution, we can elucidate the primary mechanisms of interaction during the synthesis process and optimize for the best possible optical properties. Finally, the dependence of the fluorescence intensity on the biocompatible polymer type and concentration will also be investigated. [Preview Abstract] |
|
G1.00174: Diagnostics of defects in AlGaN/GaN high electron mobility transitor (HEMT) epi-layers via spectroscopic photo current-voltage (IV) measurements with variable-wavelength ultraviolet (UV) and visible light excitation. Min P. Khanal, Burcu Ozden, Vahid Mirkhani, Kosala Yapabandara, Muhammad Shehzad Sultan, Minseo Park, Li Shen The reliability and performance of the nitride high electron mobility transistors (HEMTs) have been plagued by deleterious phenomena such as current collapse which is believed to be produced by electrically-active deep-level defects (or traps) that reside at the surface/interfaces and in the bulk of the AlGaN/GaN HEMT layers. Therefore, identification of their physical/spectral locations and understanding the nature of defects is very important to improve the reliability of AlGaN/GaN HEMTs. In this work, deep-level defects and traps located in the AlGaN/GaN HEMT epi-layers were investigated by using spectroscopic photo IV measurements. An array of Schottky contacts was constructed on the HEMT layer produced by metal-organic chemical vapor deposition (MOCVD). The photo IV measurement was performed by collecting the photo current generated by the variable-wavelength UV/visible light illumination. It was successfully demonstrated that this technique can provide the information on the distribution of electrically-active defects along the in-depth direction and across the HEMT wafers. Therefore, it can be concluded that the spectroscopic measurements can be useful to assess the uniformity of defect distribution both along the in-depth direction and across the AlGaN/GaN wafers. [Preview Abstract] |
|
G1.00175: Multifrequency scanning probe microscopy study of nanodiamond agglomerates Vasudeva Aravind, Stephen Lippold, Qian Li, Evgheny Strelcov, Baris Okatan, Benjamin Legum, Sergei Kalinin Due to their rich surface chemistry and excellent mechanical properties and non-toxic nature, nanodiamond particles have found applications such as biomedicine, tribology and lubrication, targeted drug delivery systems, tissue scaffolds and surgical implants. Although single nanodiamond particles have diameters about 4-5nm, they tend to form agglomerates. While these agglomerates can be useful for some purposes, many applications of nanodiamonds require single particle, disaggregated nanodiamonds. This work is oriented towards studying forces and interactions that contribute to agglomeration in nanodiamonds. In this work, using multifrequency scanning probe microscopy techniques, we show that agglomerate sizes can vary between 50-100nm in raw nanodiamonds. Extremeties of particles and Interfaces between agglomerates show dissipative forces with scanning probe microscope tip, indicating agglomerates could act as points of increased adhesion, thus reducing lubricating efficiency when nanodiamonds are used as lubricant additives. [Preview Abstract] |
|
G1.00176: Comparison of photoluminescence properties of HSA-protected and BSA-protected Au$_{\mathrm{25}}$ nanoclusters Masato Tsukamoto, Hideya Kawasaki, Tadashi Saitoh, Mitsuru Inada Gold nanoclusters (NCs) have attracted great interest for a wide range of applications. In particular, red light-emitting Au$_{\mathrm{25}}$ NCs have been prepared with various biological ligands. It has been shown that Au$_{\mathrm{25}}$ NCs have Au$_{\mathrm{13}}$-core/6Au$_{\mathrm{2}}$(SR)$_{\mathrm{3}}$-semiring structure. The red luminescence thought to be originated from both core (670 nm) and semiring (625 nm). It is important to reveal a structure of Au$_{\mathrm{25}}$ NCs to facilitate the progress of applications. However, the precise structure of Au$_{\mathrm{25}}$ NCs has not been clarified. There is a possibility of obtaining structural information about Au$_{\mathrm{25}}$ NCs to compare optical properties of the NCs that protected by slightly different molecules. Bovine and human serum albumin (BSA, HSA) are suitable one for this purpose. It has been suggested that rich tyrosine and cysteine residues in these molecules are important to produce the thiolate-protected Au NCs. If Au$_{\mathrm{25}}$ NCs have core/shell structure, only the luminescence of the semiring will be affected by the difference of the albumin molecules. We carefully compared PL characteristics of BSA- and HSA- protected Au$_{\mathrm{25}}$ NCs. As a result, there was no difference in the PL at 670 nm (core), while differences were observed in the PL at 625 nm (semiring). The results support that Au$_{\mathrm{25}}$ NCs have core/semiring structure. [Preview Abstract] |
|
G1.00177: Simulations of terahertz pulse emission from thin-film semiconductor structures Andrey Semichaevsky The photo-Dember effect is the formation of transient electric dipoles due to the interaction of semiconductors with ultrashort optical pulses. Typically the optically-induced dipole moments vary on the ns- or ps- scales, leading to the emission of electromagnetic pulses with terahertz (THz) bandwidths. One of the applications of the photo-Dember effect is a photoconductive dipole antenna (PDA). This work presents a computational model of a PDA based on Maxwell's equations coupled to the Boltzmann transport equation. The latter is solved semiclassically for the doped GaAs using a continuum approach. The emphasis is on the accurate prediction of the emitted THz pulse shape and bandwidth, particularly when materials are doped with a rare-earth metal such as erbium or terbium that serve as carrier recombination centers. Field-dependent carrier mobility is determined from particle-based simulations. Some of the previous experimental results [1] are used as a basis for comparison with our model. [1] J. O'Hara, J.M.O. Zide, A.C. Gossard, A.J Taylor, R.D. Averitt, ``Enhanced Terahertz Detection via ErAs:GaAs nanoisland superlattices'', Applied Physics, 88, 251119, 2006. [Preview Abstract] |
|
G1.00178: Nonlocal spin-confinement of electrons in graphene with proximity exchange interaction Yee Sin Ang, Shi-Jun Liang, Kelvin J. A. Ooi, Chao Zhang, Zhongshui Ma, Lay Kee Ang In graphene-magnetic-insulator hybrid structure such as graphene-Europium-oxide (EuO-G), proximity induced exchange interaction opens up a spin-dependent bandgap and spin splitting in the Dirac band. We study the bound state formation in a hetero-interface composed of EuO-G. We theoretically predict a remarkable nonlocal spin-confinement effect in EuO-G and show that spin-polarized quasi-1D electron interface state can be generated in a magnetic-field-free channel. Quasiparticle transport mediated by the interface state can be efficiently controlled by the channel width and electrostatic gating. Our results suggest a pathway to further reduce the dimensionality of graphene quasiparticles from 2D to 1D, thus offering an exciting graphene-based platform for the search of exotic 1D physics and spintronic applications. [Preview Abstract] |
|
G1.00179: The electronic and transport properties of monolayer transition metal dichalcogenides: a complex band structure analysis Dominik Szczesniak Recently, monolayer transition metal dichalcogenides have attracted much attention due to their potential use in both nano- and opto-electronics. In such applications, the electronic and transport properties of group-VIB transition metal dichalcogenides ($MX_2$, where $M$=Mo, W; $X$=S, Se, Te) are particularly important. Herein, new insight into these properties is presented by studying the complex band structures (CBS's) of $MX_2$ monolayers while accounting for spin-orbit coupling effects. By using the symmetry-based tight-binding model a nonlinear generalized eigenvalue problem for CBS's is obtained. An efficient method for solving such class of problems is presented and gives a complete set of physically relevant solutions. Next, these solutions are characterized and classified into propagating and evanescent states, where the latter states present not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gaps, which describe the tunneling currents in the $MX_2$ materials. The importance of CBS's and tunneling currents is demonstrated by the analysis of the quantum transport across $MX_2$ monolayers within phase field matching theory. [Preview Abstract] |
|
G1.00180: Shot noise in quantum dots in presence of Fano and Dicke effects in Kondo regime Pedro Orellana, Natalia Cortes, Victor Apel The quantum dots allow studying systematically quantum-interference effects as Fano and Dicke effects due to the possibility of continuous tuning the relevant parameters governing the properties of these resonances, in equilibrium and nonequilibrium regimes. The condition for the Fano resonance is the existence of two scattering channels: a discrete level and a broad continuum band. On the other hand, the electronic version of the Dicke effect is analogous to the Dicke effect in optics, which takes place in the spontaneous emission of two closely-lying atoms radiating a photon into the same environment. In quantum dots this effect is due to quantum interference in the passage of an electron through two closely lying resonant states of the quantum dots coupled to common leads. In this work, we present a systematic investigation of the influence of the Dicke effect on shot-noise and Fano factor in a cross-shaped quantum dot array. The relevant quantities are obtained by the non-equilibrium Green’s function technique. Our results show that at zero temperature, the electrical current, shot-noise and Fano factor exhibit characteristics of the Dicke effect. [Preview Abstract] |
|
G1.00181: Self assembly and optical properties of CdSe nanoplatelet superlattice Yunan Gao, William Tisdale Colloidal CdSe nanoplatelets (NPs) are 1-D confined materials with atomic uniform thickness, and only have homogeneous broadening in energy level distributions and very narrow emission spectrum. Additionally, NPs have a giant oscillator strength that leads to a faster emission rate compared to quantum dots and rods. Due to these properties, NPs have shown promising potential applications in light-emitting diodes, colloidal lasers, and harvesting multiple exciton generation in photovoltaic cells.\\ Self-assembly of superlattice has been studied broadly for many nano-particles, but not yet for CdSe NPs. We will show for the first time a selective control of CdSe NP superlattice self-assembly, i.e., self-assembled into columnar or lamellar superlattice. Moreover, we will present that the assembly morphology of superlattice has direct effects on their optical properties, like polarization, absorption efficiency and emission rate, etc., and also on their Forster energy transfer properties. The self-assembly is based on liquid interfacial self-assembly and transfer technique. The structure and propertied of the superlattice are characterized by transmission electron microscopy, and time-, polarization- and space-resolved photo-luminescent micro-spectroscopy. [Preview Abstract] |
|
G1.00182: Novel Application of Cluster Analysis to Transport Data in Single Molecule Break Junctions Ben Wu, Jeffrey Ivie, Tyler Johnson, Roland Himmelhuber, Oliver Monti Single molecule based devices represent the ultimate limit in device design, but uncovering the major factors that determine energy level alignment in single molecule junctions and their effect on the charge transport properties of single molecules is still a major challenge. Analysis of break junction data using a novel density based hierarchical clustering algorithm reveals the deep structure of the highly stochastic data that will help hypothesis-driven elucidation of some of the key parameters for quantum transport. The strength of this approach is its scale-invariance and the identification of nested structure that may be overlooked by standard data analysis techniques. The statistical relevance of identified clusters can be gauged using a density based validation index. [Preview Abstract] |
|
G1.00183: The effect of oxidation on charge carrier motion in PbS quantum dot thin films studied with Kelvin Probe Microscopy Lan Phuong Nguyen Hoang, Pheona Williams, Jason Moscatello, Katherine E. Aidala We developed a technique that uses scanning probe microscopy (SPM) to study the real-time injection and extraction of charge carriers in thin film devices. We investigate the effects of oxidation on thin films of Lead Sulfide (PbS) quantum dots with tetrabutyl-ammonium-iodide (TBAI) ligands in an inverted field effect transistor geometry with gold electrodes. By positioning the SPM tip at an individual location and using Kelvin Probe Force Microscopy (KPFM) to measure the potential over time, we can record how the charge carriers respond to changing the backgate voltage with grounded source and drain electrodes. We see relatively fast screening for negative backgate voltages because holes are quickly injected into the PbS film. The screening is slower for positive gate voltages, because some of these holes are trapped and therefore less mobile. We probe these trapped holes by applying different gate voltages and recording the change in potential at the surface. There are mixed reports about the effect of air exposure on thin films of PbS quantum dots, with initial exposure appearing to be beneficial to device characteristics. We study the change in current, mobility, and charge injection and extraction as measured by KPFM over hours and days of exposure to air. [Preview Abstract] |
|
G1.00184: Electron Transport through Polyene Junctions in between Carbon Nanotubes: an Ab Initio Realization Yiing-Rei Chen, Kai-Yu Chen, Kun-Peng Dou, Jung-Shen Tai, Hsin-Han Lee, Chao-Cheng Kaun With both {\it ab initio} and tight-binding model calculations, we study a system of polyene bridged armchair carbon nanotube electrodes, considering one-polyene and two-polyene cases, to address aspects of quantum transport through junctions with multiple conjugated molecules. The {\it ab initio} results of the two-polyene cases not only show the interference effect in transmission, but also the sensitive dependence of such effect on the combination of relative contact sites, which agrees nicely with the tight-binding model. Moreover, we show that the discrepancy mainly brought by {\it ab initio} relaxation provides an insight into the influence upon transmission spectra, from the junction's geometry, bonding and effective potential. [Preview Abstract] |
|
G1.00185: Band alignment study on Al/SiO$_{\mathrm{2~}}$and Cu/SiO$_{\mathrm{2\thinspace }}$metal-oxide interface with the presence of point defect Jianqiu Huang, Eric Tea, Celine Hin Metal-Oxide interface has a wide use in electronic devices. Currently, technological development is aiming on the shrinkage of electronic devices' size. Based on the knowledge of electron tunneling effect, the reduction of dielectric thickness would cause an exponential increase on electron tunneling probability which contributes to current leakage. It might cause dielectric breakdown, which could make a severe and irreversible damage to the devices. Therefore, the main purpose of this study is to explore the possible factors that can lead to dielectric breakdown at metal-oxide interface. Density functional theory \textit{ab initio} calculation has been applied to study the Al/SiO$_{\mathrm{2~}}$and Cu/SiO$_{\mathrm{2\thinspace }}$metal-oxide interface. Results on oxygen (di)vacancies at the interface will be presented and compared with the defect free model. The band alignment has been constructed to describe the variation of potential barrier height due to defect at interface. Results show the oxygen (di)vacancies at interface might trap electron and reduce potential barrier height. Moreover, the potential barrier height has a significant dependence on defects charge states. [Preview Abstract] |
|
G1.00186: Band alignment study on Al/SiO$_{\mathrm{2~}}$and Cu/SiO$_{\mathrm{2\thinspace }}$metal-oxide interface with the presence of H atom impurity and external electric field Jianqiu Huang, Eric Tea, Celine Hin Metal-Oxide interface has a wide use in electronic devices. Currently, technological development is aiming on the shrinkage of electronic devices' size. Based on the knowledge of electron tunneling effect, the reduction of dielectric thickness would cause an exponential increase on electron tunneling probability, which contributes to current leakage. It might cause dielectric breakdown, which could make a severe and irreversible damage to the devices. Therefore, the main purpose of this study is to explore the possible factors that could lead to dielectric breakdown at metal-oxide interface. Density functional theory \textit{ab initio} calculation has been applied to study the Al/SiO$_{\mathrm{2~}}$and Cu/SiO$_{\mathrm{2\thinspace }}$metal-oxide interface. Previous study revealed the facts that oxygen (di)vacancies at interface might trap electron and vary potential barrier height. In this study, we introduced the H atom impurity at interface, and applied external electric field to the system. Charge density differences have been calculated to observe the charge alternation at the interface when impurity and external electric field existed. Band alignment revealed the potential barrier height variation due to the impurity and external electric field, which provided us how barrier height would respond to these two types of defects. [Preview Abstract] |
|
G1.00187: Single crystal complex oxide on flexible substrate. Saidur Bakaul, Claudy Serrao, Oukjae Lee, Sayeef Salahuddin Flexible ferroelectrics are needed for various applications such as biocompatible energy harvesting and flexible memory. In this sector, most of the current research is focused on organic piezoelectric materials which have advantage of flexibility but suffers severely from poor energy conversion and generation efficiency. On the contrary, owing to very high electromechanical coupling factor (representing energy conversion efficiency) complex oxides are the best choices as energy harvesting and transduction elements, especially for transforming mechanical energies into electronic energy. Still their usage in energy harvesting is very limited mainly due to the stringent growth conditions of single crystals, high temperature needed for crystallization and lack of flexibility and stretchability. We have shown that single crystal Pb$_{\mathrm{0.8}}$Zr$_{\mathrm{0.2}}$TiO$_{\mathrm{3}}$ can be epitaxially transferred on flexible plastic substrate. The transferred PZT shows 70 uC/cm$^{\mathrm{2}}$ remnant polarization and dielectric constant over 100 even when it is bent. These results suggest the possibility of single crystal complex oxide devices on flexible platform. [Preview Abstract] |
|
G1.00188: Charge reorganization in LaMnO3/LaNiO3 superlattice interfaces federico iori, Alexandre Gloter Functional properties of oxide heterostructurecan recently be controlled and tuned through the electronic and structural mismatch at the interface. Artificial superlattices thin film can thus present complex magnetic structure at the interface different from their corresponding bulk building blocks. In this scenario when an antiferromagnetic buk LMO and the paramagnetic bulk LNO are combined in thin filmssuperlattices, LaMnO3/LaNiO3, strong exchange bias, new metal-insulator transition or antiferromagnetic order at the interface appear. In this work we study by ab initio Density Functional Theory how the induced magnetic moments in LNO films in LMO/LMO (111)-oriented can lead to charge transfer and reorganization at the interface among the Ni and Mn metal ions for different periodicities of the superlattices (3/3, 5/5, 7/7) and how it is possible to control them through atomic intermixing at the interface. [Preview Abstract] |
|
G1.00189: Engineering SrTiO3/LaAlO3 heterostructures thicknessthrough a metallic capping layer electrodes Federico Iori The possibility to achieve conducting and superconducting properties at the interface between two bulk insulator oxides as SrTiO3 (STO) and LaAlO3 (LAO) in 2004 [1] has wide opened the route toward the discovery and control of broad functional emerging properties in different oxides heterostructures. Nonetheless the STO/LAO system still present not clarified questions concerning the possibility to control the presence of the 2DEG at the interface. In this work we present our theoretical results supported by experimental measurementsconcerning the possibility to tune the critical thickness of the LAO topmost layer through the deposition of a metallic capping layer at the surface. Our ab initio Density Functional Theory calculations show how different metallic contact can lead to a reduction of the LAO critical thickness of 4 u.c. still preserving the 2D electronic gas at the interface. [1] Otomo and Hwang, Nature 427, 423 (2004) [Preview Abstract] |
|
G1.00190: \textbf{Growth and Study of Cuprate Thin Film Heterostructures Combining La}$_{\mathrm{\mathbf{2}}}$\textbf{CuO}$_{\mathrm{\mathbf{4+\delta ~}}}$\textbf{and LaCuO}$_{\mathrm{\mathbf{3-\delta }}}$ Rodrigo Marmol, Franklin Burquest, Nicholas Cox, Brittany Nelson-Cheeseman Cuprate materials have shown promise as fuel cell cathode materials. Both the layered perovskite, La$_{\mathrm{2}}$CuO$_{\mathrm{4+\delta }}$, and its 3D perovskite counterpart, LaCuO$_{\mathrm{3-\delta }}$, demonstrate the simultaneous electronic and ionic conduction necessary for fuel cell cathode materials. The layered perovskite allows for oxygen interstitial diffusion through the material. Meanwhile, the 3D perovskite readily creates oxygen vacancies, allowing for oxygen vacancy diffusion through the material. In this work, we investigate thin film heterostructures created from these two disparate materials to understand how the local oxygen diffusion phenomena affect the local structure and electrical transport of cuprates. The growth of these heterostructures is possible through the atomic monolayer control of Molecular Beam Epitaxy with in-situ monitoring via Reflective High Energy Electron Diffraction. The superlattice structure is characterized by x-ray reflectivity, and the crystal structure of the disparate phases is characterized by x-ray diffraction. A custom electrical transport system is used to characterize the electrical transport of the films. We compare these heterostructures with the single-phase films of La$_{\mathrm{2}}$CuO$_{\mathrm{4+\delta ~}}$and LaCuO$_{\mathrm{3-\delta ~}}$in order to understand how this heterostructuring may modify the structure and electrical properties. [Preview Abstract] |
|
G1.00191: Thermoelectric Properties of Barium Plumbate Doped by Alkaline Earth Oxides Andreza Eufrasio, Rudra Bhatta, Ian Pegg, Biprodas Dutta Ceramic oxides are now being considered as a new class of thermoelectric materials because of their high stability at elevated temperatures. Such materials are especially suitable for use as prospective thermoelectric power generators because high temperatures are encountered in such operations. The present investigation uses barium plumbate (BaPbO$_{3})$ as the starting material, the thermoelectric properties of which have been altered by judicious cation substitutions. BaPbO$_{3}$ is known to exhibit metallic properties which may turn semiconducting as a result of compositional changes without precipitating a separate phase and/or altering the basic perovskite crystal structure. Perovskite structures are noted for their large interstitial spaces which can accommodate a large variety of ``impurity'' ions. As BaPbO$_{3}$ has high electrical conductivity, $\sigma =$2.43x10$^{5}\Omega^{-1}$m$^{-1}$ at room temperature, its thermopower, $S$, is relatively low, 23$\mu $V/K, as expected. With a thermal conductivity, $k$, of 4.83Wm$^{-1}$K$^{-1}$, the figure of merit (\textit{ZT}$=S^{2}\sigma $\textit{Tk}$^{-1})$ of BaPbO$_{3}$ is only 0.01 at $T=$300K. The objective of this investigation is to study the variation of thermoelectric properties of BaPbO$_{3}$ as Ba and Pb ions are systematically substituted by alkaline earth ions. [Preview Abstract] |
|
G1.00192: The way to enhance thermoelectric properties of Bi$_{2}$O$_{2}$Q (Q$=$S and Se) system by introducing chalcogen mixture net. Changhoon Lee, Jisook Hong, Wang Ro Lee, Dae Yeon Kim, Ji Hoon Shim First principles density functional theory calculations were carried out for the series of bilayered semiconducting Bi$_{2}$O$_{2}$Q (Q$=$S, Se) and hypothetically constructed Bi2O2S0.5Se0.5 compounds in which chalogen square net of pure Bi$_{2}$O$_{2}$Q compound is replaced with having stripe type structure of chalcogen mixture net to explore their electronic structures, the change in their electronic structures under the chalcogen mixing, and the possibility for improving in their thermoelectric properties. By introducing chalcogen mixture net in pure Bi$_{2}$O$_{2}$Q, the band gap should be adjusted, and the indirect band gap in pure Bi$_{2}$O$_{2}$Q compound is changed to direct band gap. According to the analysis of calculated thermoelectric properties of Bi$_{2}$O$_{2}$Q and Bi$_{2}$O$_{2}$S$_{0.5}$Se$_{0.5}$ compounds, thermoelectric properties are strongly enhanced in Bi$_{2}$O$_{2}$S$_{0.5}$Se$_{0.5}$ compound. It seems to be due to the fact that the electrical conductivity is strongly enhanced by the decrease of dimensionality of its electronic structure and the broadening of sharpness of density of states near the Fermi level. Therefore, we believe that band modulation by introducing chalcogen mixture net in its pure compound Bi$_{2}$O$_{2}$Q compound gives a help to improve their thermoelectric properties. [Preview Abstract] |
|
G1.00193: Tunneling of Heat: Potential-Barrier Analysis. David Saroka, Kamil Walczak We examine quantum processes of heat (energy) transfer as carried by electrons tunneling via potential barriers of different shapes. As a starting point, we use analytical expressions for transmission functions related to rectangular and triangular potential barriers as well as point-like defects connecting two heat reservoirs (thermal baths). To calculate thermal conductance, we use Landauer formula for heat flux in its linear Taylor expansion with respect to temperature difference. Our results are discussed with respect to temperature, resonant states, specific parameters characterizing potential barrier (its height and width), and the effective mass of heat carriers. To get time-dependent heat fluxes reflected from and scattered on potential barriers, we use Gaussian-type wave-packet approach to tunneling of heat carried by electrons. Time-domain formulation of the scattering problem is performed by using the quantum mechanical concept of Gaussian wave packets. [Preview Abstract] |
|
G1.00194: Inelastic Heat Transfer in Molecular Quantum Dots Joanna Dyrkacz, Kamil Walczak We examine electronic heat conduction via molecular complexes in the presence of local electron-phonon coupling effects. In off-resonance transport regime, even weak electron-phonon interactions lead to phonon-mediated changes of transport characteristics. In the nearly resonance conditions, the strong electron-phonon coupling reduces the height of the main conductance peak, generating additional satellites (phonon sidebands) in transport characteristics and shifting molecular energy spectrum via reorganization (polaron) energy. In the past, it was shown that inclusion of electron-phonon coupling effects into computational scheme reduces discrepancy between theoretical results and experimental data. The aim of this project is to study electron-phonon coupling effects on electronic heat transfer at molecular level. For that purpose, we use non-perturbative computational scheme based on inelastic version of Landauer formula, where the Green's functions technique combined with polaron transformation was used to calculate multi-channel transmission probability function, while accessibility of individual conduction channels is governed by Boltzmann statistics. Our analysis is based on the hypothesis that the dynamics created by electron-phonon interaction onto the molecular quantum dot asymmetrically connected to two thermal reservoirs will lead to thermal rectification effect. Our results will be discussed in a few aspects: electron-phonon coupling strength, phonon dispersion relationship, and heat fluxes generated by temperature difference as well as bias voltage. [Preview Abstract] |
|
G1.00195: Electronic band gaps and transport properties in periodically alternating mono- and bi-layer graphene superlattices Xiong Fan, Wenjun Huang, Tianxing Ma, Li-Gang Wang, Hai-Qing Lin We investigated electronic band structure and transport properties of periodically alternating mono- and bi-layer graphene superlattices (MBLG SLs). In such MBLG SLs, there exists the zero-averaged wave vector (zero-$\overline{k}$) gap, which is insensitive to the lattice constant, and this zero-$\overline{k}$ gap can be controlled via changing both the ratio of potentials' widths and the interlayer coupling coefficient of bilayer graphene. It is also found that there exist the extra Dirac points and their conditions are analytically presented. Lastly, it shows that the electronic transport properties and the energy gap ($E_{g}$) of the first two bands in MBLG SLs are tunable by the interlayer coupling and the widths' ratio of the periodic mono- and bi-layer graphene. [Preview Abstract] |
|
G1.00196: Exact solutions for 1D lattice models with topological complicated configuration Lei Fang, David Schmeltzer In this work a transfer matrix method is developed to study 1D lattice models within the tight binding framework. Employing this method we show, from simple to difficult, the solutions of a semi-infinite wire, a finite open wire, a single closed ring and two coupled rings. We start by studying local properties of solutions in a homogeneous region. It is found that a calculation of the exponential of the transfer matrix is necessary for us to obtain the general form of wave functions in the entire homogenous region. Then by matching wave functions at boundaries or connecting junctions we can get equations that determine the spectrum. In this way we have solved the problem of two coupled rings (a topologically complicated configuration) and it is shown there can exist bound state in this system. [Preview Abstract] |
|
G1.00197: Identifying radiation induced point defect in SiC nanowires: computational modeling. Ming Uu SiC nanowires (NWs) are expected to possess higher radiation tolerance compared to their crystalline counterpart due to their efficiency in eliminating point defects generated by the radiations. In this study, we will develop a computational modeling scheme to identify the radiation induced point defects in SiC NWs. A preliminary study on the hexagonal 2H-SiC NWs has demonstrated that the point defects on the surface of the SiC NWs only create local distortions and will not cause the destruction of the entire structure of the SiC NWs. It is also found that the local strain created by the antisite, the C-vacancy, and the Si-interstitial defects induces a few impurity states inside the energy gap, while defects such as the Si-vacancy and C-interstitial defects tend to produce a small tail at the top of the valence band. These observations suggest that the electronic properties of the SiC NWs will not be affected to any great extent by these types of points defects on the surface of the SiC NWs, and therefore the SiC NWs are expected to be tolerant or resistant responding to these types of radiation effect. [Preview Abstract] |
|
G1.00198: Magnetotransport experiments in two-dimensional electron gases exposed to electromagnetic hybrid superlattices Jakob Schluck, Stefan Fasbender, Stephan Wissenberg, Thomas Heinzel, Klaus Pierz, Hans-Werner Schumacher, Dimitris Kazazis, Ulf Gennser Hybrid lateral superlattices composed of a square array of antidots and a periodic one-dimensional magnetic modulation are prepared in Ga[Al]As heterostructures. The two-dimensional electron gases exposed to these superlattices are characterized by magnetotransport experiments in various magnetic field configurations. Commensurability resonances as a function of a parallel external magnetic field are observed even in the absence of closed orbits, and interpreted with the help of numerical simulations based on the semiclassical Kubo model. [1] In additional homogeneous perpendicular magnetic fields, quantum effects emerge, which can be attributed to the formation of closed quantized orbits. \newline [1] J. Schluck et al.,Phys. Rev. B 91, 195303 (2015) [Preview Abstract] |
|
G1.00199: \textbf{Electric field dependent Electroreflectance of GaAs/AlGaAs multiple quantum well Bragg structure at second quantum state} Mim Nakarmi, Naresh Shakya, Vladimir Chaldyshev Electroreflectance Spectroscopy was employed to study the effect of electric field on the excitonic transitions in a GaAs/AlGaAs multiple quantum well (MQW) Bragg structure. The sample used in this experiment consists of 60 periods of quantum well structures with GaAs well layer (\textasciitilde 13 nm) and AlGaAs barrier layer (\textasciitilde 94 nm), grown by molecular beam expitaxy on a semi-insulating GaAs substrate. The sample structure was designed to coincide the Bragg resonance peak with the x(e2-hh2) exciton transitions. We observed a significant enhancement of excitonic feature around the x(e2-hh2) exciton transition due to the double resonance along with the sharp features of x(e1-hh1) and x(e1-lh1) ground state exciton transitions by tuning the angle of incidence of the light. We will present the results on electric field dependent electroreflectance measurements of this structure and discuss the effect of electric field on the first and second energy states. [Preview Abstract] |
(Author Not Attending)
|
G1.00200: "Flash" synthesis of "giant" Mn-doped CdS/ZnSe/ZnS nanocrystals with ZnSe layer as hole quantum-well Ruilin Xu, Jiayu Zhang Usually, exciton-Mn energy transfer in Mn-doped CdS/ZnS nanocrystals (NCs) can readily outcompete the exciton trapping by an order of magnitude. However, with the accumulation of non-radiative defects in the giant shell during the rapid growth of the thick shell (up to \textasciitilde 20 monolayers in no more than 10 minutes), the photoluminescence (PL) quantum yield of this kind of “giant” NCs is significantly reduced by the accumulation of non-radiative defects during the rapid growth of thick shell. That is because the exciton-Mn energy transfer in Mn-doped CdS/ZnS NCs is significantly inhibited by the hole trapping as the major competing process, resulting from the insufficient hole-confinement in CdS/ZnS NCs. Accordingly “flash” synthesis of giant Mn-doped CdS/ZnSe/ZnS NCs with ZnSe layer as hole quantum-well is developed to suppress the inhibition. Meanwhile Mn$^{\mathrm{2+}}$ PL peak changes profoundly from \textasciitilde 620 nm to \textasciitilde 540 nm after addition of ZnSe layer. Studies are under the way to explore the relevant mechanisms. [Preview Abstract] |
|
G1.00201: Electron spin decoherence in silicon carbide nuclear spin bath Li-Ping Yang In this paper, we study the electron spin decoherence of single defects in silicon carbide (SiC) nuclear spin bath. We find that, although the natural abundance of 29Si (~4.7%) is about 4 times larger than that of 13C (~1.1%), the electron spin coherence time of defect centers in SiC nuclear spin bath in strong magnetic field (B>300 Gauss) is longer than that of nitrogen-vacancy (NV) centers in 13C nuclear spin bath in diamond. In addition to the smaller gyromagnetic ratio of 29Si, and the larger bond length in SiC lattice, a crucial reason for this counter-intuitive result, is the suppression of heteronuclear-spin flip-flop process in finite magnetic field. Our results show that electron spin of defect centers in SiC are excellent candidates for solid state spin qubit in quantum information processing. [Preview Abstract] |
|
G1.00202: Current conserving theory at the operator level Jiangtao Yuan, Yin Wang, Jian Wang The basic assumption of quantum transport in mesoscopic systems is that the total charge inside the scattering region is zero. This means that the potential deep inside reservoirs is effectively screened and therefore the electric field at interface of scattering region is zero. Thus the current conservation condition can be satisfied automatically which is an important condition in mesoscopic transport. So far the current conserving ac theory is well developed by considering the displacement current which is due to Coulomb interaction if we just focus on the average current. However, the frequency dependent shot noise does not satisfy the conservation condition since we do not consider the current conservation at the operator level. In this work, we formulate a generalized current conserving theory at the operator level using non-equilibrium Green's function theory which could be applied to both average current and frequency dependent shot noise. A displacement operator is derived for the first time so that the frequency dependent correlation of displacement currents could be investigated. Moreover, the equilibrium shot noise is investigated and a generalized fluctuation-dissipation relationship is presented. [Preview Abstract] |
|
G1.00203: Photonic Surface-Bulk Waves in 1D All-Dielectric Metamaterials Anne DeLua, David Keene, Maxim Durach It has been previously reported that it is impossible to satisfy the strong condition for the propagation of Dyakonov Surface Waves in 1D all-dielectric metamaterials. The strong condition requires that both evanescent and ordinary waves decay into the metamaterial. We show that the weak condition, when only ordinary waves decay, can be satisfied in 1D all-dielectric metamaterials, which gives rise to a new class of photonic resonances that combine evanescent extraordinary and non-evanescent ordinary waves in one excitation. By combining thin layers of such metamaterials with different dielectric and metal substrates one can excite resonances that are a hybrid between Fabry-Perot modes in the metamaterial layer and surface waves on the boundaries of this layer. [Preview Abstract] |
|
G1.00204: Scattering on hyperbolic microspheres: From photonic nanojets to Poisson-Arago bright spots Reed Hodges, Cleon Dean, Maxim Durach We investigate optical properties of metal-dielectric metamaterial microspheres composed of subwavelength spherical shells of two different materials alternating in an onion-layer fashion. Recently such metamaterial spheres were considered as cavities and their whispering gallery modes were investigated. We focus on the scattering of external radiation by the meta-micropheres in this work. We show that different scenarios are produced by altering the metal fraction in the spheres: as the microsphere transitions from all-dielectric to hyperbolic to all-metal, the photonic nanojets transform into Poisson-Arago bright spots. A new phenomenon also emerges as the percentage of metal in the microsphere increases. ``Hot spots'' of optical fields intensity appear at the center of the sphere. Their intensity is much higher than that of the incident plane wave. [Preview Abstract] |
|
G1.00205: Image magnification in transformation optics devices based on tapered waveguides William Zimmerman, Christopher Jensen, Vera Smolyaninova, Igor Smolyaninov Recent progress in metamaterial and transformation optics (TO) research gave rise to such fascinating devices as perfect lenses, invisibility cloaks, and numerous other unusual electromagnetic devices. However, the metamaterials have problems with low-loss broadband performance and complexity of fabrication, especially in the visible frequency range. Our TO devices allow us to circumvent these difficulties by using lithographically defined metal/dielectric waveguides to emulate metamaterial properties [1]. Adiabatic variations of the waveguide shape enable control of the effective refractive index experienced by light propagating inside the waveguide. The achieved image magnification is consistent with numerical simulations. We have studied wavelength and polarization dependent performance of the waveguides. Our experimental designs appear to be broadband, which has been verified in the 480-633 nm range. These novel optical devices considerably extend our ability to control light on sub-micrometer scales. [1]. V.N. Smolyaninova, et al., Phys. Rev. B 87, 075406 (2013) [Preview Abstract] |
|
G1.00206: OPTICAL SPECTRA OF A MULTILAYER STACK COMPOSED OF HIGH-TEMPERATURE SUPERCONDUCTOR AND DIELECTRIC Silvia Cortes-Lopez, Felipe Perez-Rodriguez Layered high-temperature superconductors behave as negative-refractive-index hyperbolic metamaterials, having effective permittivity components, parallel and perpendicular to the superconducting planes, with different infrared Josephson plasma frequencies [1]. Here, we theoretically study the reflectivity and transmissivity of a multilayer stack with alternating high-temperature superconductor and dielectric slabs. For TM electromagnetic waves, it was found that both reflectivity and transmissivity exhibit narrow photonic pass bands corresponding to two types of Fabry-Perot resonances, one occurring in the superconductor, whereas the other in the dielectric slab. For a stack of N unit cells, in each narrow photonic pass band there are N-1 transmissivity peaks, associated to the quantization of the Bloch phase within the stack. In contrast, when both types of Fabry-Perot resonances are close to each other, the infrared pass bands become wide and the N-1 strong peaks in the optical spectra are clearly-separated. In addition, new resonances are observed at the top and the bottom of the pass bands, and a photonic band just below the lower Josephson plasma frequency appears. \\ [1] A.L. Rakhmanov, et al, Phys. Rev. B {\bf 81}, 075101 (2010). [Preview Abstract] |
|
G1.00207: Microwave propagation in chiral metamaterials Aida Prybylski, Luis Yon, Natalia Noginova Chiral hyperbolic metamaterials are predicted to show interesting properties associated with possible topological photonic states in these materials, which present new opportunities for light control and manipulation. As prototypes, we consider two metal-dielectric systems designed for microwave range: a twisted wires array, where chirality is associated with shape of metal inclusions, and a rotated layer system, with parallel wires in each layer, and direction of the wires orientation rotated from layer to layer. Systems with different content of metal and layer-to-layer distance were fabricated and studied in the free space propagation experiment. The results were discussed in terms of effective media consideration. [Preview Abstract] |
|
G1.00208: Temperature-dependent thermal transport in holey silicon nanostructures investigated by impulsive stimulated thermal scattering Ryan Duncan, Alejandro Vega-Flick, Alexei Maznev, Zhengmao Lu, Lingping Zeng, Jiawei Zhou, Jean-Philippe Peraud, Evelyn Wang, Gang Chen, Keith Nelson Nanostructuring of semiconductor materials provides a promising means for the decoupling of their electronic and thermal conductivities, making such systems of great interest to the fields of thermoelectrics and microelectronics. Prior investigations indicated that Brillouin zone-folding and phononic band-gap formation may play a role in the diminished thermal conductivity observed in such structures, although it is unclear to what degree such effects manifest themselves over different temperature ranges. We investigate thermal transport properties as a function of temperature for a series of nanoporous silicon membranes using impulsive stimulated thermal scattering (ISTS)---a non-contact optical technique for measuring in-plane thermal transport. Measurements were carried out at temperatures ranging from 350 to 84 K on samples with pore diameters of 130 nm and pitch sizes ranging from 150 to 500 nm. Monte Carlo simulations for phonon transport were performed for comparison to experimental observations. We will discuss the experimental and computational results, and attempt to determine whether the experimental data are consistent with the diffuse boundary scattering model in which phononic crystal effects are absent. [Preview Abstract] |
|
G1.00209: Counterintuitive behavior of simulated network's conductance analogous to the Braess paradox S\'ebastien Toussaint, Demetrio Logoteta, Marco Pala, Vincent Bayot, Benoit Hackens Suppressing a channel from a two-terminal mesoscopic network defined in a two-dimensional electron system (2DES) can paradoxically increase its conductance. This counterintuitive behavior analogous to the Braess paradox is evidenced in [1] by simulating the network’s conductance (G) when progressively depleting one of its channels with a biased local probe. By means of 3D self-consistent Poisson-Schr\"odinger simulations based on the NEGF formalism we investigate the occurrence circumstances of this transport anomaly under the influence of a scanning tip. By simulating the current density and local density of states within the network in the coherent and ballistic transport regime, we can follow the modification of the electron flow when the anomaly occurs. This allows to get insights about the role of a simulated disordered potential within the 2DES and permit to evaluate the tip influence on the 2DES potential landscape. Interference phenomena between different network paths can be modified by simulating G under a magnetic field orthogonal to the 2DES. Different geometries and network congestion are also discussed. [1] M. G. Pala \textit{et al}., Phys. Rev. Lett. 108, 076802 (2012). [Preview Abstract] |
|
G1.00210: SURFACES, INTERFACES AND THIN FILMS |
|
G1.00211: Evolution of the Adsorption Phases on (111) Terraces With Their Width Alain Phares, David Grumbine We study the evolution of the crystallization patterns, or phases, of monomer adsorption on (111) terraces, with the number $M$ of atomic sites in the width of the terrace up to and including $M = 8$. Pairwise adsorbate-adsorbate first, second and third neighbor interactions, whether attractive or repulsive, are taken into account. [Preview Abstract] |
|
G1.00212: Studies of Surface morphology and Atomic Force Microscope-induced Surface Modifications in Calcium Manganese Oxide (CaMnO) Thin Films Anthony Johnson, Cacie Hart, Adeel Chaudhry, Bridget Lawson, Natalie Ferrone, Samuel Neubauer, David Houston, Rajeswari Kolagani, David Schaefer CaMnOis a material of interest for applications as a catalyst for renewable energy applications. Our recent work on epitaxial thin films of this material has shown that films with a tensile lattice mismatch strain exhibit structural and electrical properties that indicate oxygen deficiency. We are studying the influence of strain and oxygen stoichiometry variations on surface morphology as revealed by atomic force microscopy. Our previous work in epitaxial thin films of the hole doped manganite nanoscale has demonstrated surface modifications induced by a voltage-biased AFM tip. Such surface modifications have been shown to be associated with changes in cation and oxygen stoichiometry. We will report results of similar studies on strained CaMnOthin films; relevant for understanding the surface mobility of oxygen vacancies. [Preview Abstract] |
|
G1.00213: Glow-Discharge Production of Oxygen from the Martian Atmosphere Caleb Hughes, Ronald Outlaw One of the most crucial aspects of any mission to Mars is a continual supply of oxygen for astronaut respiration on site. The most popular approach to this problem favors in-situ oxygen production on Mars, utilizing the \textit{CO}$_{2}$ Martian atmosphere. However, this requires a large energy budget. NASA's current plans for Mars include sending a system called MOXIE, which produces oxygen through solid oxide electrolysis at high temperatures. An alternative approach utilizes the 6 Torr Martian atmosphere to provide a continual source of oxygen by breaking down the molecule into \textit{CO} and $O$ using a glow-discharge. After dissociation, a thin film \textit{Ag }membrane uniquely permeates the atomic oxygen which then recombines to $O_{2\thinspace } $on the downstream side, where it is subsequently stored. By taking advantage of recent advances in thin film technology to reduce the thickness of the film to many orders of magnitude less than used in the initial study, a corresponding increase in $O_{2}$ flux can be realized. The \textit{Ag} thin film requires the support of a porous ceramic substructure. With this system, it is shown that this method produces a viable energy efficient alternative to MOXIE. [Preview Abstract] |
|
G1.00214: Electronic Phase Exhibits Attraction Between Like Net Charges Thomas Manz A new electronic phase transition was observed in thin plastic films metallized with gold, optionally with an additional layer of aluminum metallization. This phase transition occurred only when the dielectric layers of two metallized films faced each other. When charged to high voltage magnitudes and then grounded, an electronic phase transition occurred during the discharge step that led to a strong attraction between the paired metallized films, even though the films carried like net charges. The resulting electronic phase (and its attractive force) persisted for several days with no apparent decay at ambient temperatures (c. 25 C). After rotating the films along an axis not parallel to the films, the magnetic field due to rotational motion of the charge carriers relative to the thin films persisted for seconds before dissipation. This demonstrates free current lifetimes lasting seconds. Computations and experiments were performed that show the underlying mechanism for the attraction of like net charges is scattering of electromagnetic waves by an electric field cusp at the charged interfaces. Scattering theory calculations reveal this scattering should be most prevalent in the infrared and microwave regions. This has potential applications for shielding electronic circuits from electromagnetic noise at these wavelengths. [Preview Abstract] |
|
G1.00215: Resistivity Effects of Cation Ordering in Highly-Doped La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4}}^{\mathrm{\thinspace }}$Epitaxial Thin Films Franklin Burquest, Rodrigo Marmol, Nicholas Cox, Brittany Nelson-Cheeseman Highly-doped La$_{\mathrm{2-x}}$Sr$_{\mathrm{x}}$CuO$_{\mathrm{4}}$ (LSCO) films (0.5 $\le $ x $\le $ 1.0) are promising for many applications due to their electronic, ionic, and phonon transport. In this study, we investigate the effect of ``electrostatic strain'' on the electrical transport of LSCO thin films with large doping (x$=$0.5, 0.75, and 1.0). This ``electrostatic strain'' is applied by ordering differently charged A-site cations (La$^{\mathrm{3+}}$ vs. Sr$^{\mathrm{2+}})$ into charged A-O layers within the crystal structure. This causes internal polar electrostatic forces, which have been shown to cause stretching of the apical oxygen bond in analogous epitaxial nickelate films. Thin film samples are grown concurrently to minimize extraneous effects on film structure and properties. Atomic force microscopy and x-ray reflectivity demonstrate that the films are single crystalline, epitaxial, and smooth. X-ray diffraction is used to measure the c-axis of the films as a function of doping and dopant cation ordering. Electrical transport data of the ordered samples is compared with transport data of conventional disordered cation samples. Preliminary data indicates significant differences in resistivity at both 300K and 10K between the cation-ordered and cation-disordered samples. This work indicates that dopant cation ordering within the layered cuprates could significantly modify the conduction mechanisms at play in these materials. [Preview Abstract] |
|
G1.00216: Effects of Cd Interlayer on CdS/CdTe Thin Film Photovoltaics David Rivella, Luis Cerqueira, M. Alper Sahiner CdS/CdTe thin films are well known for their photovoltaic effects. However, it is also known that there are various factors that limit the output of the photovoltaic cells. In these particular thin films, a limiting factor is the interaction of CdS and the CdTe layers. By adding a Cd layer between CdS and CdTe, a buffer zone was created. Therefore, the interaction between the aforementioned layers was changed. In this study, the buffer zone was added to the photovoltaic cells, while the ratio of Cd to Te in the CdTe layer was varied, in order to observe the effects of the buffer in regards to the diffusion of Te in traditional CdTe/CdS photovoltaics. The samples were created on ITO coated glass using pulsed laser deposition. This created uniform samples with an approximate thickness of 0.75 microns. In order to test the effect of the Cd buffer layer, the CdTe layers were deposited with varying ratios of Cd to Te. XRD analysis confirmed that the deposited Cd and Te formed crystalline CdTe. The active carrier concentrations were then determined using Hall Effect measurements. The photovoltaic properties were measured using Keithley source meter set-up. The effect of structural modifications on the active carrier concentrations and photovoltaic properties will be discussed. [Preview Abstract] |
(Author Not Attending)
|
G1.00217: Exploration of Al-Doped ZnO in Photovoltaic Thin Films Christopher Ciccarino, M. Alper Sahiner The electrical properties of Al doped ZnO-based thin films represent a potential advancement in the push for increasing solar cell efficiency. Doping with Aluminum will theoretically decrease resistivity of the film and therefore achieve this potential as a viable option in the P-N junction phase of photovoltaic cells. The n-type semi-conductive characteristics of the ZnO layer will theoretically be optimized with the addition of Aluminum carriers. In this study, Aluminum doping concentrations ranging from 1-3{\%} by mass were produced, analyzed, and compared. Films were developed onto ITO coated glass using the Pulsed Laser Deposition technique. Target thickness was 250 nm and ellipsometry measurements showed uniformity and accuracy in this regard. Active dopant concentrations were determined using Hall Effect measurements. Efficiency measurements showed possible applications of this doped compound, with upwards of 7{\%} efficiency measured, using a Keithley 2602 SourceMeter set-up. XRD scans showed highly crystalline structures, with effective Al intertwining of the hexagonal wurtzile ZnO molecular structure. This alone indicates a promising future of collaboration between these two materials. [Preview Abstract] |
|
G1.00218: Electrical Properties Analysis of Copper doped CdTe/CdS Deposited Thin Films on ITO Coated Glass Substrates Darren Lesinski, James Flaherty, M. Alper Sahiner CdTe proves to be a viable source for renewable energy in the form of photovoltaic conversion. While CdTe/CdS naturally provide interesting results adding dopants to the cell can yield higher conversion efficiencies. Copper, famous for its electrical properties, can be used as a dopant in the CdTe layer. In conjunction with its dopant characteristics Copper also improves cell performance by acting as a low resistant and high current back contact. All thin films were synthesized using pulsed laser deposition onto ITO coated glass substrates. The CdS layer across all cells has an approximate thickness of 1500 Angstroms. The following CdTe layer has an approximate thickness of 5500 Angstroms. This created the base cell that was then doped. Cu, typically deposited using sublimation or vapor deposition, was done by PLD as well. Two of the three base cells were treated with Cu using the same deposition parameters. The third cell also received a CdCl treatment on top of the Cu layer to understand the effect when the oxygen layer is deferred. Ellipsometer measurements were used to confirm layer thickness. XRD analysis was used to confirm the presence of Cu and the crystal structure of the thin films. A Hall Effect Measurement system was used to measure active charge carrier concentration introduced by dopant. Also, a Keithley sourcemeter was utilized to determine photovoltaic properties. Notable results discussed will be the effects of Copper dopant on the electrical properties of CdS/CdTe based solar cells. [Preview Abstract] |
|
G1.00219: Synthesis and Characterization of Varying Concentrations of Ag-doped ZnO Thin Films Justin Hachlica, Patrick Wadie-Ibrahim, M. Alper Sahiner Silver doped ZnO is a promising compound for photovoltaic solar cell use. Doping this compound with varying amounts of silver will theoretically make this type of thin film more efficient by reducing the overall resistance and increasing the voltage and current output. The extent of this promise is being tested experimentally, by analysis of both the electrical and the surface roughness properties of the cells. Ag-doped Zinc Oxide is deposited by method of Pulsed Laser Deposition (PLD) onto Indium Tin Oxide (ITO) coated Glass. Annealing effects were also observed by varying the temperature at which the annealing occurred after synthesis of the sample. Thickness is confirmed by use of Ellipsometery. X-Ray Diffraction (XRD) measurements confirmed a ZnO crystal structure on the thin films. The active dopant carrier concentrations were determined using a Hall Effect Measuring System. Finally, the photovoltaic properties of the film are recorded by using a Keithley Source Meter. The structural characterization and electrical results of the effect of Ag doping on ZnO will then be discussed. [Preview Abstract] |
|
G1.00220: Tetrahedral cluster and pseudo molecule: New approaches to Calculate Absolute Surface Energy of Zinc Blende (111)/(-1-1-1) Surface Yiou Zhang, Jingzhao Zhang, Kinfai Tse, Lun Wong, Chunkai Chan, Bei Deng, Junyi Zhu Determining accurate absolute surface energies for polar surfaces of semiconductors has been a great challenge in decades. Here, we propose pseudo-hydrogen passivation to calculate them, using density functional theory approaches. By calculating the energy contribution from pseudo-hydrogen using either a pseudo molecule method or a tetrahedral cluster method, we obtained (111)/(-1-1-1) surfaces energies of Si, GaP, GaAs, and ZnS with high self-consistency. Our findings may greatly enhance the basic understandings of different surfaces and lead to novel strategies in the crystal growth. [Preview Abstract] |
|
G1.00221: Surface studies of gallium nitride quantum dots grown using droplet epitaxy on bulk, native substrates Christina Jones, Sunyeol Jeon, Rachel Goldman, Yizhak Yacoby, Roy Clarke Gallium nitride (GaN) and its applications in light-emitting diodes play an integral part in efficient, solid-state lighting, as evidenced by its recognition in the 2014 Nobel prize in physics. In order to push this technology towards higher efficiency and reliability and lower cost, we must understand device growth on bulk GaN substrates, which have lower defect densities and strain than template GaN substrates grown on sapphire. In this work, we present our findings on the surface properties of GaN quantum dots (QDs) grown on commercial bulk GaN. QDs are grown using the droplet epitaxy method and analyzed using a surface X-ray diffraction technique called Coherent Bragg Rod Analysis (COBRA), which uses phase retrieval to reconstruct atomic positions near the substrate surface. While several QD growth conditions in our study produce dense QDs, COBRA reveals that only low nitridation temperatures result in GaN QDs that are coherent with the bulk GaN substrate. Results are supported with atomic force microscopy and high-resolution transmission electron microscopy. [Preview Abstract] |
|
G1.00222: Noncontact Atomic Force Microscopy Study of Surface Structural Transitions and Charge Distribution Modulations on SrTiO$_{\mathrm{3}}$(100) Omur Dagdeviren, Georg Simon, Ke Zou, Charles Ahn, Fred Walker, Eric Altman, Udo Schwarz The surface structures of SrTiO$_{\mathrm{3\thinspace }}$(100) single crystals were examined as a function of annealing time and temperature in either oxygen or ultra-high vacuum (UHV) using noncontact atomic force microscopy (NC-AFM), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). Samples were subsequently analyzed for the effect the modulation of their charge distribution had on their surface potential. It was found that the evolution of the$_{\mathrm{\thinspace }}$surface roughness, termination, and reconstruction depends crucially on the preparation scheme. For example, transitions from (1x1) termination to an intermediate c(4x2) reconstruction to ultimately a (sqrt(13) x sqrt(13))-$R$33.7\textdegree surface were observed for annealing in oxygen. In UHV, the inverse transition occurred and was accompanied by an increase in surface Sr while the surface oxygen content decreased. Complementary NC-AFM measurements showed a non-monotonic trend for surface roughness with annealing temperature, which is explained by electrostatic modulations of the surface potential caused by increasing oxygen depletion. This is further corroborated by experiments in which the apparent roughness tracked in NC-AFM could be correlated with changes in the surface charge distribution. [Preview Abstract] |
|
G1.00223: Diffusion of Copper through Ti overlayer Britt Long, A. Menchaca, A. R. Chourasia The Cu/Ti interface has been characterized by x-ray photoelectron spectroscopy and resistivity measurements. Thin films of titanium were deposited on copper substrates by e-beam method. The thickness of the Ti film was kept at 50 {\AA}. The interface was annealed at temperatures of 100, 200, 300 and 400\textdegree C. The Ti 2p and Cu 2p regions were analyzed by XPS. The diffusivity of copper through titanium has been investigated. The resistivity measurements were done by the four probe method. The correlation between the resistivity and the surface composition has been evaluated. [Preview Abstract] |
|
G1.00224: Fabrication and structural characterization of highly ordered titania nanotube arrays Hongtao Shi, Rosita Ordonez Titanium (Ti) dioxide nanotubes have drawn much attention in the past decade due to the fact that titania is an extremely versatile material with a variety of technological applications. Anodizing Ti in different electrolytes has proved to be quite successful so far in creating the nanotubes, however, their degree of order is still not nearly as good as nanoporous anodic alumina. In this work, we first deposit a thin layer of aluminum (Al) onto electropolished Ti substrates, using thermal evaporation. Such an Al layer is then anodized in 0.3 M oxalic acid, forming an ordered nanoporous alumina mask on top of Ti. Afterwards, the anodization of Ti is accomplished at 20 V in solutions containing 1 M NaH$_{2}$PO$_{4}$ and 0.5{\%} HF or H$_{2}$SO$_{4}$, which results in the creation of ordered titania nanotube arrays. The inner pore diameter of the nanotubes can be tuned from \textasciitilde 50 nm to \textasciitilde 75 nm, depending on the anodization voltage applied to Al or Ti. X-ray diffractometry shows the as-grown titania nanotubes are amorphous. Samples annealed at different temperatures in ambient atmosphere will be also reported. [Preview Abstract] |
|
G1.00225: High-Performance Simulations of the Diffusion Characteristics of a Pentacene Derivative on Gold Surfaces Ryan Miller, Amanda Larson, Karsten Pohl Pentacene serves as a backbone for several molecules that provide attractive qualities for organic photovoltaic devices. One of these pentacene derivatives is 5 6,7-trithiapentacene-13-one (TTPO), which is unique in that it achieves its lowest energy configuration on Au(1 1 1) surfaces with the thiol group angled down towards the surface, allowing many molecules to pack closely together and form molecular nanowires. However, TTPO diffuses on flat surfaces, making it difficult for the self-assembly process to be initiated. With the help of the low-energy sites in surface defects and Au(7 8 8) step edges, TTPO molecules can be anchored in place on surfaces, allowing for chain formation to begin. By using high-performance Density Functional Theory based molecular dynamics calculations, the molecules can be shown to stay localized to these bonding sites and serve as a basis for chain formation. In addition, by simulating various temperatures with a Nose-Hoover thermostat, we can analyze how temperature affects anchoring ability and diffusion properties. [Preview Abstract] |
|
G1.00226: ABSTRACT WITHDRAWN |
|
G1.00227: XPS and AFM Investigation of Ti-CuO Interface Darius Durant, Ritesh Bhakta, A. R. Chourasia The techniques of x-ray photoelectron spectroscopy and atomic force microscopy have been employed to study the Ti/CuO interface. Thin films of titanium were deposited on CuO at room temperature by e-beam method. The thickness of the titanium film was varied between 3 {\AA} and 10 {\AA}. The titanium 2p, oxygen 1s and copper 2p regions were investigated by XPS. The spectral data show the reduction of CuO to elemental copper. Titanium is observed to get oxidized to TiO$_{\mathrm{2}}$. The thickness of TiO$_{\mathrm{2}}$ depended upon the initial thickness of the titanium overlayer. The reaction is observed to continue until the titanium overlayer is 7 {\AA} thick. Beyond this thickness unreacted titanium is observed. The AFM study shows nonuniformity of the TiO$_{\mathrm{2}}$ film on copper. The study provides a means of preparing TiO$_{\mathrm{2}}$ of nano-dimensions. [Preview Abstract] |
|
G1.00228: Neutron scattering study of the freezing of water near a cupric oxide surface J. Torres, Z. N. Buck, F. Z. Zhang, T. Chen, R. A. Winholtz, H. Kaiser, H. B. Ma, H. Taub, M. Tyagi Oscillating heat pipes (OHP) offer promising two-phase heat transfer for a variety of applications, including cooling of electronic devices.$^{\mathrm{2}}$ Recently, it has been shown that a hydrophilic CuO coating on either the evaporator or condenser sections of a flat-plate OHP can significantly enhance its thermal performance.$^{\mathrm{3}}$ This finding has motivated us to assess the strength of the CuO/H$_{\mathrm{2}}$O interaction by investigating the freezing behavior of H$_{\mathrm{2}}$O in proximity to a CuO surface. Using the High-Flux Backscattering Spectrometer at NIST, we have measured the intensity of neutrons scattered elastically from a well-hydrated sample of CuO-coated Cu foils that mimic the oxide surfaces in a flat-plate OHP. We observe abrupt freezing of bulk-like H$_{\mathrm{2}}$O above the CuO surface at 270 K followed by continuous freezing of the interfacial H$_{\mathrm{2}}$O down to 265 K. This freezing behavior is qualitatively similar to that found for water near a zwitterionic single-supported bilayer lipid membrane.$^{\mathrm{3}}$ Further studies are planned to compare the diffusion coefficients of the interfacial water for the coated and uncoated OHPs.$^{\mathrm{2}}$ $^{\mathrm{2}}$F. Z. Zhang \textit{et al}., submitted to J. Heat Transfer. $^{\mathrm{3}}$M. Bai \textit{et al}., Europhys. Lett. \textbf{98}, 48006 (2012); Miskowiec \textit{et al}., Europhys. Lett. \textbf{107}, 28008 (2014). [Preview Abstract] |
|
G1.00229: The effect of ultraviolet irradiation on data retention characteristics of resistive random access memory. Kentaro Kinoshita, Kouhei Kimura, Koutoku Ohmi, Satoru Kishida It is getting more and more serious to generate soft-errors by cosmic radiation, with increasing the density of memory devices. Therefore, the irradiation resistance of resistance random access memory (ReRAM) to cosmic radiation has to be elucidated for practical use. In this paper, we investigated the data retention characteristics against ultraviolet irradiation to ReRAM with Pt/NiO/ITO structure. Soft-errors were confirmed to be caused by ultraviolet irradiation in both low and high resistance states. The analysis of irradiation frequency dependence of data retention characteristics suggested that electronic excitation by the irradiation caused the errors. Based on a statistically estimated soft-error rate, the errors were suggested to be caused by aggregation and dispersion of oxygen vacancies due to the generation of electron-hole pairs and valence change by the ultraviolet irradiation. [Preview Abstract] |
|
G1.00230: Effects of Post-Deposition Annealing on the Properties of Calcium Manganese Oxide Thin Films Natalie Ferrone, Adeel Chaudhry, Cacie Hart, Bridget Lawson, David Houston, Samuel Neubauer, Anthony Johnson, David Schaefer, Rajeswari Kolagani We will present our results on the effects of post-deposition annealing on the structural and electrical properties of CaMnO$_{3-d}$ thin films grown by Pulsed Laser deposition. The thin films are epitaxially grown on (100) LaAlO$_{3}$ which has larger in-plane lattice parameters than that of bulk CaMnO$_{3}$, which leads to bi-axial tensile strain in the thin films. Results from our laboratory show that bi-axial tensile strain leads to low resistivity in thinner films, the resistivity increasing with increasing thickness. These results are suggestive of a coupling between strain and oxygen stoichiometry in the thin films. We have investigated the effects of post-deposition annealing in various gas ambients towards the goal of understanding the effects of relaxation and oxygen stoichiometric changes. We will present a comparison of the structural and electrical properties of as-grown and post-annealed films over a range of thicknesses. [Preview Abstract] |
|
G1.00231: ATOMIC, MOLECULAR AND OPTICAL (AMO) PHYSICS |
|
G1.00232: Second quantization of propagation of light through Rb vapor Zhihao Xiao, Robert Lanning, Mi Zhang, Irina Novikova, Eugeniy Mikhailov, Jonathan Dowling We model the propagation of squeezed light, in Laguerre-Gaussian spatial modes, through a non-linear medium such as Rb vapor. We examine the changes in both quantum state and spatial modes. We simulate the injection into a Rb vapor cell a linearly polarized laser beam to create squeezed vacuum state of light linearly polarized in the perpendicular direction. We fully quantize the optical field's propagation which is originally based on semi-classical calculation. The Rb atomic structure is simplified to a three-level system. We reveal the mechanism that how squeezed state of light is generated in this process and compare the theory with our experiment. We further investigate the impact on squeezing due to the change of parameters and produce schemes which improve the squeezing in the desired spatial modes. [Preview Abstract] |
|
G1.00233: Modelling Spatial Modes of Squeezed Vacuum R. Nicholas Lanning, Zhihao Xiao, Mi Zhang, Irina Novikova, Eugeniy E. Mikhailov, Jonathan P. Dowling We develop a fully quantum model to describe the spatial mode properties of squeezed light generated as a strong laser beam propagates through a Rb vapor cell. Our results show that a Gaussian pump beam can generate a collection of higher order Laguerre-Gaussian squeezed vacuum modes, each carrying a particular squeeze parameter and squeeze angle. We show that a proper sorting of modes could lead to improved noise suppression and thus make this method of squeezed light generation very useful for precision metrology. [Preview Abstract] |
|
G1.00234: Ground state configurations in two-mode quantum Rabi models Suren Chilingaryan, B. M. Rodr\'{\i}guez-Lara We study two models describing a single two-level system coupled to two boson field modes in either a parallel or orthogonal configuration. Both models may be feasible for experimental realization through Raman adiabatic driving in cavity QED. We study their ground state configurations; that is, we find the quantum precursors of the corresponding semi-classical phase transitions. We found that the ground state configurations of both models present the same critical coupling as the quantum Rabi model. Around this critical coupling, the ground state goes from the so-called normal configuration with no excitation, the qubit in the ground state and the fields in the quantum vacuum state, to a ground state with excitations, the qubit in a superposition of ground and excited state, while the fields are not in the vacuum anymore, for the first model. The second model shows a more complex ground state configuration landscape where we find the normal configuration mentioned above, two single-mode configurations, where just one of the fields and the qubit are excited, and a dual-mode configuration, where both fields and the qubit are excited. [Preview Abstract] |
(Author Not Attending)
|
G1.00235: Quantum Phase Slip Localization on the Percolation Cluster Backbone Noah Bray-Ali Quantum phase slips proliferate at the superfluid-to-Mott insulator transition of interacting lattice bosons with commensurate filling in one dimension. The backbone of the incipient infinite cluster at percolation threshold is topologically one-dimensional but localizes quantum phase slips. We calculate the quantum depletion of the condensate fraction on the percolation cluster for weak interactions. Finally we estimate the critical interaction strength where quantum phase slips delocalize using a strong-disorder renormalization group approach applied to the percolation backbone. [Preview Abstract] |
|
G1.00236: Quantum-coherence driven self-organized criticality and non-equilibrium light localization. Pankaj Jha, Kosmas Tsakmakidis, Yuan Wang, Xiang Zhang In its 28 years since its introduction in 1987, self-organized criticality (SOC) has had a major impact across a broad range of seemingly dissimilar fields of science. However, until now, it has primarily been applied to classical systems, and it remains a fundamental open question whether the theory also finds a place in complex systems driven by quantum coherence (QC). Here, on the basis of a many-body quantum-field theory and corroborating Maxwell-Bloch-Langevin computations, we report on the first example of fractal SOC driven, in the nano-world, by quantum coherence. We show that a quantum-coherently controlled active nano-plasmonic heterostructure allows, in the regime where the light speed is very close to zero, for the phase-synchronization in space of a continuous ensemble of nano-optical oscillators, giving rise to a fundamentally new kind of non-equilibrium light localization. We observe all hallmarks of SOC in this quantum many-body photonic nano-system of interacting heavy bosons, and we identify two critical points, one signifying the onset of spontaneous spatial self-organization, followed in time by another one that signifies the onset of activity. Our analysis reveals a quantum-coherence driven self-organized double-critical property in photonics and a new type of robust light localization, far out of thermodynamic and optical equilibria, with a broad range of potential applications in nano-optics and condensed-matter photonics. [Preview Abstract] |
|
G1.00237: Anomalous diffusion of light in complex media Roxana Rezvani Naraghi, Marielena Burdge, Aristide Dogariu Light propagation in random materials is often modeled by a diffusion approximation to the radiation transfer equation. This approach inherently ignores interference effects and describes only the energy propagation. When the interaction is strong, however, the scattering events become correlated and wave interferences can cause the diffusion to be slow down. One result of this process is the appearance of localized modes, whereby the energy inside the material is confined to small spatial regions due to constructive interferences. This anomalous, sub-diffusive character of energy propagation could be justified within the scaling theory of localization where the optical diffusion coefficient is size dependent. Moreover, when the concentration of scatterers increases, the near-field interactions between scatterers placed in close proximity of each lead to a new transport regime. In these conditions, the energy spread is not only diffusive but it also evolves through evanescent coupling between individual scatterers. Based on measurements of photon path-length distributions, we report the observation of such distinct regimes of energy transport. [Preview Abstract] |
|
G1.00238: Topological photonics: an observation of Landau levels for optical photons Nathan Schine, Albert Ryou, Ariel Sommer, Jonathan Simon We present the first experimental realization of a bulk magnetic field for optical photons. By using a non-planar ring resonator, we induce an image rotation on each round trip through the resonator. This results in a Coriolis/Lorentz force and a centrifugal anticonfining force, the latter of which is cancelled by mirror curvature. Using a digital micromirror device to control both amplitude and phase, we inject arbitrary optical modes into our resonator. Spatial- and energy- resolved spectroscopy tracks photonic eigenstates as residual trapping is reduced, and we observe photonic Landau levels as the eigenstates become degenerate. We show that there is a conical geometry of the resulting manifold for photon dynamics and present a measurement of the local density of states that is consistent with Landau levels on a cone. While our work already demonstrates an integer quantum Hall material composed of photons, we have ensured compatibility with strong photon-photon interactions, which will allow quantum optical studies of entanglement and correlation in manybody systems including fractional quantum Hall fluids. [Preview Abstract] |
|
G1.00239: Topological $Z_2$ Gapless Photonic Crystals Biye Xie, Zidan Wang Topological properties of electronic materials with gapless band structure such as Topological Semimetals(TSMs) and Topological Metals(TMs) have drew lots of attention to both theoretical and experimental physicists recently. Although theoretical prediction of TSMs and TMs have been done well, experimental study of them is quite difficult to perform due to the fact that it is very difficult to control and design certain electronic materials. However, since the topological properties stem from the geometric feature, we can study them in Photonic Crystals(PhCs) which are much easy to be controlled and designed. Here we study 2-dimension PhCs consisting of gyrotropic materials with hexagonal structure. In the Brillouin corner, the dispersion relation has gapless points which are similar to Dirac Cones in electronic materials. We firstly derive the effective Hamiltonian of this system and show that if certain perturbation is added to this effective Hamiltonian, this system belongs to AII class according to Altland and Zirbauer topological classification and is described by a $Z_2$ topological charge. Finally we also propose a way to detect this $Z_2$ topological charge using momentum space Aharonov-Bohm interferometer which is firstly proposed by L.Duca and T.Li,etc. [Preview Abstract] |
|
G1.00240: Real-time emission spectrum from a hybrid atom-optomechanical cavity Imran Mirza Hybrid quantum systems are promising candidates for opening new avenues for quantum technologies [G. Kurizki et. al, PNAS, 112 (13), 3866-3873 (2015)]. Hybrid atom-optomechanical (HAOM) systems set an intriguing example in this context. From the perspective of practical utilizations of these HAOM systems in future quantum devices, it is crucial to fully understand the excitation dynamics as well as the spectral features of these systems. In this poster, I'll present my calculations of single-photon time-dependent (TD) spectrum emitted by such a HAOM system in a strong atom-cavity as well as strong cavity-mechanics (strong-strong) coupling regime [``Real-time emission spectrum from a hybrid atom-optomechanical cavity'', Imran M. Mirza, J. Opt. Soc. Am. B, 32 (8), 1604-1614 (2015)]. In order to make the system more realistic the effects of dissipation through the mechanical oscillator, optical cavity and spontaneous emission from the two-level emitter are also incorporated. The TD spectrum reveals some novel features that are not possible to observe otherwise. For instance, time order in which different side bands appears which explains different photon-phonon interactions responsible for the production of distinct spectral resonances. . [Preview Abstract] |
|
G1.00241: Cooling a nanomechanical resonator using spin-dependent transport and noise interference in Andreev reflections Pascal Stadler, Wolfgang Belzig, Gianluca Rastelli Nanoelectromechanical systems promise to manipulate mechanical motion in the quantum regime using electron transport. For such a goal, a necessary condition is the ability of cooling the resonator into or near to its quantum ground state. A still open challenge in this field is the achievement of active cooling using purely electron transport in, for instance, suspended carbon nanotube quantum dots. We consider the quantum transport in a carbon nanotube quantum dot suspended between two electric nanocontacts. Due to the interaction between electrons and flexural mechanical modes, the electron transport results in inelastic vibration-assisted tunneling processes. These give rise to a mechanical damping and to a steady nonequilibrium phonon occupation of the resonator. We discuss these effects for two different coherent transport regimes: (i) spin-polarized current between two ferromagnets [1,2] and (ii) subgap Andreev current between a superconductor and normal metal [3]. \newline [1] P. Stadler, W. Belzig, and G. Rastelli, Phys. Rev. Lett. 113, 047201 (2014) \newline [2] P. Stadler, W. Belzig, and G. Rastelli, Phys. Rev. B 91, 085432 (2015) \newline [3] P. Stadler, W. Belzig, and G. Rastelli, arXiv:1511.04858 (submitted) [Preview Abstract] |
|
G1.00242: Transient Loschmidt Echo and Orthogonality Catastrophe in highly excited Quantum Ising Spin Chains Marco Schiro, Carla Lupo We study the response to sudden local perturbations of highly excited Quantum Ising Spin Chains. The key quantity encoding this response is the overlap between time-dependent wave functions, which we write as a transient Loschmidt echo. We compute the Echo perturbatively in the case of a weak local quench and study its asymptotics at long times, which contains crucial information about the structure of the highly excited non-equilibrium environment induced by the quench. Our results reveal that the Echo decays exponentially, rather than power law as in the low-energy Orthogonality Catastrophe, a further example of quench-induced decoherence. The emerging decoherence scale is set by the strenght of the local potential and the bulk excitation energy. In addition, the transient evolution features aging behavior at the Ising quantum critical point. [Preview Abstract] |
|
G1.00243: Minimally entangled typical thermal states versus matrix product purifications for the simulation of equilibrium states and time evolution Moritz Binder, Thomas Barthel We compare matrix product purifications and minimally entangled typical thermal states (METTS) for the simulation of equilibrium states and finite-temperature response functions of strongly correlated quantum many-body systems. For METTS, we highlight the interplay of statistical and DMRG truncation errors, discuss the use of self-averaging effects, and describe schemes for the computation of response functions. We assess the computation costs and accuracies of the two methods for critical and gapped spin chains and the Bose-Hubbard model. For the same computation cost, purifications yield more accurate results than METTS except for temperatures well below the system’s energy gap. (Phys. Rev. B 92, 125119 (2015)) [Preview Abstract] |
|
G1.00244: Investigation of the coupling of the momentum distribution of a BEC with its collective of modes Emanuel Henn, Pedro Tavares, Amilson Fritsch, Franklin Vivanco, Gustavo Telles, Vanderlei Bagnato In our group we have a strong research line on quantum turbulence and the general investigation of Bose-Einstein condensates (BEC) subjected to oscillatory excitations. Inside this research line we investigate first the behavior of the normal modes of the BEC under this excitation and observe a non-linear behavior in the amplitude of the quadrupolar mode. Also, inside this same procedure of investigation we study the momentum distribution of a BEC to understand if it is possible to extract Kolmogorov like excitation spectra which would point to a turbulent state of matter. The condensate is perturbed, and we let it evolve in-trap after which we perform standard time-of- flight absorption imaging. The momentum distribution is extracted and analyzed as a function of the in-trap free evolution time for a 2D projected cloud. We show that the momentum distribution has its features varying periodically with the same frequency as the quadrupolar mode displayed by the atomic gas hinting at a strong coupling of both. The main consequence of that one cannot be assertive about the quantitative features of the extract spectrum of momentum and we can only rely on its qualitative features. [Preview Abstract] |
|
G1.00245: One-dimensional Bose-Einstein condensation of photons in a microtube Alex Kruchkov This study introduces a quasiequilibrium one-dimensional Bose-Einstein condensation of photons trapped in a microscopical waveguide. Light modes with a cut-off frequency ("photon's mass") interact through different processes of absorption, re-emition, and scattering on molecules of dye. In this work I consider conditions for the one-dimensional condensation of light and the role of photon-photon interactions in the system. The computational technique in use is the Matsubara's Green's functions formalism modified for the quasiequilibrium system under study. [Preview Abstract] |
|
G1.00246: Spontaneous Exciton Condensate in Transition Metal Dichalcogenides electron-hole bilayer System Bishwajit Debnath, Yafis Barlas, Darshana Wickramaratne, Mahesh Neupane, Roger Lake Spontaneous Bose-Einstein Exciton condensation (BEC) in spatially separated graphene layers has received intense theoretical and experimental attention, due to its promise for low-dissipation electronic devices. We have investigated BN-separated monolayers of transition metal dichalcogenides (TMDs) to explore the possibility of achieving exciton superfluidity in this class of 2D materials. The top and bottom monolayers can consist of either same TMD (homo-bilayer) or a combination of different TMDs (hetero-bilayer). The particle density in each monolayer is tuned by independent gate biasing. In TMDs, the almost equivalent particle-hole symmetry is an assisting factor towards achieving condensation. The calculated exciton binding energies are found to be as large as 50 -- 250 meV, which is a result of the large effective masses in the TMDs. For BN thicknesses of around 3nm, the interaction strength is large and no longer in the weak coupling regime. Therefore, to calculate the excitonic gap, we use a modified Eliashberg formalism in which the phonon-mediated interaction is replaced with the inter-layer screened coulomb interaction between TMD bilayers. [Preview Abstract] |
|
G1.00247: Josephson Effect in Trapped Spin-orbit Coupled Bose-Einstein Condensation Wai Ho Tang Spin-orbit coupling (SOC) has given rise to many novel states of matter including topological insulators and superconductors. Recent experimental realization of SOC in neutral cold atom systems have opened a new avenue to study its effects in Bose-Einstein condensate. In this study, we discuss the Josephson-like mode in the spin-orbit coupled condensate, and study its decoherence due to thermal effect. We discuss experimental implications of our results. [Preview Abstract] |
|
G1.00248: Entanglement like properties in Spin-Orbit Coupled Ultra Cold Atom and violation of Bell like Inequality Sankalpa Ghosh, Rahul Kumar We show that the general quantum state of synthetically spin-orbit coupled ultra cold bosonic atom whose condensate was experimentally created recently ( Y. J. Lin {\it et al.}, Nature, {\bf 471}, 83, (2011)), shows entanglement between motional degrees of freedom ( momentum) and internal degrees of freedom (hyperfine spin). We demonstrate the violation of Bell-like inequality (CHSH) for such states that provides a unique opportunity to verify fundamental principle like quantum non-contextuality for commutating observables which are not spatially separated. We analyze in detail the Rabi oscillation executed by such atom-laser system and how that influneces quantities like entanglement entropy, violation of Bell like Inequality etc. We also discuss the implication of our result in testing the quantum non-contextuality and Bell's Inequality vioaltion by macroscopic quantum object like Bose-Einstein Condensate of ultra cold atoms. [Preview Abstract] |
|
G1.00249: Measurement of optical nonlinearity of highly dispersive medium using optical heterodyne detection technique Arup Bhowmick, Ashok Mohapatra We discuss the optical heterodyne detection technique to study the absorption and dispersion of a probe beam propagating through a medium with a narrow resonance. The technique has been demonstrated for Rydberg Electro-magnetically induced transparency (EIT) in rubidium thermal vapor and the optical non-linearity of a probe beam with variable intensity is studied. A quantitative comparison of the experimental result with a suitable theoretical model is presented. The limitations and the working regime of the technique are discussed. [Preview Abstract] |
|
G1.00250: Pair condensation of a spin-imbalanced two-dimensional Fermi gas Debayan Mitra, Peter Brown, Stanimir Kondov, Peter Schauss, Waseem Bakr Strongly interacting Fermi gases of ultracold atoms are a clean and tunable platform for exploring high critical temperature superfluidity. This is particularly interesting because the physics of these gases has a close connection to superconductivity in strongly correlated materials. Early experiments in 3D gases have shed light on the crossover from BCS superfluidity to Bose-Einstein condensation of molecules and on the fate of superfluidity in spin-imbalanced gases. Here we study a strongly-interacting spin-imbalanced Fermi gas in two dimensions, where the low dimensionality enhances correlations and phase fluctations in the gas. We observe pair condensation in the imbalanced gas and map out the temperature-polarization phase diagram for a range of interactions strengths. At low temperatures, we observe phase separation between the superfluid and the normal gas over a wide range of imbalance. The measurement of the phase diagram of strongly interacting fermions in two dimensions opens the door for a detailed investigation of exotic phases enhanced in two dimensions and in optical lattices like the elusive FFLO phase. [Preview Abstract] |
|
G1.00251: Supersolidity in the one-dimensional Bose-Hubbard Model B. TANATAR, B. HETENYI We show how a variational Monte Carlo method can be constructed based on the Baeriswyl wavefunction to calculate the ground-state properties of one-dimensional Bose-Hubbard model. The phase diagram obtained is in excellent agreement with previous quantum Monte Carlo results. We also investigate the sensitivity of the system to a boundary twist, and find that it is sizeable even for integer fillings. To understand the nature of the phase we use a single-particle and a many-particle localization quantity and find that at integer fillings the system exhibits many-particle localization, at the same time, single particles as a result of bosonic exchange, can delocalize over the entire lattice. Away from integer fillings, where the system is known to be superfluid, delocalization is found at both the single-particle and many-particle level. We interpret these results as a signature of supersolidity in the Bose-Hubbard model at integer filling. [Preview Abstract] |
|
G1.00252: A spinor boson AB chain . Greis Julieth Cruz Reyes, Roberto Franco, Jereson Silva Valencia Recent research is focused on superlattices arising from optical lattices, which allow a tunable environment. Experimentally bosons present transitions from superfluid to Mott insulator by changing the energy offset in the unit cell [Nat. Commun. 5:5735 (2014)]. Many studies displayed that ground state of spinless boson systems on superlattices present superfluid, Mott insulator and an additional CDW phase created by the energy shift between the sites into the unit cell [Phys. Rev. A 83, 053621 (2011)]. The first confinement methods were magnetic traps, which freezes the spin; with optical lattices the grade of freedom of spin plays an important role. We consider bosons with spin S$=$1 on a superlattice made by two sites with energy offset per unit cell (AB chain). The Hamiltonian that describes the system is the Bose-Hubbard model with the superlattice potential (W) and the exchange interaction (V) parameters. This model supports CDW, Mott insulator and superfluid phases. For W near to U, with V$=$0, Mott phase disappears, but for V increasing, a new CDW appears due to the spin interaction, while the half-integer CDW~decrease. These results are widely different from spinless boson, where the CDW phases are stables. [Preview Abstract] |
|
G1.00253: Bose-Hubbard Model on Penrose Tilling Lattice Johnson Chan, Dimitrios Galanakis The standard Bose-Hubbard model has provided a paradigmatic example to explore the quantum phases in a strongly interacting boson system. However, studies so far have considered lattice models with the conventional lattice symmetry (square, triangular, honeycomb etc. in two dimensions), and very few studies in the case of a quasi-crystal. Experimentally, quasi-crystal optical lattices have been realized in the experiments and this provides a very timely opportunity to investigate the possible quantum states of a Bose-Hubbard model in a quasi-crystal. In our work, we performed the first Quantum Monte Carlo of Bose-Hubbard model on a Penrose tilling lattice at finite temperature. We compute the phase diagram and investigate the behavior of phase transitions by looking at several observables, including momentum distribution, distribution of condensate fraction and density distributions. Our work can be checked in future experiments. [Preview Abstract] |
|
G1.00254: Photoelectric devices with quantum coherence. Su Shanhe A phtotoelectric device consisting of a three-level system contacted with two fermionic baths and a photon bath is built. Making the Born-Markov approximation, the equation of motion for the density operator in a Lindblad-like form is derived. We obtain the coherence and the efficiency of the system under the steady-state condition. Results show that quantum coherence can enhance the photoelectric conversion efficiency. The efficiency at maximum power can be larger than the CA efficiency bound with the existence of coherence. [Preview Abstract] |
|
G1.00255: Spectral singularity in composite systems and simulation of laser resonant chamber Xizheng Zhang A non-Hermitian system with spectral singularity (SS) exhibits fascinating phenomena which never appear in a Hermitian system. We investigate the existence of SS for a composite system which is consisted of two separated scattering centers A and B embedded in a one-dimensional free space, one of which is non-Hermitian at last. We show that the composite system has a SS at $k_{c} $ if the reflection amplitudes $r^{A}\left( {k_{c} } \right)$ and $r^{B}\left( {k_{c} } \right)$ of two scattering centers satisfy the condition $r_{\mbox{R}}^{A} \left( {k_{c} } \right)r_{\mbox{L}}^{B} \left( {k_{c} } \right)e^{i2k_{c} \left( {x_{B} -x_{A} } \right)}=1$, based on the theorem proposed by Ali (PRL 102, 220402 (2009)). Multi-scattering-centers generalization of the theorem is also obtained. As an application, we construct a simple system to simulate the resonant chamber for generating laser light. [Preview Abstract] |
|
G1.00256: Dark state in a nonlinear optomechanical system with quadratic coupling Yue-Xin Huang, Xiang-Fa Zhou, Guang-Can Guo, Yong-Sheng Zhang We consider a hybrid system consisting of a cavity optomechanical device with nonlinear quadratic radiation pressure coupled to an atomic ensemble. By considering the collective excitation, we show that this system supports nontrivial, nonlinear dark states. The coupling strength can be tuned via the lasers that ensure the population transfer adiabatically between the mechanical modes and the collective atomic excitations in a controlled way. In addition, we show how to detect the dark-state resonance by calculating the single-photon spectrum of the output fields and the transmission of the probe beam based on two-phonon optomechanically induced transparency. Possible application and extension of the dark states are also discussed. [Preview Abstract] |
|
G1.00257: Bose gas with generalized dispersion relation plus an energy gap M. A. Solis, J. G. Martinez, J. Garcia We report the critical temperature, the condensed fraction, the internal energy and the specific heat for a $d$-dimensional Bose gas with a generalized dispersion relation plus an energy gap, i.e., $\varepsilon=\varepsilon_0$ for $k=0$ and $\varepsilon=\varepsilon_0 +\Delta+ c_sk^s$, for $k>0$, where $\hbar k$ is the particle momentum, $\varepsilon_0$ the lowest particle energy, $c_s$ a constant with dimension of energy multiplied by a length to the power $s > 0$. When $\Delta > 0$, a Bose-Einstein critical temperature $T_c \neq 0$ exists for any $d/s \geq 0$ at which the internal energy shows a peak and the specific heat shows a jump. The critical temperature and the specific heat jump increase as functions of the gap but they decrease as functions of $d/s$. Thermodynamic properties are $\varepsilon_0$ independent since this is just a reference energy. For $\Delta = 0$ we recover the results reported in Ref. [1].\\ [1] V. C. Aguilera-Navarro, M. de Llano y M. A. Sol\'is, Eur. J. Phys. {\bf 20}, 177 (1999). [Preview Abstract] |
|
G1.00258: Derivation and Inter-relationship of Planck time, the Hubble constant, and Cosmic Microwave Background Radiation from the Neutron and the Quantum Properties of Hydrogen D. W. Chakeres, R. Vento, S. S. Moses, J. B. Sauza, V. M. Andrianarijaona Planck time, t$_{\mathrm{P}}$, is presently the only fundamental constant that unites the physical domains of c, h, and G, and is therefore a globally defined normalized time constant. This study shows a method to derive t$_{\mathrm{P}}$, H$_{\mathrm{0}}$, G, and the Cosmic Microwave Background Radiation (CMBR) peak spectral radiance from the frequency equivalents of the neutron and the quantum properties of hydrogen such as Rydberg's constant, Bohr radius, electron mass and electron charge. All of the derivations are within the experimental ranges, including errors. Moreover, these results exceed what is experimentally possible because the natural unit data are of high precision. The constants are evaluated within a combined classic integer and harmonic fraction, power law relationship. The logarithmic base of the annihilation frequency of the neutron, approximately 2.27 \texttimes 10$^{\mathrm{23}}$ Hz, scales the independent axis to an integer and partial harmonic fraction system. The dependent axis is scaled by the properties of hydrogen. On the line that defines Planck time squared, t$_{\mathrm{P}}^{\mathrm{2}}$, there exist unique points directly related to H$_{\mathrm{0}}$, and the CMBR. Therefore these three fundamental cosmic constants are mathematically and conceptually closely inter-related, and each derivable from the others. [Preview Abstract] |
|
G1.00259: Strong Field QED Simulation of Laser-Plasma Interaction Using BUMBLEBEE. Xiaolin Jin, Yunxian Tian, Tao Huang, Wenlong Chen, Bin Li Next generation laser intensity could reach 10$^{24}$ W/cm$^{2}$, making strong field quantum electrodynamics (QED) effects in laser-plasma interaction a promising research field. The model of photon and pair production in strong field QED is implemented into our 1D3V particle-in-cell (PIC) code BUMBLEBEE with Monte Carlo (MC) algorithm. We apply the kirk and bell model to simulate the photon and pair production, where photon is produced through bremsstrahlung process and the pair is produced through the Bethe-Heitler process. There are two stages in the QED pair production process. Firstly, the intense laser interacts with a relativistic electron or positron to produce the photon. Secondly, the photon interacts with the same laser field to produce the e$^{+}$-e$^{-}$ pair. The QED process is coupled to laser-plasma interaction processes before pushing the particles at each step. Using this code, the evolutions of the particles in ultrahigh intensity laser (\textasciitilde 10$^{23}$W/cm$^{2})$ interaction with aluminum foil target are observed. Four different initial plasma profiles are considered in the simulations. [Preview Abstract] |
|
G1.00260: A~Control Based~System of Mechanical Loss~Measurement for High Quality Factor Oscillators Louis Louis Gitelman, Nicolas Smith, Isaac Jafar, Gregory Harry, Jonathan Newport, Matt Abernathy In this poster we will present the control system being developed to measure the quality factor of optics used in the Advanced LIGO gravitational wave detectors to predict thermal noise levels. It works by locking the phase between the optic's exciter and normal mode to pi/2 and locking the optics's amplitude allowing one to equate the energy output of the exciter to the mechanical loss of the optic. To do this the amplitude of the normal mode is detected using a birefringence meter and lockin amplifier, which is then fedback to an electrostatic exciter to control the mode's amplitude and phase with a PID controller written on a python script. The poster will discuss the components and assembly of this system and the theoretical control structure behind it. It will also discuss the speed, accuracy and general feasibility of this method of quality factor measurement relative to other methods, and steps to improve and develop this method of quality factor measurement and the possible applications for LIGO and in general. [Preview Abstract] |
|
G1.00261: ABSTRACT WITHDRAWN |
|
G1.00262: Abnormal Dispersion of Optical Modes in a non-Hermitian system: Feasibility and Applications Jing Chen, Ruipeng Guo, Liting Wu We analyze the dispersions of optical eigen-modes in a non-Hermitian system. We show that abnormal dispersion of optical modes can be realized by using the concept of optical parity-time symmetry. Physical significance of these effects is discussed. The feasibility in realizing these abnormal dispersions in passive systems and the connection with damped polaritons in various photonic and phononic systems are discussed. This investigation can find many attractive applications in manipulating the dynamic of coupled optical waves, if the parasite tradeoff of loss effect can be relieved by proper gain effects. [Preview Abstract] |
|
G1.00263: Optical tweezers theory near a flat surface: a perturbative method Henrik Flyvbjerg, Rafael S. Dutra, Paolo A. Maia Neto, H. Moyses Nussenzveig We propose a perturbative calculation of the optical force exercised by a focused laser beam on a microsphere of arbitrary radius that is localized near a flat glass surface in a standard optical tweezers setup. Starting from the Mie-Debye representation for the electric field of a Gaussian laser beam, focused by an objective of high numerical aperture, we derive a recursive series that represents the multiple reflections that describe the reverberation of laser light between the microsphere and the glass slide. We present numerical results for the axial component of the optical force and the axial trap stiffness. Numerical results for a configuration typical in biological applications—a microsphere of 0.5 µm radius at a distance around 0.25 µm from the surface—show a 37% correction due to reverberation effects in relation to MDSA theory [1]. This calls for absolute calibration [2] in this typical situation. [1] Viana N B, Rocha M S. Mesquita O N, et al. (2007) Towards absolute calibration of optical tweezers. Phys Rev E 75:021914-1–14. [2] Dutra R S, Viana N B, Maia Neto P A, et al. (2014) Absolute calibration of forces in optical tweezers. Phys Rev A 90:013825-1–13. [Preview Abstract] |
|
G1.00264: Hard X-ray Pump, X-ray Probe Spectroscopy of Single Crystals. Aaron Loether, Matt DeCamp, Donald Walko Recent advancements in intense x-ray pulses have made it possible to perform hard x-ray pump probe spectroscopy. Inspired by optical pump probe, we've built a retroreflector for use with synchrotron based x-rays, using Germanium crystals at Bragg condition in place of mirrors, to control relative timing of x-ray pulses and perform time resolved measurements. Testing of multiple versions of the retroreflector was done both experimentally and via simulation; the comparison allows us to show efficiencies achievable theoretically and realistically. A proof of concept time resolved diffraction experiment on a Germanium 111 crystal was performed utilizing high intensity broadband x-ray pulses and the resulting heating and propagated strains were measured by low intensity monochromatic x-ray pulses. [Preview Abstract] |
|
G1.00265: Observations of the high vibrational levels of the $B''BÊ^{1}\Sigma_{u}^{+} $state of H$_{2}$ Robert Ekey, Alexander Chartrand, Wenqi Duan, Elizabeth McCormack Double-resonance laser spectroscopy via the $EFÊ^{1}\Sigma_{g}^{+} ,Êv'=6,ÊJ'=0-2$state was used to probe the high vibrational levels of the $B''BÊ^{1}\Sigma_{u}^{+} $ state of molecular hydrogen. Resonantly-enhanced multiphoton ionization spectra were recorded by detecting ion production as a function of energy using a time of flight mass spectrometer. New measurements of energies for the v $=$ 51 $-$ 66 levels for the $B''BÊ^{1}\Sigma_{u}^{+} $ state are reported, which, taken with previous results, span the v $=$ 46 $-$ 69 vibrational levels. Results for energy levels are compared to theoretical calculations [L. Wolniewicz, T. Orlikowski, and G. Staszewska, J. Mol. Spec. 238, 118 (2006)]. The average difference between the 84 measured energies and calculated energies is $-$3.8 cm$^{-1}$ with a standard deviation of 5.3 cm$^{-1}$ . This level of agreement showcases the success of the theoretical calculations in accounting for the strong rovibronic mixing of the$^{1}\Sigma_{u}^{+} $and $^{1}\Pi_{u}^{+} $states. [Preview Abstract] |
|
G1.00266: ABSTRACT WITHDRAWN |
|
G1.00267: QUANTUM INFORMATION, CONCEPTS AND COMPUTATION |
|
G1.00268: Geometric Decompositions of Bell Polytopes with Practical Applications Peter Bierhorst In the well-studied (2,2,2) Bell experiment consisting of two parties, two measurement settings per party, and two possible outcomes per setting, it is known that if the experiment obeys no-signaling constraints, then the set of admissible experimental probability distributions is fully characterized as the convex hull of 24 distributions: 8 Popescu-Rohrlich (PR) boxes and 16 local deterministic distributions. Here, we refine this result to show that in the (2,2,2) case, any nonlocal nonsignaling distribution can always be uniquely expressed as a convex combination of exactly one PR box and (up to) eight local deterministic distributions. In this representation each PR box will always occur only with a fixed set of eight local deterministic distributions with which it is affiliated. This decomposition has multiple applications: we demonstrate an analytical proof that the minimum detection efficiency for which nonlocality can be observed is 2/3 even for theories constrained only by the no-signaling principle, and we develop new algorithms that speed the calculation of important statistical functions of Bell test data. Finally, we enumerate the vertices of the no-signaling polytope for the (2, n, 2) ``chained Bell'' scenario and find that similar decomposition results are possible in this general case. Here, our results allow us to prove the optimality of a bound, derived in (Barrett et al., PRL, 2006) on the proportion of local theories in a local/nonlocal mixture that can be inferred from the experimental violation of a chained Bell inequality. [Preview Abstract] |
|
G1.00269: Implementing entangling gates via quantum walks through branching graphs. Dmitry Solenov, Thomas Cavin Efficient quantum gates are essential to quantum computing. It was found recently that quantum walks can enhance performance of quantum gates. We investigate how the propagation of a complicated, branching system can be solved analytically by first mapping it to linear chain. We found that certain types of systems, including systems of n qubits, can be algorithmically mapped to a system of disjoint linear chains. In particular, we found a solution for the 3 qubit system that performs either a trivial return walk or a return walk with a phase of pi introduced. [Preview Abstract] |
|
G1.00270: Error Threshold for the 4.6.12 Topological Color Code Colin Trout Topological color codes are interesting candidates for fault-tolerant quantum computation. Relative to surface codes, color codes have a larger set of transversal gates, which reduces the resources required for state distillation to achieve universal quantum computation. Here we study a family of color codes defined by the 4.6.12 semi-regular lattice. We adapt a minimum weight perfect matching decoder to report an error threshold for the 4.6.12 topological color code under the circuit-based error model. [Preview Abstract] |
|
G1.00271: Growth of single-crystal Al layers on GaAs and Si substrates for microwave superconducting resonators J Tournet, D Gosselink, M Jaikissoon, G-X Miao, D Langenberg, M Mariantoni, ZR Wasilewski Thin Al layers on dielectrics are essential building blocks of circuits used in the quest for scalable quantum computing systems.~While molecular beam epitaxy (MBE) has been shown to produce the highest quality Al layers, further reduction of losses in superconducting resonators fabricated from them is highly desirable. Defects at the Al-substrate interface are likely the key source of losses. Here we report on the optimization of MBE growth of Al layers on GaAs and Si substrates. Si surfaces were prepared by \textit{in-situ} high temperature substrate annealing. For GaAs, defects typically remaining on the substrate surfaces after oxide desorption were overgrown with GaAs or GaAs/AlAs superlattice buffer layers. Such surface preparation steps were followed by cooling process to below 0\textdegree C, precisely controlled to obtain targeted surface reconstructions. Deposition of 110~nm Al layers was done at subzero temperatures and monitored with~RHEED at several azimuths simultaneously. The resulting layers were characterized by HRXRD, AFM and Nomarski. Single crystal, near-atomically smooth layers of Al(110) were demonstrated on GaAs(001)-2x4 surface whereas Al(111) of comparable quality was formed on Si(111)-1x1 and 7x7 surfaces. [Preview Abstract] |
|
G1.00272: Macroscopic Quantum Superposition in Cavity Optomechanics Jie-Qiao Liao, Lin Tian Quantum superposition in mechanical systems is not only a key evidence of macroscopic quantum coherence, but can also be utilized in modern quantum technology. Here we propose an efficient approach for creating macroscopically distinct mechanical superposition states in a two-mode optomechanical system. Photon hopping between the two cavity-modes is modulated sinusoidally. The modulated photon tunneling enables an ultrastrong radiation-pressure force acting on the mechanical resonator, and hence significantly increases the mechanical displacement induced by a single photon. We present systematic studies on the generation of the Yurke-Stoler-like states in the presence of system dissipations. The state generation method is general and it can be implemented with either optomechanical or electromechanical systems. [Preview Abstract] |
|
G1.00273: Generation of macroscopic Schroedinger's cat states in qubit-oscillator systems Jin-Feng Huang, Jie-Qiao Liao, Lin Tian We study a scheme to generate macroscopic Schroedinger’s cat states in a quantum oscillator (electromagnetic field or mechanical resonator) coupled to a quantum bit (two-level system) via a conditional displacement mechanism. By driving the qubit monochromatically, the oscillation of the qubit state modifies the effective frequency of the driving force acting on the oscillator, and a resonant or near resonant driving on the oscillator can be achieved. The displacement of the oscillator is then significantly enhanced due to the small detuning of the driving force and can exceed that of the zero-point fluctuation. This effect can be used to prepare quantum superpositions of macroscopically distinct coherent states in the oscillator. We present detailed studies on this state generation scheme in both closed and open system cases. This approach can be implemented in various experimenta [Preview Abstract] |
|
G1.00274: Towards Quantum Simulation of Chemical Dynamics with Prethreshold Superconducting Qubits A.W. Cook, P.C. Stancil, M. Geller, Hao You, A.T. Sornborger While large-scale, fault-tolerant quantum computing devices are still on the horizon, considerable activity has focused on quantum simulation (qs). While advances have been made in realizing both digital and analog qs, the former is still restricted by the need for fault-tolerant computational qubits. As an alternative, we are exploring the single excitation subspace (ses) approach which has the advantage of using today's prethreshold devices and can function as a schroedinger equation solver. One application of the ses method is the study of molecular collision problems. we are both developing efficient, optimized scattering approaches on classical computers and porting the method to an ses processor focusing on superconducting architectures. Issues related to propagator efficiency, multichannel potential averaging, and ehrenfest symmetrization have been explored. Results from classical calculations and simulations of qs for ion-atom collisions will be presented. [Preview Abstract] |
|
G1.00275: A Quantum Electrodynamics Kondo Circuit with Orbital and Spin Entanglement Marco Schiro, Guang-Wei Deng, Loic Henriet, Da Wei, Shu-Xiao Li, Hai-Ou Li, Gang Cao, Ming Xiao, Guang-Can Guo, Karyn Le Hur, Guo-Ping Guo Recent progress in nanotechnology allows to engineer hybrid mesoscopic devices comprising on chip an artificial atom or quantum dot, capacitively coupled to a microwave (superconducting) resonator and to biased metallic leads. Here, we build such a prototype system where the artificial atom is a graphene double quantum dot (DQD) to probe non-equilibrium aspects of strongly-entangled many body states between light and matter at the nanoscale. Controlling the coupling of the photon field and the charge states of the DQD, we measure the microwave reflection spectrum of the resonator. When the DQD is at the charge degeneracy points, experimental results are consistent with a Kondo impurity model entangling charge, spin and orbital degrees of freedom with the quantum fluctuations of the cavity photon. The light coming out from the resonator reveals the formation of the Kondo or Abrikosov-Suhl resonance at low temperatures. We also explore other routes to investigate nonlinear transport by increasing the microwave power, the bias and gate voltages. [Preview Abstract] |
|
G1.00276: Continuous Wave Noise Spectroscopy Beyond the Weak Coupling Limit Kyle Willick, Daniel Park, Jonathan Baugh The optimization of dynamical decoupling and quantum error correction for a particular qubit realization is based on a detailed knowledge of the noise properties. Spectroscopy of single-axis noise using dynamical decoupling pulse sequences has garnered much recent attention. In this work we consider noise spectroscopy based on a continuous-wave (CW) on-resonance driving field. Standard CW noise spectroscopy is limited to the weak coupling regime, in which the generalized Bloch equation (GBE) and filter function approaches are valid. We present a technique for extending the range over which the spectral density of the noise S($\omega$) can be reliably reconstructed to beyond the weak coupling limit, i.e. to frequencies small compared to the noise strength. The technique utilizes a numerical calculation of the short-time signal decay under the zeroth order average Hamiltonian to iteratively correct the estimated S($\omega$) at low frequencies. The results demonstrate faithful extraction of colored noise spectra to zero frequency, whereas naive application of the GBE fitting can significantly underestimate the low frequency noise power. [Preview Abstract] |
|
G1.00277: The Quantum-Classical Boundary for Optical Interferometric Measurements Patrick M. Birchall, Jonathan C. F. Matthews, Hugo Cable We study the fundamental precision limits for measurements of optical phase when loss of probe light dominates the decoherence, and a limited number of photons are passed through the sample. It has long-been argued that non-classical states can be used to achieve an important advantage in precision in measurements of this sort, where it is not possible to use high-power laser light. As well as being of fundamental interest for understanding the ultimate physical limits for precision measurement, there are practical applications to measurements of delicate or photosensitive samples. Here we compare optimal measurement strategies using classical and non-classical probe states, where the number of passes through the unknown phase can be freely controlled. We find that the increase in precision that can be achieved using non-classical techniques is in fact small. Our results narrow the potential applications of measurements using non-classical states to cases where there is greater quantum advantage due to practical constraints on the measurements involved. [Preview Abstract] |
|
G1.00278: ABSTRACT WITHDRAWN |
|
G1.00279: Experimental realization of optimal control with robustness to coupling errors Feihao Zhang, Guilu Long Optimal control theory is applied in quantum information processing for its ability to find objective evolution in complex quantum system. The negative factors, like the coupling to the environment, will impede the ideal evolution and increase their effect over time. In this work, we introduce a new method for finding objective propagator with robustness to coupling errors. The bath disturbance is analyzed by the time scale decomposition of spin dynamics. And the optimization is based on a gradient algorithm. We will give the experimental comparison between this robust optimal control method and the original one in spin system. Results show the advantage of this method in a noisy environment. [Preview Abstract] |
|
G1.00280: Nonlinear Effects in Coupled Microtoroidal Optical Microcavities Xiaofei Liu, Gui Lu Long Nonlinear effect plays an important role in modern physics. Thanks to the great improvement of the fabrication technology, the quality factor of microcavities can reach more than 100 million. This gives rise to many amazing phenomena. Recently, a new kind of nonlinear effect, optomechanics, which involves the interaction between the photon and phonon, has made important progress both in experiment and theory. Here, we will study the nonlinear effect in coupled microcavities, and three-way electromaganetic induced transparency and so on. [Preview Abstract] |
|
G1.00281: First-principles hyperfine tensors for electrons and holes in silicon and GaAs Pericles Philippopoulos, Stefano Chesi, William Coish Knowing (and controlling) hyperfine interactions in silicon and III-V semiconductor nanostructures is important for quantum information processing with electron and nuclear spin states. We have performed density-functional theory (DFT) calculations that fully account for spin structure of the Bloch states (in contast with approaches that rely on the density alone). Using this method, we confirm the known value for the contact hyperfine coupling in the conduction band of silicon, but find a significant deviation in the value for the conduction band of GaAs relative to the accepted value, estimated in ref. [1]. Moreover, this method can be used to calculate the full hyperfine tensor for the valence band, where spin-orbit effects may be strong, precluding methods that determine hyperfine couplings from the density alone. This general method can be applied to a broad class of materials with strong combined spin-orbit and hyperfine interactions. [1] D. Paget, G. Lampel, B. Sapoval, and V. I. Safarov Phys. Rev. B 15, 5780 (1977) [Preview Abstract] |
|
G1.00282: Hyperfine interaction mediated electric-dipole spin resonance: The role of the frequency modulation Rui Li The electron spin in semiconductor quantum dot can be coherently controlled by an external electric field, an effect called electric-dipole spin resonance (EDSR). There are several mechanisms underlie the EDSR, among which there is a hyperfine mechanism, where the spin-electric coupling is mediated by the electron-nucleus hyperfine interaction. Here, we investigate the influence of the frequency modulation (FM) to the driving electric field on the spin-flip efficiency. Our results reveal that FM plays an important role in the hyperfine mechanism. Without FM, the electric field almost cannot flip the electron spin, the spin-flip probability is only about 20{\%}. While under the FM, the spin-flip probability can be improved approximately to 70{\%}. Especially, we find there is a lower bound on the modulation amplitude, which is related to the width of the hyperfine field fluctuation of the nuclear spins. [Preview Abstract] |
|
G1.00283: Entangled Terahertz photon pair emitting diode with a HgTe quantum dot Li-Kun Shi, Kai Chang, Chang-Pu Sun We propose an experimentally feasible scheme for generating entangled terahertz photons in topological insulator quantum dots (TIQDs). We demonstrate theoretically that in TIQDs with disorders and irregular shapes: 1) the fine structure splitting, which is the obstacle to produce entangled photons in conventional semiconductor quantum dots, is inherently absent for one-dimensional massless excitons due to the time-reversal symmetry; 2) the selection rules obey winding number conservation instead of the conventional angular momentum conservation between edge states with a linear dispersion. With these two advantages, the entanglement of the emitted photons during the cascade in our scheme is robust against unavoidable disorders and morphology fluctuations of the TIQD. [Preview Abstract] |
(Author Not Attending)
|
G1.00284: Measure of the Quantum Speedup in Closed and Open systems Zhen-Yu Xu We construct a general measure for detecting the quantum speedup in both closed and open systems. This speed measure is based on the changing rate of the position of quantum states on a manifold with appropriate monotone Riemannian metrics. Any increase in speed is a clear signature of real dynamical speedup. To clarify the mechanisms of quantum speedup, we first introduce the concept of longitudinal and transverse types of speedup, and then apply the proposed measure to several typical closed and open quantum systems, illustrating that entanglement and the memory effect of the environment together can become resources for longitudinally or transversely accelerating dynamical evolution under certain conditions. Remarkably, a direct measurement of such speedup is feasible without the need for a tomographic reconstruction of the density matrix, which greatly enhances the feasibility of practical experimental tests. [Preview Abstract] |
|
G1.00285: Has Macroscopic Superposition in Superconducting Qubits Really Been Demonstrated? Alan M. Kadin, Steven B. Kaplan Quantum computing depends on many qubits coupled via quantum entanglement, where each qubit must be a simultaneous superposition of two quantum states of different energies, rather than one state or the other as in classical bits. It is widely believed that observations of energy quantization and Rabi oscillations in macroscopic superconducting circuits prove that these are proper qubits with quantum superposition. But is this really the only interpretration? We propose a novel paradigm for macroscopic quantum systems, in which energies are quantized (with photon-mediated transitions), but the quantized states are realistic objects without superposition. For example, a circuit could make a transition from one quantized value of flux to another, but would never have both at the same time. We further suggest a superconducting circuit that can put this proposal to a test [1]. Without quantum superposition, most of the potential benefit of quantum computing would be lost. [1] A.M. Kadin and S.B. Kaplan (2014), ``Superconducting Quantum Computing Without Entanglement?'', \underline {http://arxiv.org/abs/1408.5410}. [Preview Abstract] |
|
G1.00286: A local realistic model of quantum information systems explaining the four Bell states Jeffrey Boyd Can quantum computers and other information systems (like cryptography) be explained by local realism? The overwhelming consensus is NO. Thirty years of Bell test experiments proved Einstein, Podolsky and Rosen (EPR) wrong. Unknown to most physicists a new form of local realism has arisen, drastically different than EPR. The Theory of Elementary Waves (TEW) proposes that two entangled particles are both following the same elementary bi-ray. The same Bell test experiments that invalidate EPR, validate TEW. What is an elementary bi-ray? In TEW waves and particles usually travel in opposite directions. In entanglement experiments the picture is more complex. A bi-ray consists of two coaxial elementary rays, moving in opposite directions. Such bi-rays can explain all four Bell states on the basis of this peculiar form of local realism. Bell theory would classify TEW as “nonlocal,” even though it is local and realistic. The word “nonlocal” needs to be discarded, since “elementary bi-ray” is a more accurate and fertile descriptor of the same phenomena. TEW explains entanglement swapping heralding entanglement between distant spinning electrons in NV cavities, or trapped ions. The question is: So what? Would anything in quantum information science change if TEW were true? We think not. [Preview Abstract] |
|
G1.00287: Quantum Dualism: Hypermind? R. Jones Today the consensus view is that thought and mind is a combination of processes like memory, generalization, comparison, deduction, organization, analogy, etc. performed by classical computational machinery. (R. Jones, Trans. Kansas Acad. Sci., vol. 109, #3/4, 2006) But I believe quantum mechanics is a more plausible dualist theory of reality. (R. Jones, Bull. Am. Phys. Soc., vol. 5, 2011) In a quantum computer the processing (thinking) takes place either in computers in Everett's many worlds or else in the many dimensional Hilbert space. (Depending upon your interpretation of QM.) If our brains were quantum computers then there might be a world of mind which is distinct from the physical world that our bodies occupy. (4 space) This is much like the spirit-body dualism of Descartes and others. My own view is that thought and mind are classical phenomena (see www.robert-w-jones.com, philosopher, theory of thought and mind) but it would be interesting to run an artificial intelligence like my A.S.A. H. on a quantum computer. Might this produce, for the first time, a hypermind in its own universe? [Preview Abstract] |
|
G1.00288: P$\ne $NP Millenium-Problem(MP) TRIVIAL Physics Proof Via NATURAL TRUMPS Artificial-``Intelligence'' Via: Euclid Geometry, Plato Forms, Aristotle Square-of-Opposition, Menger Dimension-Theory Connections!!! NO Computational-Complexity(CC)/ANYthing!!!: Geometry!!! London Clay, Karl Menger, Gian-Carlo Rota, Alexandria Euclid, Edward Siegel P $\ne $NP MP proof is by computer-"science"/SEANCE(!!!)(CS) computational-"intelligence" lingo jargonial-obfuscation(JO) NATURAL-Intelligence(NI) DISambiguation! CS P$=$(?)$=$NP MEANS (Deterministic)\textbullet (PC)$=$ (?)$=$(Non-D)\textbullet (PC) i.e. D\textbullet (P)$=$(?)$=$ N\textbullet (P). For inclusion(equality) vs. exclusion (inequality) irrelevant (P) simply cancels!!! (Equally any/all other CCs IF both sides identical). Crucial question left: (D)$=$(?)$=$(ND), i.e. D $=$(?)$=$ N. Algorithmics[Sipser[Intro. Thy.Comp.(`97)-p.49;Fig.1.15!!!]]: Deterministic (D) serial VS. Non-deterministic (N) NON-serial, branch fork forms triangles, its vertices a plane. Menger Dimension-Theory: Dimensionality: D serial is dim(D)$=$1(definition), VS. N non-serial is dim(N)$=$[2(branching;fork;triangle;plane)$+$E(probabilistic)]\textgreater 2(\textgreater \textgreater \textgreater )$\ne $1! Hence by (Euclid[\textasciitilde -300 BCE]) simple geometry, dim(D)$=$1 $\ne $dim(N)\textgreater 2, Left-to-Right INclusion VS. Right-to-Left EXclusion. Thus TRIVIALLY P $\ne $ NP!!! QED FIN, i.e. D$\ne $N by \textasciitilde -300 BCE GEOMETRY, just ``a tad'' before CS CC JO!!! Harder proofs, but still amenable to NI analysis, are any combinations with DISsimilar CCs, especially LHS combining D with low CC and/or RHS combining N with different CCs: EXP and/or LOG! MUCH HARDER but still amenable to CC NI are: CROSS-MIXTURES: P$=$(?)$=$N\textbullet LOG, EXP$=$(?)$=$N\textbullet P, EXP$=$(?)$=$N\textbullet LOG,... [Preview Abstract] |
|
G1.00289: A Practical Experiment to Obtain Either Which-Way or Interference Photon Distributions at a Distance Using Delayed Choice and Without Correlating Measurement Results on Entangled Photons Douglas Snyder For a pair of entangled signal-idler photons, one may ``lose'' the idler photon (that provides which-way information to the entangled signal photon) in many other photons with similar characteristics to the idler photon before the signal photon is detected, thereby losing the which-way information supplied to the signal photon and eliminating the entanglement. The experiment allows for a delayed choice on the idler photons (whether or not to lose the idler photon before the signal photon is detected) to determine the distribution of distant signal photons (either overall which-way or overall interference) without making correlations between signal and idler photon detections. When the idler photon is lost, it is lost in an optical microcavity filled with photons in the same mode as the idler photon. The experiment could provide the basis for a useful quantum communications device. It might be possible to use a micropost coated with a material such as Vantablack in place of the optical microcavity. [Preview Abstract] |
|
G1.00290: Quantum Entanglement in a two-atom two photon system Samina Masood We study the quantum entanglement in a two atom and two photon system and show that the quantum entanglement can be used in quantum computation to develop more efficient systems. [Preview Abstract] |
|
G1.00291: Quantum Knowledge Diagrams-2, Principles and Application Douglas Snyder The principles behind quantum knowledge can be extracted from the specific empirical implementations so that pictorial elements can be developed representing fundamental concepts of quantum knowledge. With these elements, one can represent quantum knowledge principles underlying specific empirical implementations more simply and in a way that allows for a more direct comparison of quantum knowledge principles underlying various specific empirical implementations. These representations are quantum knowledge diagrams. Basic diagram elements include: 1) a which-way process; 2) a non-which-way process (showing interference); 3) availability of the which-way or non which-way information to the environment, generally through detection, or lack of such availability; 4) particles; 5) entanglement, or lack thereof, of 2 or more particles; 6) delayed choice. Quantum knowledge principles underlying specific empirical implementations are developed and diagrammed. [Preview Abstract] |
|
G1.00292: MATTER AT EXTREME CONDITIONS |
|
G1.00293: New impact sensitivity test of liquid explosives. . Andrei Tiutiaev, Valeri Trebunskih The sensitivity of liquid explosive in the presence of gas bubbles increases many times as compared with the liquid without gas bubbles. Local hot spot in this case formed as a result of compression and heating of the gas inside the bubbles. If we consider that in the liquid as a result of convection, wave motion, shock, etc. gas bubbles are easily generated, the need to develop a method for determining sensitivity of liquid explosives to impact and a detailed study of the ignition explosives with bubbles is obvious. On a mathematical model of a single steam bubbles in the fluid theoretically considered the process of initiating explosive liquid systems to impact. For the experimental investigation, the well-known K-44 -II with the metal cap were used. Instead of the metal cap in the standard method in this paper there was polyurethane foam cylindrical container with LHE, which is easily deforms by impact. A large number of tests with different liquid explosives were made. It was found that the test LHE to impact with polyurethane foam to a large extent reflect the real mechanical sensitivity due to the small loss of impact energy on the deformation of the metal cap, as well as the best differentiation LHE sensitivity due to the higher resolution method . [Preview Abstract] |
|
G1.00294: \textbf{Ultrafast laser diagnostics for understanding hot spot initiation in energetic materials} Ian Kohl, Darcie Farrow, Sean Kearney, Robert Knepper, Jeffrey Kay Ultrafast laser diagnostics have opened new pathways for investigation of shock physics and initiation of energetic materials. Recent work (Bolme LANL/Armstrong LLNL) has demonstrated that short laser pulses can be utilized for direct laser drive and coupled with imaging, spectroscopic, and interferometric tools for studies of dynamic shock loading on picosecond time scales. At Sandia, we are developing diagnostic platforms which extend this earlier work by combining Ultrafast Shock Interferometry (USI) (Armstrong LLNL) and femtosecond transient absorption spectroscopy for tabletop measurement of Hugoniot/Equation-of-state data and characterization of shock structure in heterogeneous materials with micron spatial resolution while probing shock-induced changes in the electronic structure, which have been proposed to drive rapid chemical changes behind the shock front. We will describe the details of our measurement systems, as well as recent progress toward new laser-diagnostic data on inert/explosive thin-film samples. [Preview Abstract] |
|
G1.00295: High Pressure Structures and Equations of State of HIO3 and HI3O8 Joseph Zaug, Elissaios Stavrou, Brian Little, Sorin Bastea, Jonathan Crowhurst Knowledge of high-pressure thermodynamic properties of iodine containing oxides and acids is important toward improving the accuracy of semi-empirical predictions of extreme condition explosive and combustive chemistry of iodine containing formulations. Here we report on the synthesis of explosive chemical products HIO3 and HI3O8 and on the structures and isotropic equations of state up to 35 and 45 GPa respectively. EOS model parameters are provided including parametrized exponential-6 interatomic potential values used to conduct thermochemical calculations of iodine containing reactants. [Preview Abstract] |
|
G1.00296: Anomalous bond length behavior and a new solid phase of bromine under pressure Min Wu, John Tse, Yuanming Pan The behavior of diatomic molecular solids under pressure have attracted great interests and been extensively studied. Under ambient pressure, the structure of bromine is known to be a molecular phase (phase I). With increasing pressure, it transforms into an incommensurate phase (phase V) before eventually to a monoatomic phase (phase II). However, between phases I and V, the interatomic distance was found to first increase with pressure and then decrease abruptly. This anomalous bond length behavior is accompanied by the splitting of the Raman bands. These phenomena have not been resolved. Here we suggest a new solid phase that explains the Raman spectra. Furthermore, the anomalous bond length behavior is found to be the result of subtle second neighbor intermolecular interactions and is an intrinsic property of bromine in molecular phases. [Preview Abstract] |
|
G1.00297: Propagation of light in a Dense Medium. Samina Masood, Iram Saleem Propagation of light is studied in a very dense system. Renormalization scheme of QED is used to understand the propagation of light in a hot and dense medium. We consider a medium of a very large chemical potential with relatively small temperature. The generalized results of vacuum polarization of photon in a hot and dense medium is used to study the behavior of light in such a system. Our hypothetical system corresponds to a heat bath of electrons at an equilibrium temperature and the density of electrons is larger as compared to the temperature of the medium. Such type of systems have previously been identified as classical systems because the chemical potential is large enough to dominate temperature. [Preview Abstract] |
|
G1.00298: High Pressure synchrotron XRD and Raman studies of Ho$_{\mathrm{0.5}}$Y$_{\mathrm{1.5}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7}}$. Melanie White, Ravhi Kumar, Jason Baker, Brian Light Pyrochlore oxides are of interest for their spin-frustrated systems and their proposed use in high-level nuclear waste management. We sought to examine the structural stability of these materials under extreme conditions in order to help determine their viability for applications. A compression and decompression study of Ho$_{\mathrm{0.5}}$Y$_{\mathrm{1.5}}$Ti$_{\mathrm{2}}$O$_{\mathrm{7\thinspace }}$ was done in approximately 5 GPa intervals to above 55 GPa with both synchrotron powder x-ray diffraction at the Argonne National Laboratory Advanced Photon Source, and Raman spectroscopy at the University of Nevada - Las Vegas High Pressure Science and Engineering Center (HiPSEC). In both studies, pressurization of sample was achieved using a symmetric-style diamond anvil cell (DAC). The results are compared with the high pressure behavior of other rare earth titanates. A reversible phase transition is observed between 45 and 49 GPa in both studies. The x-ray diffraction patterns are analyzed in order to identify the crystal structure of the new phase. Vibrational modes are assigned to the Raman spectra and tracked as a function of pressure. Our poster will discuss the results in detail. [Preview Abstract] |
|
G1.00299: PHYSICS OF CLIMATE |
|
G1.00300: A new model of the electron temperature in the topside ionosphere Zahra Panahi Estarkhi, Ali Bakhshayeshi hra Panahi Estarkhi, Ali Bakhshayeshi \textit{Young Researchers and Elite club, Mashhad Branch, Islamic Azad University, Mashhad, Iran} \textit{Department of physics, Mashhad Branch, Islamic Azad University, Mashhad, Iran} -abstract- By using empirical models of electron density in the ionosphere, height equations as a function of electron density from $\alpha $-Chapman, Epstein and exponential functions have been achieved. Plotting the achieved height equations, the one derived from Epstein function has been known as the best fit for height. Locating height derived from Epstein function in an empirical function for electron temperature, a new empirical model for electron temperature as a function of electron density has been achieved and applied to obtain directly the electron temperature for every electron density in the topside ionosphere. Latitudinal and seasonal variations for Te have been plotted in the heights above hmF2 to 1000km to compare the new Te model with the previous empirical model and the measured data from the ISIS database. The results are compared and the possible reasons for difference and similarities are also discussed. [Preview Abstract] |
|
G1.00301: Algorithms for ice halo detection in all-sky images Michelle King, Morton Greenslit, Sylke Boyd The effect of cirrus clouds on the radiation budget of the atmosphere depends not only on optical depth and frequency of occurrence, but also on the composition of the clouds. Ice halo phenomena signal the presence of hexagonal crystal habits. Long-term observations on frequency, duration, and type of halo appearances can give ground-based insight into the behavior of cirrus composition. We are capturing images of the entire sky at 30 second intervals using an all-sky camera. We have created a program that analyzes these images for the presence of halos. The algorithm removes the lens distortion, excludes low-level clouds from further analysis, measures the radial RGB color channel intensity, and uses this radial intensity to assess for ice halo presence. We will present our algorithms for image analysis, including removing the lens distortion and low-level clouds, as well as the algorithm to assign a halo probability. We will also present our observation results for the year 2015. [Preview Abstract] |
|
G1.00302: Construction of a low-cost LIDAR for cirrus cloud observations Brittney Ferrian, Kevin J Boyd, Sylke Boyd Our physical understanding of the Earth's climate is critically linked to our quantitative understanding of cloud coverage and behavior. In particular, cirrus clouds are pivotal players in the radiation balance of the Earth. We have taken a route to capture the characteristics of cirrus clouds using an all-sky camera, and analyzing halo phenomena. That gives us a 2d distribution of the cloud. Neither altitude nor optical thickness can be determined from photographs alone. We are interested in combining altitude and thickness information with the brightness information gathered in images. That requires that the Lidar measures are taken at the time at which a halo photograph is taken. A simple LIDAR instrument with cheap and readily available components is being constructed for this purpose. We will present the layout of the instrument design, challenges in construction and weather-proofing and preliminary measurement results. [Preview Abstract] |
|
G1.00303: Measurement of Water Vapor in the Lower Troposphere Using LIDAR Francis Mensah, Peter Instiful, Arthur Thorpe Water vapor is an important atmospheric variable which plays a key role in air quality, global warming, and climate change. It is known as a highly variable atmospheric constituent. Moreover, water vapor remains one of the most poorly characterized meteorological parameters. For example, water vapor measurements have proven to be difficult below 500 m in the lower troposphere. The overlap which exists between the incident laser beam and the receiver FOV is a factor affecting the lidar observation in the near field range. Because of its particular importance in tropospheric processes and the extraordinary ability of Raman Lidar through the SOLEX system$^{\, }$to sense accurately its high temporal and spatial structure in the atmosphere, we present here some particular details about the use of Raman Lidar SOLEX system to measure water vapor at lower atmosphere at several fixed ranges. A comparison is made between data obtained from the laser system and the ones obtained from calibrated temperature and relative humidity's sensors at the same location. [Preview Abstract] |
|
G1.00304: Effect of Seasonal Variation of Anomalous Condition on Radio Propagation in Nigeria Israel Emmanuel, Babatunde Adeyemi, Emmanuel Ogolo, Adekunle Adediji Daily variation of effective earth radius factor and seasonal variation of refractivity gradients from surface to around 1000 m above ground level in the tropospheric layer are presented based on observation from the meteorological data obtain from ECMWF database. Thirty four years (1979 -2014) of data from surface and profile of Era Interim of the temperature and relative humidity are used to determine the surface anomalous propagation over some selected location I Nigeria. Estimation of anomalous propagation are observed for onset and peak of rainy and dry seasons. The occurrence of anomalous strongly depends on the local time and synoptic weather conditions which have an appreciable on the refractivity vertical profile, especially the seasonal north -- south movement of inter tropical Convergence Zone (ITCD) which provide wet and dry seasonal variations of anomalous were also determined. Spatial distribution of refractivity gradient for both wet and dry seasons are also obtained. The highest occurrence of duct were noticed in the night and morning (00:00 UTC and 06:00UTC) across the country though it was low in the northern part of the country, while low or no occurrence of duct were observed in the afternoon and evening (12:00 UTC and 18:00 UTC). Also percentage occurrence of duct were also high and low during the wet and dry seasons respectively. [Preview Abstract] |
|
G1.00305: INSTRUMENTATION AND MEASUREMENTS |
|
G1.00306: Charge Content In Nanometer Rings from Atomic Force Microscope (AFM) Traces F. Zypman, S. Eppell, M. Feinstein, Y. Fried, D. Lazarev, C. Metzger The last few years have seen a growing interest in identifying charge content in small structures such as graphene ribbons and aromatic biorings. More generally it is believed that charge content in proteins holds the key to the ultimate understanding of biological self-assembly. Here we describe a model system, a charged ring inside liquid probed by an AFM tip, and show how the charge content and the relative size of the ring with respect to the tip affect the measured force. More importantly, we explain how to measure the charge from the AFM experimental data [1]. The process involves the modeling of the dynamics of the tip-cantilever sensor under the influence of the charged sample, but also of ambient hydrodynamic forces, electrostatic interactions that appear due to charge induction in the tip and electrolytic screening. Of particular relevance is the possibility of our approach to treat analytically the size of ions. This is relevant when the tip-sample distance becomes sub-nanometric, and the more common description via Poisson-Boltzmann equation breaks down. [1] Mehlman and F.R. Zypman, Scanning Probe Microscope Force Reconstruction Algorithm via Time-Domain Analysis of Cantilever Bending Motion, J. Adv. Microsc. Res. 9, 268-274 (2014). [Preview Abstract] |
|
G1.00307: Analyzing qPlus sensor assemblies for optimized simultaneous scanning tunneling and non-contact atomic force microscopy operation using finite element method Omur Dagdeviren, Udo Schwarz Scanning tunneling microscopy (STM) and non-contact atomic force microscopy (NC-AFM) are powerful methods that can not only visualize a surface's atomic structure, but also probe its electronic and chemical properties with picoampere, piconewton, and picometer resolution. Quartz tuning forks in qPlus configuration that have a metallic probe tip attached to the end of the free prong have gained considerable popularity in recent years for simultaneous high-resolution STM/NC-AFM experiments. Due to the small size of the tuning forks and the complexity of the sensor architecture, it is, however, not intuitive to judge how variations in the execution of the individual assembly steps affect the completed sensor's performance. In this presentation, we analyze the influence of each assembly step on the sensor's final performance using finite element method. The results show that when the tunneling current is collected using a separate wire, the exact realization of this wire connection has major effect on the sensor's performance. In addition, we show how other design choices such as the exact amount of epoxy used at key interfaces affects parameters such as spring constant, $Q$-factor, and resonance frequency. [Preview Abstract] |
|
G1.00308: Angle-Resolved Light-Matter Interaction in Anisotropic Layered Black Phosphorus Shengxi Huang, Xi Ling, Eddwi Hasdeo, Liangbo Liang, William Parkin, Yuki Tatsumi, Ahmad Nugraha, Alexander Puretzky, Paul Das, Bobby Sumpter, David Geohegan, Jing Kong, Riichiro Saito, Marija Drndic, Vincent Meunier, Mildred Dresselhaus Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride and tin selenide, stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to-date, as shown by a number of inconsistencies in the recent literature. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron-photon and electron-phonon interactions in BP. We highlight, both experimentally and theoretically, a non-trivial dependence between anisotropies and flake thickness, photon and phonon energies. We show that the anisotropic optical absorption is a reliable and simple way to identify the crystalline orientation of BP, which cannot be determined from Raman spectroscopy without the explicit consideration of excitation wavelength and flake thickness. [Preview Abstract] |
|
G1.00309: Open-Source Programming for Automated Generation of Graphene Raman Spectral Maps P. Vendola, M. Blades, W. Pierre, S. Jedlicka, S.V. Rotkin Raman microscopy is a useful tool for studying the structural characteristics of graphene deposited onto substrates. However, extracting useful information from the Raman spectra requires data processing and 2D map generation. An existing home-built confocal Raman microscope was optimized for graphene samples and programmed to automatically generate Raman spectral maps across a specified area. In particular, an open source data collection scheme was generated to allow the efficient collection and analysis of the Raman spectral data for future use. [Preview Abstract] |
|
G1.00310: Effects of magnetic field and pressure in magnetoelastic stress reconfigurable thin film resonators for magnetic field sensing Peter Finkel, Margo Staruch The magnetic response of microdevices is significantly enhanced at structural resonance allowing for improved sensitivity and signal-to-noise ratio. The magnetic field resolution of these devices can be further improved when operating in vacuum due to an increase in mechanical quality factor. In this work, free-standing CoFe thin film doubly clamped stress reconfigurable resonators were investigated as a function of magnetic field and pressure. A large uniaxial anisotropy resulting from residual uniaxial tensile stress was revealed from magnetic hysteresis loops with the easy magnetization axis aligned along the length of the beams. The quality factor of the driven resonator beams under vacuum is increased by 30 times which is expected to lead to improved signal to noise ratio, combined with a predicted reduction in the intrinsic magnetic noise by a factor of 6 potentially reaching as low as \textasciitilde 25 pT/$\surd $Hz at 1 Torr. Stress reconfigurable sensors operating under vacuum could thus further improve the limit of detection and advance development of magnetic field sensing technology. [Preview Abstract] |
(Author Not Attending)
|
G1.00311: Fabrication and performance analysis of a simple, cost-effective copper oxide / zinc oxide semiconductors composite for gas sensing Rafael Velazquez, Manuel Rivera, Eric Li, Peter Feng We report on our studies of composite zinc oxide semiconductor (COS) nanoparticles as sensing materials for the development of high-performance gas sensors. The average diameter of the nanoparticles is 40 nm. The basic electrical properties of sensing materials have been measured. The morphologic surface and crystalline structures of COS are characterized by using scanning electron microscopy (SEM) and Raman scattering spectroscopy, respectively. By using synthesized COS of CuO-ZnO materials, prototypic highly sensitive gas sensors have been designed, fabricated and tested. Important stability and repeatability features have been obtained. The sensitivities of the COS based sensors to methane and hydrogen gases as a function of time and the gas concentrations have been determined. Various sensing parameters including the sensitivity, response time, recovery time, and thermal effect on the gas sensor performance have also been investigated in order to reveal the sensing ability. Analyses of experimental data indicate that the obtained response and recovery are almost 10 times faster than conventional sensors constructed solely from one material. [Preview Abstract] |
|
G1.00312: Microfabrication of Arrays of Superconducting Transition Edge Sensors for CMB Measurements Chrystian Posada, Junjia Ding, Amy Bender, Trupti Khaire, Sergi Lendinez, Samuel Ciocys, Gensheng Wang, Volodymyr Yefremenko, Steve Padin, John Carlstrom, Clarence Chang, Valentine Novosad The cosmic microwave background (CMB) provides a unique window for exploring fundamental physics. Increasing the sensitivity of CMB experiments requires fabricating focal planes with orders of magnitude more detectors than current instruments. This work presents the procedures used at Argonne National Laboratory for the fabrication of large arrays of dual-polarized multichroic detectors for CMB measurements. The detectors are composed of a broad-band sinuous antenna coupled to a Nb microstrip transmission line. In-line filters define the spectral response, allowing for individual measurement of three band-passes (95 GHz, 150GHz and 220 GHz). A Ti /Au termination resistor is used to couple the mm-wave signal to Ti/Au transition edge sensor (TES) bolometers. There are six bolometers per pixel, for a total of 16,140 detectors in the CMB receiver being fabricated. The monolithic microfabrication of the detector arrays will be presented and discussed in detail. [Preview Abstract] |
|
G1.00313: Measurement of the low energy spectral contribution in coincidence with valence band (VB) energy levels of Ag(100) using VB-VB coincidence spectroscopy R.W. Gladen, P.V. Joglekar, Z.H. Lim, K. Shastry, S.L. Hulbert, A.H. Weiss A set of coincidence measurements were obtained for the study and measurement of the electron contribution arising from the inter-valence band (VB) transitions along with the inelastically scattered VB electron contribution. These Auger-unrelated contributions arise in the Auger spectrum ( Ag 4p NVV) obtained using Auger Photoelectron Coincidence Spectroscopy (APECS). The measured Auger-unrelated contribution can be eliminated from Auger spectrum to obtain the spectrum related to Auger. In our VB-VB coincidence measurement, a photon beam of energy 180eV was used to probe the Ag(100) sample. The coincidence spectrum was obtained using two Cylindrical Mirror Analyzers (CMA's). The scan CMA measured the low energy electron contribution in the energy range 0-70eV in coincidence with VB electrons measured by the fixed CMA. In this talk, we present the data obtained for VB-VB coincidence at the valence band energy of 171eV along with the coincidence measurements in the energy range of 4p core and valence band. [Preview Abstract] |
|
G1.00314: Simulation-based Extraction of Key Material Parameters from Atomic Force Microscopy huseen alsafi, Gray peninngton Models for the atomic force microscopy (AFM) tip and sample interaction contain numerous material parameters that are often poorly known. This is especially true when dealing with novel material systems or when imaging samples that are exposed to complicated interactions with the local environment. In this work we use Monte Carlo methods to extract sample material parameters from the experimental AFM analysis of a test sample. The parameterized theoretical model that we use is based on the Virtual Environment for Dynamic AFM (VEDA) [1]. The extracted material parameters are then compared with the accepted values for our test sample. Using this procedure, we suggest a method that can be used to successfully determine unknown material properties in novel and complicated material systems. [Preview Abstract] |
|
G1.00315: Modeling of the energy resolution of a 1 meter and a 3 meter time of flight positron annihilation induced Auger electron spectrometers. A FAIRCHILD, V CHIRAYATH, R GLADEN, A MCDONALD, Z LIM, M CHRYSLER, A KOYMEN, A WEISS Simion 8.1\textregistered simulations were used to determine the energy resolution of a 1 meter long Time of Flight Positron annihilation induced Auger Electron Spectrometer (TOF-PAES). The spectrometer consists of: 1. a magnetic gradient section used to parallelize the electrons leaving the sample along the beam axis, 2. an electric field free time of flight tube and 3. a detection section with a set of ExB plates that deflect electrons exiting the TOF tube into a Micro-Channel Plate (MCP). Simulations of the time of flight distribution of electrons emitted according to a known secondary electron emission distribution, for various sample biases, were compared to experimental energy calibration peaks and found to be in excellent agreement. The TOF spectra at the highest sample bias was used to determine the timing resolution function describing the timing spread due to the electronics. Simulations were then performed to calculate the energy resolution at various electron energies in order to deconvolute the combined influence of the magnetic field parallelizer, the timing resolution, and the voltage gradient at the ExB plates. The energy resolution of the 1m TOF-PAES was compared to a newly constructed 3 meter long system. The results were used to optimize the geometry and the potentials of the ExB plates for obtaining the best energy resolution. [Preview Abstract] |
|
G1.00316: Spectra of electrons emitted as a result of the sticking and annihilation of low energy positrons to the surfaces of graphene and highly oriented pyrolytic graphite (HOPG) M CHRYSLER, V CHIRAYATH, A MCDONALD, Z LIM, K SHASTRY, R GLADEN, A FAIRCHILD, A KOYMEN, A WEISS Positron annihilation induced Auger electron spectroscopy (PAES) was used to study the positron induced low energy electron spectra from HOPG and a sample composed of 6-8 layers of graphene grown on polycrystalline copper. A low energy (\textasciitilde 2eV) beam of positrons was used to implant positrons into a surface localized state on the graphene and HOPG samples. Measurements of the energy spectra of the positron induced electrons obtained using a TOF spectrometer indicate the presence of an annihilation induced KLL C Auger peak (at \textasciitilde 263 eV) along with a narrow low energy secondary peak due to an Auger mediated positron sticking (AMPS) process. A broad spectral feature was also observed below \textasciitilde 15 eV which we believe may be due to a VVV C Auger transition not previously observed. The energy dependence of the integrated intensity of the AMPS peak was measured for a series of incident positron kinetic energies ranging from \textasciitilde 1.5 eV up to 11 eV from which the binding energy of the surface localized positron state on graphene and HOPG was estimated. The implication of our results regarding the applicability of AMPS and PAES to the study of graphene surfaces and interfaces will be discussed. [Preview Abstract] |
|
G1.00317: Scanning SQUID microscopy in a cryogen-free refrigerator Brian T. Schaefer, David Low, Guenevere E. D. K. Prawiroatmodjo, J. Kevin Nangoi, Jihoon Kim, Katja C. Nowack With helium prices rising and supply becoming increasingly uncertain, it has become attractive to use dry cryostats with cryocoolers rather than liquid helium to reach low temperatures. However, a cryocooler introduces vibrations at the sample stage, making scanning probe experiments more challenging. Here, we report our progress on a superconducting quantum interference device (SQUID) microscope implemented for the first time in a compact, cryogen-free 5 K system. Our microscope is designed to reach submicron spatial resolution and a flux sensitivity of approximately 1 $\mu \Phi_0 /\sqrt{\rm Hz}$, where $\Phi_0$ is the magnetic flux quantum. To enable height feedback while approaching and scanning samples, we mount the SQUID on a quartz tuning fork. Our system promises to meet the capabilities of similar systems implemented in helium cryostats. [Preview Abstract] |
|
G1.00318: Refocusing and high field generation of terahertz radiation in two-color laser filamentation Yungjun Yoo, Donghoon Kuk, Ki-Yong Kim We have demonstrated strong terahertz (THz) field generation by using femtosecond two-color laser mixing in air. In this experiment, we have tested THz energy scaling and refocusing by varying the lens focal length from 200 mm to 1 m. We find that the output THz energy greatly enhances with increasing focal length (or plasma filament length), which is consistent with previous reports. In addition, contrary to our previous concern that long filamentation may yield more THz energy but unfavorably increase the focused spot size, both short and long filamentation provide small spot sizes (35\textasciitilde 50 microns in FWHM). This implies that the peak field 8 MV/cm, previously achieved with a 200 mm focal length, can be greatly enhanced with long filamentation and tight refocusing. In addition, for real-time THz beam profiling, an uncooled microbolometer camera is used with lock-in detection, providing enhanced signal-to-noise ratios at a broad range of THz (1\textasciitilde 40 THz) frequencies. [Preview Abstract] |
|
G1.00319: Generation of scalable terahertz radiation from cylindrically focused laser pulses in air Donghoon Kuk, Yungjun Yoo, Eric Rosenthal, Nihal Jhajj, Howard Milchberg, Ki-Yong Kim We have demonstrated scalable terahertz (THz) generation via cylindrical focusing of two-color laser pulses in air. In this experiment, we have used a terawatt (TW) laser system which can deliver \textgreater 50 mJ, 800 nm, 50 fs pulses at a 10 Hz repetition rate. A 800 nm pulse passing through a nonlinear crystal (BBO) generates its second harmonic pulse (400 nm). Both pulses pass through a cylindrical lens and are focused together to generate a 2-dimensional plasma sheet in air. This yields two diverging THz lobes, characterized by an uncooled microbolometer. This observed radiation angle and pattern is explained by the optical-Cherenkov radiation theory. The diverging THz radiation is re-focused to yield strong THz field strengths (\textgreater 20 MV/cm) at the focus. At laser energy of 40 mJ, cylindrical focusing provides THz energy of \textgreater 30 microjoules, far exceeding the output produced by spherical focusing. This shows that cylindrical focusing can effectively minimize ionization-induced defocusing, previously observed in spherical focusing, and can allow scalable THz generation with relatively high laser energies (\textgreater 20 mJ). [Preview Abstract] |
|
G1.00320: Interaction of high density, thin, gas jets with ultrashort laser pulses at 1 kHz repetition rates Yan Tay, Donghoon Kuk, Howard Milchberg, Ki-Yong Kim We have investigated the interaction of thin (50 \textasciitilde 150 microns), high-density (10$^{19}$ \textasciitilde 10$^{21}$ cm$^{-3})$ gas jets with 30 fs, \textgreater 5 mJ, 800 nm laser pulses at a 1 kHz repetition rate. Capillary tubes with various diameters (50 \textasciitilde 500 microns) are used to produce dense gas jets in continuous flow at high backing pressure (\textasciitilde 1000 psi) and cryogenic temperature (130 K). The gas/plasma density profiles are characterized by optical interferometry, and Rayleigh/Mie scattering is measured to characterize coexisting atomic clusters. Our result shows a peak plasma density of 10$^{21}$ cm$^{-3}$ near the nozzle orifice, approaching the critical plasma density at 800 nm laser wavelength. This high density plasma efficiently produces X-rays and terahertz radiation, as well as energetic electrons and ions at high-repetition-rates (kHz), without generating unwanted debris as in solid targets. [Preview Abstract] |
|
G1.00321: Ultrasmall Angle X-ray Scattering (USAXS) and Wide Angle X-ray Scattering (WAXS) Studies on the Complex Metal Hydride NaAlH4 Tabbetha Dobbins, Christopher Bennett, James Torres, Jan Ilavsky This research seeks to understand the role of ScCl , ZrCl , and VCl catalysts in NaAlH. We have examined these hydrides at multiple length scales using an X-ray scattering instrument which is capable of measuring scattering wave vector, Q, of 0.0001{\AA} to 6.0 {\AA} . The ultrasmall angle X-ray scattering (USAXS) instrument sector 9ID-D of the Advanced Photon Source (APS) simultaneously collects using USAXS, SAXS, and WAXS detectors. Studies were performed during in-situ heating up to 170C (just below the H desorption temperature for uncatalyzed NaAlH ). Results showed that NaAlH has a surface fractal (highly porous) morphology. Isothermal studies performed at 30C, 65C, 100C, 135C, and 170C reveals changes at low Q (Q\textasciitilde 0.001 {\AA} to 0.01 {\AA} ) associated with highly interconnected intraparticle porosity which is suitably described by a power-law slope for a Gaussian polymer chain structure of p\textasciitilde 2. At high scattering wave vector, Q\textasciitilde 0.03 {\AA} , the presence of a pore population which obeys Porod scattering and appears to have a size at 21nm is present. These fine pores increase in their population density as temperature is elevated. The WAXS data reveals thermal expansion to occur, but no solid state phase transformation to the product phase. [Preview Abstract] |
|
G1.00322: Adaptive measurement of spin decoherence time $T_{2}$ Yihao Zhang, Wen Yang Spin decoherence time $T_{2}$ is an important parameter in quantum mechanics. In order to estimate it accurately and efficiently, we propose a scheme for spin decoherence time $T_{2}$ estimation of a single spin using adaptive measurement. While the ordinary scheme of measuring $T_{2}$ yield an estimate precision scales with mean-square error $\sim 1/\sqrt{N}$ ($N$ is the number of measurements). We present some simulated measurement which shows that the adaptive scheme, that is, the time between measurements was depended on the prior measurement results, will give a better scaling than MSE. [Preview Abstract] |
|
G1.00323: Single-shot ultrafast interferometric imaging Daiwei Zhu, Donghoon Kuk, Ki-Yong Kim We have developed a new interferometric method capable of capturing 2-dimensional, time-varying phase and amplitude profiles in a single shot. Most single-shot interferometry provides one-dimensional spatial information as demonstrated in detecting laser-produced transients, phase transition, and plasma generation. By contrast, our new method can provide 2-dimensional spatial information at multiple time delays in a single shot. In this scheme, we analyze the limits of spatial and temporal resolution and have tested the working principle with a computer simulation. This new diagnostic holds a great potential in study ultrafast phenomena occurring on sub-picosecond time scales. [Preview Abstract] |
|
G1.00324: Elastic scattering of Electrons and Positrons by Cadmium Atom*) B. C. Saha, A. K. F. Haque, M. I. Hossain, M. A. Uddin, M. A. R. Patoary, M. Maaza, A. K. Basak The differential, integrated elastic, total and momentum transfer cross sections with Sherman functions for the elastic scattering of electrons and positrons by cadmium atom have been calculated. These calculations are done within the framework of complex electron/positron-atom optical potential and relativistic Dirac partial wave analysis at energies 6.4 to 1000 eV for both electrons and positrons impact. Our results are compared with available experimental and other theoretical cross section values. Details of our findings will be presented at the conference. *) BCSaha is thankful to NNSA for partial support. [Preview Abstract] |
|
G1.00325: \textbf{Low energy C}$^{\mathrm{\mathbf{6+}}}$\textbf{ }$+$\textbf{H}$_{\mathrm{\mathbf{2}}}$\textbf{ scattering: Molecular Close-Coupling Treatment}$^{\mathrm{\mathbf{\ast )}}} \quad \backslash $\textbf{pard}$\backslash $pard Bidhan Saha h $-abstract-$\backslash $pard Collisions of multiply charged ions with molecules are very common in astrophysical plasmas[1]. The ion-molecule calculations are rather more complicated than their atomic counter part. For multi charged ions in X-ray ionized astronomical environments the charge exchange provides a recombination mechanism. To understand this detailed information on the collision cross sections is essential. In highly charged ion-molecule problem the Coulomb term plays an important role; using a pseudo-diatomic technique the colliding system can be approximated by a model potential for the ionic core of H$_{\mathrm{2}}$ with encouraging results [2-5]. Freezing the target, H$_{\mathrm{2}}$ can easily be treated as an atom with appropriate ionization potential (Ip). Our results show good agreement with available experimental findings.$\backslash $pard[1] B. C. Saha, Atomic Structure and Collision process, Narosa Pub. House (2011).2] B. C. Saha et. al., Phys Rev A 44, R1, (1991).3] B C Saha et. al., J. Mol. Structure 487, 11, (1999).4] A. Kumar et al Phys Rev A 59, 1273, (1999).5] B. C. Saha Phys Rev A 56, 2909, (1997).$\backslash $-/abstract-$\backslash $\tex [Preview Abstract] |
|
G1.00326: GENERAL PHYSICS |
|
G1.00327: Absolute Summ Alfred Phillips Jr. Summ means the entirety of the multiverse. It seems clear, from the inflation theories of A. Guth and others, that the creation of many universes is plausible. We argue that Absolute cosmological ideas, not unlike those of I. Newton, may be consistent with dynamic multiverse creations. As suggested in W. Heisenberg's uncertainty principle, and with the Anthropic Principle defended by S. Hawking, et al, human consciousness, buttressed by findings of neuroscience, may have to be considered in our models. Predictability, as A. Einstein realized with Invariants and General Relativity, may be required for new ideas to be part of physics. We present here a two postulate model geared to an Absolute Summ. The seedbed of this work is part of Akhnaton's philosophy (see S. Freud, Moses and Monotheism). Most important, however, is that the structure of human consciousness, manifest in Kenya's Rift Valley 200,000 years ago as Homo sapiens, who were the culmination of the six million year co-creation process of Hominins and Nature in Africa, allows us to do the physics that we do. . [Preview Abstract] |
|
G1.00328: Analysis about the force of electrons revolve around the nucleus Han Yongquan 1, Let's compare the difference of two algorithms: the electrostatic force between protons and electrons, F1 $=$ ke$^{\mathrm{2}}$ / r$^{\mathrm{2}}$, r is the radius of the electron around the nucleus movement -- within 10$^{\mathrm{-10}}$ meters; Electronic movement speed is close to the light- about 10$^{\mathrm{7\thinspace }}$meters per second, the size of the centripetal force F2 $=$ v$^{\mathrm{2}}$m/r. F1 should be approximately equal to F2,calculate the ratio of F1 and F2, F2 / F1 $=$ (v$^{\mathrm{2}}$m/r) (ke$^{\mathrm{2}}$ / r$^{\mathrm{2}})$ / $=$ (10$^{\mathrm{7}}$ * 10$^{\mathrm{7}}$ * 0.91 * 10$^{\mathrm{-30}}$ / r)/(9 * 10$^{\mathrm{9}}$ * 1.6* 10$^{\mathrm{-19}}$*1.6*10$^{\mathrm{-19}}$ / r$^{\mathrm{2}}) \quad =$ 4 x 10$^{\mathrm{3}}$.The calculation shows that not only the electrostatic force and other force. 2, The radius of the electron orbiting around the nucleus named r, F $=$ Ke$^{\mathrm{2}}$ / r$^{\mathrm{2}} \quad =$ 9 x 10$^{\mathrm{9\thinspace }}$x £¨1.6 x 10 $^{\mathrm{-19}}) \quad^{\mathrm{2}}$ / r$^{\mathrm{2\thinspace }}=$ v$^{\mathrm{2}}$m/r, r $=$ 2.5 x 10$^{\mathrm{-14}}$ meters, namely that the radius of hydrogen atom is about 2.5 x 10$^{\mathrm{-14\thinspace }}$meters, that is different with the observed result (10$^{\mathrm{-10}}$ meters).Electrons revolve around the nucleus may faster than 10$^{\mathrm{7\thinspace }}$m/s, can almost reach 10$^{\mathrm{8}}$ meters per second, if the electronic moves by 10$^{\mathrm{8\thinspace }}$meters per second, hydrogen atom radius is approximately 2. 5 x 10 $^{\mathrm{-16}}$ meters, has converged in the interior of the nucleus, it is not possible. Use density to instead of electricity, can solve this problem. Author: hanyongquan TEL: 15611860790 [Preview Abstract] |
|
G1.00329: Nuclear Structure of the Noble Gas Nakyeong Seong Modern physics usually pictures the nuclear structure as about sphere and treats various detailed situation as perturbative, which may be obscured. In addition, the explanation why $^{\mathrm{235}}$U undergoes nuclear fission and $^{\mathrm{238}}$U does not is too difficult and unclear for the people to understand. However, in this paper, we introduce a new approach on the nuclear structure of the noble gas, which simultaneously can explain several phenomena that is obscurely elucidated by modern physics. We consider a 1:1 ratio between protons and neutrons and need the concept of the symmetry of the nuclear structure, because the electron's shell of the noble gas is fully occupied. From these, we can predict the number of neutrons of each noble gas exactly [Preview Abstract] |
|
G1.00330: Negative Casimir entropies Yang Li, Kimball Milton In the last decade, various results on the entropy related to the Casimir interactions between two bodies have been obtained and the striking feature that negative values of Casimir entropy frequently appear. The origin of this effect lies in many factors, such as the dissipation of the materials, the geometry of the configuration and so on. We recently investigated the entropies of one body systems. Although the self-free energy of one body systems are always divergent, the self-entropy could be finite in many cases. These phenomenon may throw more light on thermal dynamical behavior of quantum field systems. [Preview Abstract] |
|
G1.00331: ABSTRACT WITHDRAWN |
|
G1.00332: Number relativity Philip Shin Number relativity 1.Every equation of the relativity is just the way to understand through to solve one question of the math problem. We just add the hypothesis into the number. 2. Sequence of number is the machine physics for software(computer) as the number order is program equation as calculator. 3. When zero is denominator, it is not existing as it is doing something by nothing. So nothing means time as we put zero denominator into time. [Preview Abstract] |
|
G1.00333: Kelvin Absolute Temperature Scale Identified as Length Scale and Related to de Broglie Thermal Wavelength. Siavash Sohrab Thermodynamic equilibrium between matter and radiation leads to de Broglie wavelength $\lambda_{d\beta } =h/m_{\beta } v_{r\beta } $ and frequency $\nu_{d\beta } =k/m_{\beta } v_{r\beta } $ of matter waves and stochastic definitions of Planck $h=h_{k} =m_{k} <\lambda_{rk} >c$ and Boltzmann $k=k_{k} =m_{k} <\nu_{rk} >c$ constants, $\lambda_{rk} \nu_{rk} =c$, that respectively relate to spatial ($\lambda )$ and temporal ($\nu )$ aspects of vacuum fluctuations. Photon mass$m_{k} =\sqrt {hk/c^{3}} $, $amu=\sqrt {hkc} =1/N^{o}$, and universal gas constant $R^{o}=N^{o}k=\sqrt {k/hc} $ result in internal $U_{k} =Nh\nu_{rk} =Nm_{k} c^{2}=3Nm_{k} v_{mpk}^{2} =3NkT$and potential $pV=uN\hat{{v}}/3=N\hat{{u}}/3=NkT$ energy of photon gas in \textit{Casimir vacuum} such that $H=TS=4NkT$. Therefore, Kelvin absolute thermodynamic temperature scale [degree K] is identified as length scale [meter] and related to most probable wavelength and de Broglie thermal wavelength as $T_{\beta } =\lambda_{mp\beta } =\lambda_{d\beta } /3$. Parallel to Wien displacement law obtained from Planck distribution, the displacement law $\lambda_{wS} T=c_{2} /\sqrt 3 $ is obtained from Maxwell$-$Boltzmann distribution of speed of ``photon clusters''. The propagation speeds of sound waves in ideal gas versus light waves in photon gas are described in terms of $v_{r\beta } $ in harmony with perceptions of Huygens. Newton formula for speed of long waves in canals $\sqrt {p/\rho } $ is modified to $\sqrt {gh} =\sqrt {\gamma p/\rho } $ in accordance with adiabatic theory of Laplace. [Preview Abstract] |
|
G1.00334: Time Dilation And Changes Of Material Properties Of An Atom (Body) In Speed Of Near Light Speed Based On The "Substantial Motion"; Theory of Iranian Philosopher, Mulla Sadra Hassan Gholibeigian, Kazem Gholibeigian Iranian Philosopher, Sadr-ol-Moteallehin (1571-1640) said in his famous book, Asfar: "the Universe moves in its entity... and time is its fourth dimension, and time is magnitude of the motion (momentum) of the matter in its entity". In other words, time for each atom is momentum of its involved fundamental particles, [APS March Meeting 2015, abstract #V1.023]. When an atom (body) moves in speed of near light speed, speed of its involved fundamental particles become slow, and consequently the magnitude of its momentum (time) will decrease. On the other hands, when the spin and orbital angular momentum of an atom changed, it means that its properties, mass, strength of its electromagnetic field and its interaction with momentum changed. As a result, each atom (body) which moves in light speed, lower or faster than that, will get a new identity and vice versa. The special relativity can be the special form of this theory. In this way, black holes will be lighter than their involved masses at rest (a paradox with general relativity). Dark matter/energy may be created at first in B.B (Convection Bang) [AGU Fall Meeting 2015, abstract ID: 58425], in more than light speed, so, if we speed protons to more than light speed (in LHC), we may see dark mater/energy in new space-time. [Preview Abstract] |
|
G1.00335: Exploring Baryons for Dark Matter Shantilal Goradia There is on-going research for the detection of WIMP’s based on a speculative idea of supersymmetry, which attempts to unify the fundamental forces of nature, including gravity. The detection of WIMP’s is expected to find a solution to the issue of dark matter. We continue to hold and support our view of the millennium that gravity is not a fundamental force of Nature. We are therefore exploring baryons as the particles to address the issue of dark matter. We poster present our analyses to support our proposal. [Preview Abstract] |
|
G1.00336: Siegel[JMMM 7,312(`\underline {\textit{7}}8)] FIRST EXPERIMENTAL DISCOVERY of Giant-Magnetoresistance Decade Pre ``Fert'' and ``Gruenberg''; ['88 -- `78] $=$ 10-Years $=$ One-Decade Sounds, for Nuclear-Power Na\"{\i}ve ``Panacea'' for Global-Warming/Climate-Chan MasterAce Hoffmann, Edward Siegel Siegel[JMMM 7,312(`\underline {\textit{7}}8); Monju (12/'95) LMFBR PREDICTION!!!] following: Wigner[JAP 17,857(`46)]-(Alvin)Weinberg(ANL/ORNL/ANS)-(Sidney)Siegel(ANL/ORNL/ANS)-Seitz-Overhauser-Rollnick-Pollard-Lofaro-Markey-Pringle[Nuclear-Power;From Physics to Politics(`79)] FIRST EXPERIMENTAL DISCOVERY [Siegel\textless \textless \textless "Fert"-"Gruenberg":2007-Physics-Nobel/2006:-Wolf/Japan-prizes:[`\underline {8}8 --`\underline {\textit{7}}8]$=$\underline {\textit{10}}-years $=$1-decade precedence!!!] of granular giant-magnetoresistance(GMR) [Google: ``EDWARD SIEGEL GIANT-MAGNETORESISTANCE ICMAO 1977 FLICKER'']; [Google: ``Ana Mayo If~\underline {\textit{LEAKS~}}`Could' KILL'']; in austenitic/FCC Ni/Fe-based (so MIScalled)"super"alloy-182/82 transition-welds GENERIC ENDEMIC EXTANT detrimental (SYNONYMS): Wigner's-disease/Ostwald-ripening/spinodal-decompositio/OVERageing-EMBRITTLEMENT/THERMAL-leading-to-mechanical (TLTM)-INstability/``sensitization'' in: nuclear-reactors/spent-fuel dry-casks/refineries/jet/missile/rocket-engines/\textellipsis SOUNDS A DIRE WARNING FOR NAIVE Hansen-Sommerville-Holdren-DOE-NRC-OSTP-WNA-NEI-AIP-APS-\textellipsis calls/media-hype/P.R./spin-doctoring for carbon-``free'' nuclear-power as a SUPPOSED ``panacea'' for climate-change/global-warming: ``TRUST BUT VERIFY!!!'' ; a VERY LOUD CAVEAT EMPTOR!!! [Preview Abstract] |
|
G1.00337: History of ``NANO''-Scale VERY EARLY Solid-State (and Liquid-State) Physics/Chemistry/Metallurgy/ Ceramics; Interstitial-Alloys Carbides/Nitrides/Borides/\textellipsis Powders and Cermets, Rock Shocks, \textellipsis Colin Maiden, Edward Siegel History of ``NANO'': Siegel-Matsubara-Vest-Gregson[Mtls. Sci. and Eng. 8, 6, 323(`\underline {\textit{71}}); Physica Status Solidi (a)11,45(`\underline {\textit{72}})] VERY EARLY carbides/nitrides/borides powders/cermets solid-state physics/chemistry/metallurgy/ ceramics FIRST-EVER EXPERIMENTAL~NANO-physics/chemistry[1968 -\textgreater Physica Status Solidi (a)11,45(`\underline {\textit{72}}); and EARLY NANO-``physics''/NANO-``chemistry'' THEORY(after: Kubo(`62)-Matsubara(`60s-`70s)-Fulde (`65); [ref.: Sugano[\underline {Microcluster-Physics}, Springer('82; `98)]] Siegel [(`70-`73) ---\textgreater Statphys-13, The Technion, Haifa(1977)-C. Kuper and I, Reiss editors, in Annals Israel Academy of Sciences, volume 2(1978); International Conference on Lattice-Dynamics, Paris(`77)-M. Balkanski editor, Flammarion(`78); International Conference on Magnetic Alloys and Oxides(``ICMAO''), The Technion, Haifa(`77)-A. Hirsh and G. Barnea editors, in Journal of Magnetism and Magnetic Materials (JMMM 7, 312) (1978)\textbraceleft where Siegel FIRST EXPERIMENTAL DISCOVERY of granular-giant-magnetoresistance(GMR)[JMMM 7, 312('78)] and FIRST THEORETICAL PREDICTION of colossal-magnetoresistance(CMR)[JMMM 7, 338('78)]\textbraceright ; Semiconductors and Insulators 5: 39,47,62(`79)$=$THREE-contiguous-papers!!!; Scripta Metallurgica 13, 913(`79)], AIP Shock-Physics Meetings: Chicago(`11); Seattle(`13); Tampa(`15); \textellipsis [Preview Abstract] |
|
G1.00338: Implications of the general constraints for single-qubit quantum process tomography Ramesh Bhandari, Nicholas Peters We revisit the general constraints of single qubit quantum process tomography and derive simplified forms in the Pauli basis. These forms give insight into the structure of the process matrix, which we examine in light of several examples. Specifically, we study some qubit leakage error models and show how different error models are manifest in the process matrix. [Preview Abstract] |
|
G1.00339: Optical determination of MoSe$_{\mathrm{2}}$ layer number Xian Zhang, James Hone We mechanically exfoliate mono- and few-layers of molybdenum diselenide. The exact number of layers is determined by atomic force microscopy, high-resolution Raman spectroscopy, and photoluminescence. We have quantitatively summarized the relation between Raman A$_{\mathrm{1g}}$ mode positions and the layer numbers, from both 532nm wavelength and 633nm wavelength Raman lasers. The spectrum analysis is based on 1-4 layer MoSe$_{\mathrm{2}}$ flakes. These observations provide useful information for the future opto-electronic devices based on these materials. [Preview Abstract] |
|
G1.00340: Flexible low-power RF nanoelectronics in the GHz regime using CVD MoS2 Maruthi Yogeesh Two-dimensional (2D) materials have attracted substantial interest for flexible nanoelectronics due to the overall device mechanical flexibility and thickness scalability for high mechanical performance and low operating power. In this work, we demonstrate the first MoS2 RF transistors on flexible substrates based on CVD-grown monolayers, featuring record GHz cutoff frequency (5.6 GHz) and saturation velocity (\textasciitilde 1.8\texttimes 106 cm/s), which is significantly superior to contemporary organic and metal oxide thin-film transistors. Furthermore, multicycle three-point bending results demonstrated the electrical robustness of our flexible MoS2 transistors after 10,000 cycles of mechanical bending. Additionally, basic RF communication circuit blocks such as amplifier, mixer and wireless AM receiver have been demonstrated. These collective results indicate that MoS2 is an ideal advanced semiconducting material for low-power, RF devices for large-area flexible nanoelectronics and smart nanosystems owing to its unique combination of large bandgap, high saturation velocity and high mechanical strength. [Preview Abstract] |
|
G1.00341: Experimental Greenberger-Horne-Zeilinger type six-photon quantum nonlocality Chao Zhang, Yun-Feng Huang, Zhao Wang, Bi-Heng Liu, Chuan-Feng Li, Guang-Can Guo Quantum nonlocality gives us deeper insight into quantum physics. In addition, quantum nonlocality has been further recognized as an essential resource for device-independent quantum information processing in recent years. Most experiments of nonlocality are performed using a photonic system. However, until mow, photonic experiments of nonlocality have involved at most four photons. Here, for the first time, we experimentally demonstrate the six-photon quantum nonlocality in an all-versus-nothing manner based on a high-fidelity (88.4{\%}) six-photon Greenberger-Horne-Zeilinger (GHZ) state. Our experiment pushes multi-photon nonlocality studies forward to the six-photon region and might provide a larger photonic system for device-independent quantum information protocols. [Preview Abstract] |
|
G1.00342: Theoretical studies of graphene nanoribbon quantum dot qubits Chih-Chieh Chen, Yia-Chung Chang Graphene nanoribbon quantum dot qubits have been proposed as promising candidates for quantum computing applications to overcome the spin-decoherence problems associated with typical semiconductor (e.g., GaAs) quantum dot qubits. We perform theoretical studies of the electronic structures of graphene nanoribbon quantum dots by solving the Dirac equation with appropriate boundary conditions. We then evaluate the exchange splitting based on an unrestricted Hartree-Fock method for the Dirac particles. The electronic wave function and long-range exchange coupling due to the Klein tunneling and the Coulomb interaction are calculated for various gate configurations. It is found that the exchange coupling between qubits can be significantly enhanced by the Klein tunneling effect. The implications of our results for practical qubit construction and operation are discussed. [Preview Abstract] |
|
G1.00343: InAs Quantum Dots embedded in GaAs: Properties from Basic Electrical Measurements Azzouz Sellai, Abdelmadjid Mesli C-V and I-V data from a GaAs Schottky diode in which InAs quantum dots (QDs) were embedded are analyzed. The capacitance due to QDs is fitted with an analytical equation that takes into account Gaussian broadening of sub-band levels and contribution of the wetting layer. The voltage range over which the excess capacitance extends is used to estimate the number of charges contained in the QDs. The energy levels of electrons, entirely confined in the QDs, are computed based on a model in which InAs dots are considered of conical shapes and where the effective mass is taken as both position- and energy-dependent. To reconcile the computed energy values with those from the C-V fits, one has to consider a confinement potential other than the potential due to the GaAs/InAs band discontinuity. I-V data could be analyzed using a model that combines field and thermionic emission processes with two distinct behaviors depending on the temperature and bias. Deviations occur at temperatures above 200 K and voltages above 0.4 V. In comparison with the structure with only the wetting layer, the structure with QDs exhibits an excess current in the low-bias forward regime, an indication of contributions from tunneling electrons. [Preview Abstract] |
|
G1.00344: Effect of the In by Bi substitution in the Sm$_{\mathrm{2}}$InTaO$_{\mathrm{7}}$ system for the photocatalytic splitting of water Pablo de la Mora, Melissa Mendez Galvan, Gustavo Tavizon, Juan Ramirez de Arellano Tantalum oxide-based photocatalysts with octahedrally coordinated d$^{\mathrm{10}}$ configuration, represent promising semiconductor systems to develop photocatalysts with visible-light response in the photochemical splitting of water. Several Indium oxide-based compounds have shown acceptable activity in water photolysis. Recently, the pyrochlore Sm$_{\mathrm{2}}$InTaO$_{\mathrm{7}}$ (a 4f-d$^{\mathrm{10}}$-d$^{\mathrm{0}}$ system) was reported as a visible-light photocatalyst for water splitting. In the present work, by solid state reaction, we have obtained and structurally characterized compounds of the Sm$_{\mathrm{2}}$In$_{\mathrm{1-x}}$Bi$_{\mathrm{x}}$TaO$_{\mathrm{7\thinspace }}$system. In these systems we have found that the optical band gap value depends on the Bi content; this value is 2.7, 2.52 and 2,1eV for x$=$0, 0.15 and 0.30 respectively. The specific surface area values we have found are typical of solid state reaction products, 0.5-1.2 m$^{\mathrm{2}}$/g. To understand the effect of the In substitution by Bi, the compounds were studied with first principles calculations using the WIEN2k package and the gap was evaluated using the mBJ potential [Preview Abstract] |
|
G1.00345: Motion of Ferrofluid Droplets Under Oscillating Magnetic Field Yu Gu, Huiyanangel Chow, Karl Morris Ferrofluids are stable, colloidal suspensions of single-domain ferromagnetic particles of nanometer size. Because of their good sealing properties and ease of actuation, ferrofluids are ideal for applications in Lab-On-Chip, or micro-total analysis systems ($\mu $TAS). In particular, because of their changing viscosity and surface properties under magnetic fields, as well as previously reported nonlinear behavior in bulk volumes, understanding the periodic movement of ferrofluid droplets for applications in pumping, valving and switching is important. We characterize the movement of ferrofluid droplets with volumes from 80 nL to 200 nL under oscillating magnetic fields in the frequency range 1Hz to 100Hz. Oil-based ferrofluid droplets are placed in circular cross-sectional capillaries and motion is recorded using a high-speed camera, then distilled using computer-assisted image analysis. Kinematics variables such as the position and velocity of the droplets' centers of mass are observed. Nonlinear behaviors in droplet shape and travel distance per cycle of actuation are also presented. [Preview Abstract] |
|
G1.00346: Electronic Transport and Spatial/Temporal Photocurrent in Monolayer Molybdenum Disulfide Grown by CVD. Zhengfeng Yang, Roberto Grassi, Marcus Freitag, Yi-Hsien Lee, Tony Low, Wenjuan Zhu We systematically investigate the electronic transport in transistors/Hall-bar devices and spatial/temporal photocurrent in photodetectors based on monolayer MoS$_{\mathrm{2}}$ grown by CVD. We found that the maximum photocurrent occurs when laser spot is close to the metal/MoS$_{\mathrm{2}}$ contact and is tunable by the applied drain voltage, which can be explained by the modulation of the local electric field at the Schottky barrier, consistent with predictions from our quantum transport simulation. We observed that the maximum photocurrent at drain contact is much larger than the one at source contact, and the DC currents show rectifying behavior. These phenomena can be explained by the different Schottky barrier heights at the two contacts. By measuring Hall-bar device at various temperatures from 100K to 400K, the extracted barrier height at drain contact is about 50mV larger than the one at source contact, consistent with the photocurrent and DC current observations. Photocurrent was measured at various powers and a photoresponsivity of 3.07 mA/W was extracted at low powers. When the power increases above 20uW, the photocurrent starts to saturate. Temporal response of the photocurrent is also dependent on the laser power. These studies of photocurrents and electronic transport in CVD MoS$_{\mathrm{2}}$ highlight the importance of the contacts in the electronic/optoelectronic devices and reveal the physical mechanism of the photocurrent/electronic transport in these devices. [Preview Abstract] |
|
G1.00347: Modelling large-particle diffusion in porous media as anisotropic continuous-time random walk Shahar Amitai, Raphael Blumenfeld We test the fidelity of modelling diffusion of finite-size particles in porous media by continuous-time random walk (CTRW), where the step-size and waiting-time distributions of the former, $P_l$ and $P_t$, are used as input to the latter. As the particle size is increased, the diffusion undergoes a transition from normal to anomalous. We find that, based only on $P_l$ and $P_t$, CTRW does not predict correctly this transition. We show that the discrepancy is due to the change in effective connectivity (topology) of the porous media with increasing particle size. We propose a method to capture this within the CTRW model by adding anisotropy. This adjustment yields good agreement with the simulated diffusion process, making it possible to use CTRW, with all its advantages, to model diffusion of any finite size particle in confined geometries. [Preview Abstract] |
|
G1.00348: Deformation in Thin Glassy Polymer Films from Surface towards Interior Mithun Chowdhury, Johann P. de Silva, Graham L.W. Cross Polymer thin glassy films occupy an important place in last two decades of condensed matter research, concerning its surprising surface mobility and spatially dependent structural relaxation. However, ranges of cleverly designed indirect measurements on confined polymer glassy films already probed its mechanical properties; it is still a challenging task to directly probe such small confined volume through conventional mechanical testing. We have designed confined layer compression testing with a precisely designed and aligned flat probe during nanoindentation, which was further accompanied with atomic force microscopy. Due to natural confinement from the surrounding material, we show that a state of `uniaxial strain' is created beneath the probe under small axial strains. By this methodology we are able to directly probe uniaxial flows under both anelastic and plastic conditions while doing controlled creep studies at different positions in the film starting from surface towards interior. Depending on the extent of deformation, we found ranges of effects, such as densification, anelastic yield, and plastic yield. Enhanced creep rate upon deformation supports the idea of `deformation induced mobility'. [Preview Abstract] |
|
G1.00349: Many-Body Localization in Simulation of Fermionic Systems Adrian Chapman, Akimasa Miyake In the widely-known setting of Anderson localization, noninteracting particles in a disordered potential remain confined to their initial positions, even in the infinite-time limit. Many-body localization (MBL) is the extension of this phenomenon to the regime in which the particles are weakly interacting. Recent results have demonstrated examples of many-body localized systems whose evolution may be approximately simulated classically as a result of this confinement to within a “logarithmic light cone.” Here we attempt to turn the question on its head and ask whether MBL could be used as a means of simulating quantum computations that na?vely appear difficult. We focus on one-dimensional fermionic systems, which admit techniques for classical simulation in the noninteracting case but are universal for quantum computation upon the introduction of interactions. I will describe some recent progress in this direction as well as discuss possible future endeavours. [Preview Abstract] |
|
G1.00350: Graphene-hBN-Graphene Photodetector with Low Dark Current Ruyue Zhang, Zhibo Liu Graphene is a highly promising material for high speed, broadband, and high responsivity photo detection. However, the only 2.3{\%} absorption of incident infrared-to-visible lights in graphene significantly limits their potential for applications. What is more, most of them are based on field effect transistor structures containing mechanically exfoliated graphene with high dark current, not suitable for practical large-scale device applications. We are aimed to study the photo response of pure monolayer graphene prepared by chemical vapor deposition and fabricate high efficient photodetectors by varying its structure. We performed the transfer of CVD-grown graphene by PMMA, studied the dark and photo I-V characteristics and the photosensitivity properties of pure monolayer graphene. A “graphene-hBN-graphene” structure of photodetector was designed, in which a boron nitride layer was sandwiched between two CVD graphene layers. Low dark current compared with the pure monolayer graphene photodetector was easily obtained for 532 nm incident lights due to the dielectric properties of boron nitride. And because of the low dark current, photocurrents can be easily distinguished from the background. High responsivity was obtained because incident light act on two layers of graphene simultaneously. The new structure graphene photodetector shows a great promise for a wide variety of application fields. [Preview Abstract] |
|
G1.00351: Supporting Kibble-Zurek Mechanism in Quantum Ising Model through a Trapped Ion. Changkang Hu, Jinming Cui, Yunfeng Huang, Zhao Wang, Dongyang Cao, Jian Wang, Weimin Lv, Yong Lu, Le Luo, Adolfo Campo, Yongjian Han, Chuanfeng Li, Guangcan Guo The Kibble-Zurek mechanism is the paradigm to account for the non adiabatic dynamics of a system across a phase transition. Its study in the quantum regime is hindered by the requisite of ground state cooling. We report the experimental quantum simulation of critical dynamics in the transverse-field Ising model by a set of Landau-Zener crossings in pseudo-momentum space, that can be probed with high accuracy using a single trapped ion. Our results support the Kibble-Zurek mechanism in the quantum regime and advance the quantum simulation of critical systems far-away from equilibrium. [Preview Abstract] |
|
G1.00352: Extremely Large Magnetoresistance in Bi$_{\mathrm{0.96}}$Sb$_{\mathrm{0.04}}$ Sudesh Sudesh, Pawan Kumar, Satyabrata Patnaik Recent experimental evidence for Weyl fermions in topological semimetals has attracted considerable attention. These materials are three-dimensional analogue of graphene. The present work is motivated by the recent prediction of Weyl semi-metallic phase in Bi$_{\mathrm{1-x}}$Sb$_{\mathrm{x}}$ alloys. In this paper we present the electronic transport properties studied under high applied magnetic fields in Bi$_{\mathrm{0.96}}$Sb$_{\mathrm{0.04}}$ alloys. The sample exhibits extremely high magneto-resistance; MR(5 K, 8 T) $=$ 9.8\texttimes 10$^{\mathrm{4}}$ {\%}. This value is comparable to the MR observed in recently discovered other members of these emergent materials. Most importantly, this composition shows large MR at room temperature, MR (300 K, 8 T) $=$ 435{\%}, which is almost twice to that observed in Dirac semimetal Cd$_{\mathrm{3}}$As$_{\mathrm{2}}$ ($=$ 200 {\%} at 14.5 T) and Weyl semimetal NbP ($=$ 250{\%} at 9 T). We also discuss single crystal growth techniques as well as Hall and Shubnikov de Haas (SdH) oscillation data. \textbf{References } [1] S. Singh et.al, \textit{arxiv:1512.00863v2} (2015). [2] C. Shekhar et.al, \textit{Nat. Phys.}\textbf{11} 645--650 (2015). [3] Z. Wang et.al, \textit{Phys. Rev. B} \textbf{88 }125427 (2013). [Preview Abstract] |
|
G1.00353: Observation of Superconductivity by Sr Intercalation in Topological Insulator Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ Shruti Shruti, vishal maurya, prakriti neha, sudesh sudesh, satyabrata patnaik Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ is a well-known 3D topological insulator. Here we show that Sr intercalation into the van der Waal gaps of Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ induces superconductivity with a maximum T$_{\mathrm{c}}$ of 2.9 K. The single crystals of Sr$_{\mathrm{x}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ for x$=$ 0 to 0.2 were prepared by self-flux method. The optimally doped sample Sr$_{\mathrm{0.1}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ shows a large superconducting shielding fraction of 93{\%} with T$_{c-onset}$ of 2.94 K. Using transport measurement, the anisotropy in Sr$_{\mathrm{0.1}}$Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ is found to be $\Gamma \quad =$ 1.5 with an upper critical field H$_{c2}$(0) equal to 2.1 T for magnetic field applied along the \textit{ab} plane of the sample. Along \textit{ab} plane of the sample, the lower critical field H$_{c1,ab}$(0) is estimated to be 0$.$39 \textpm 0$.$02 mT. Hall and Seebeck measurements shows electroninc carrier concentration of $n =$ 1$.$85 \texttimes 10$^{\mathrm{19}}$ cm$^{\mathrm{-3}}$ at 10 K. Such low carrier concentration indicates the possibility of unconventional pairing state. [Preview Abstract] |
|
G1.00354: Effect of a vibrating side wall on convective heat transfer in an enclosure with varying bottom wall temperature distribution Saeid Raheimpour Angeneh, Murat K. Aktas This study mainly focuses on the thermal convection in a rectangular enclosure in the presence of streaming motion while temperature profile of bottom wall is sinusoidal. The effect of wall displacement amplitude and the bottom wall temperature profile on convective heat transfer in the enclosure are determined with the help of a parametric study. By vibrating side wall of the enclosure, oscillating flow is actuated. The top wall of the enclosure is kept at initial temperature and isothermal while the side walls are adiabatic. In order to predict the oscillatory and time averaged mean flow fields, fully compressible form of the Navier -- Stokes equations are considered. Simulation of the convective transport in the enclosure is obtained by a control-volume method based, explicit computational scheme is used. The aim of this study is to provide interpretation of the flow and thermal transport physics. The influence of nonzero mean vibrational flow on the thermal convection from a surface with sinusoidal temperature distribution has never been investigated before. Conclusions may lead up to design of new heat removal applications. [Preview Abstract] |
|
G1.00355: Maximum hydrogen production from genetically modified microalgae biomass Jose Vargas, Vanessa Kava, Juan Ordonez A transient mathematical model for managing microalgae derived H$_{\mathrm{2}}$ production as a source of renewable energy is developed for a well stirred photobioreactor, PBR. The model allows for the determination of microalgae and H$_{\mathrm{2}}$ mass fractions produced by the PBR in time. A Michaelis-Menten expression is proposed for modeling the rate of H$_{\mathrm{2}}$ production, which introduces an expression to calculate the resulting effect on H$_{\mathrm{2}}$ production rate after genetically modifying the microalgae. The indirect biophotolysis process was used. Therefore, an opportunity was found to optimize the aerobic to anaerobic stages time ratio of the cycle for maximum H$_{\mathrm{2}}$ production rate, i.e., the process rhythm. A system thermodynamic optimization is conducted with the model equations to find accurately the optimal system operating rhythm for maximum H$_{\mathrm{2}}$ production rate, and how wild and genetically modified species compare to each other. The maxima found are sharp, showing up to a \textasciitilde 60{\%} variation in hydrogen production rate within 2 days around the optimal rhythm, which highlights the importance of system operation in such condition. Therefore, the model is expected to be useful for design, control and optimization of H$_{\mathrm{2}}$ production. [Preview Abstract] |
|
G1.00356: Upper and Lower Concurrence Bounds of Entanglement Swapping of Two Bell-Diagonal States Brian Kirby, Siddhartha Santra, Vladimir Malinovsky, Michael Brodsky Entanglement swapping is one of the basic operations of a quantum network. While the swapping is easily understood for fully entangled states, it is less well understood for partially mixed states. A particularly important class of mixed states which we will consider are the Bell-diagonal states, comprising a mixture of the pure Bell states. Bell-diagonal states are versatile as they can range from completely mixed to completely pure and from zero to perfect entanglement. Also Bell-diagonal states have well defined entanglement measures, such as concurrence. Therefore, an understanding of entanglement swapping with Bell-diagonal states is essential to quantum information processing and the realization of quantum networks. Here we rigorously treat the result of swapping of two, generally different, partially mixed, Bell-diagonal states and present numerical bounds on the its concurrence. In addition, we give an analytical solution for the concurrence of the state resulting from the swapping of two identical rank-two Bell-diagonal states in terms of the concurrence of the input states. Our results provide a simple method for analyzing the performance of quantum networks which utilize entanglement swapping of Bell-diagonal states. [Preview Abstract] |
|
G1.00357: Degradation mechanism of a low band gap polymer PTB7 by oxidation Soohyung Park, Junkyeong Jeong, Hyunbok Lee, Yeonjin Yi Recently, the PCE of OPVs is at the 10{\%} mark by using donor materials having a low band gap, such as poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl) (PTB7) and its analogues. In spite of the significant PCE improvement, the lifetime issue still remains open problem. To solve these technical limitations fundamentally, the degradation mechanism should be understood. It can be revealed by investigating the electronic structures of polymers with controlled exposure of oxygen, moisture and light. In this study, ultraviolet, X-ray and inverse photoelectron spectroscopy measurements were performed with step-by-step exposure of controlled oxygen, moisture and light to investigate the degradation mechanism of each polymer film. Theoretical calculations using density functional theory (DFT) were also performed to understand detailed degradation process. From the experimental results, we demonstrate that push-pull polymers are more sensitive to environmental conditions, compared with non-push-pull (conventional) polymers such as poly (3-hexylthiophene-2,5-diyl) (P3HT). In addition, we show high photo-oxidation of PTB7 is originated from the structural reason. [Preview Abstract] |
|
G1.00358: Large and high-quality single-crystal growth of cuprate superconductor Bi-2223 using the traveling-solvent floating-zone (TSFZ) method Shintaro Adachi, Tomohiro Usui, Kenta Kosugi, Nae Sasaki, Kentaro Sato, Masaki Fujita, Kazuyoshi Yamada, Takenori Fujii, Takao Watanabe In high superconducting transition temperature (high-$T_{\mathrm{c}})$ cuprates, it is empirically known that $T_{\mathrm{c}}$ increases on increasing the number of CuO$_{\mathrm{2}}$ planes in a unit cell n from 1 to 3. Bi-family cuprates are ideal for investigating the microscopic mechanism involved. However, it is difficult to grow tri-layered Bi-2223, probably owing to its narrow crystallization field. Here, we report improved crystal growth of this compound using the TSFZ method under conditions slightly different from those in an earlier report [J. Cryst. Growth 223, 175 (2001)]. A Bi-rich feed-rod composition of Bi$_{\mathrm{2.2}}$Sr$_{\mathrm{1.9}}$Ca$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{y}}$ and a slightly oxygen-reduced atmosphere (mixed gas flow of O$_{\mathrm{2}}$ (10{\%}) and Ar (90{\%})) were adopted for the crystal growth. In addition, to increase the supersaturation of the melts, we applied a large temperature gradient along the solid-liquid interface by shielding a high-angle light beam using Al foil around the quartz tube. In this way, we succeeded in preparing large ($2\times 2\times 0.05$mm$^{\mathrm{3}})$ and high-quality (almost 100{\%} pure) Bi-2223 single crystals. [Preview Abstract] |
|
G1.00359: Excitonic Lasing in Solution-Processed Subwavelength Nanosphere Assemblies. Kannatassen Appavoo, Xiaoze Liu, Vinod Menon, Matthew Sfeir Lasing in solution-processed nanomaterials has gained significant interest because of the potential for low-cost integrated photonic devices. Still, a key challenge is designing low-threshold lasing devices based on a comprehensive understanding of the system's spectral and temporal dynamics. Here we show low-threshold random lasing in sub-wavelength thin films of coupled, highly crystalline zinc oxide nanospheres, with an overall thickness on the order of $\lambda $/4. The cavity-free geometry consists of 35nm zinc oxide nanospheres that collectively localize the in-plane emissive light fields while minimizing scattering losses, resulting in excitonic lasing with fluence thresholds at least an order of magnitude lower than previous UV-blue random and quantum-dot lasers. Fluence-dependent effects, as quantified by sub-picosecond transient spectroscopy, highlight the role of phonon-mediated processes in excitonic lasing. Sub-picosecond evolution of distinct lasing modes, together with 3D electromagnetic simulations, indicate a random lasing process - in violation of the commonly cited criteria of strong scattering from individual nanostructures. These results show that coupled nanostructures with high crystallinity can function as building blocks for high-performance optoelectronics. [Preview Abstract] |
|
G1.00360: Non-saturating magnetoresistance of La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ thin films in pulsed magnetic fields up to 60T. Wei Niu, Ming Gao, Xuefeng Wang The mixed-valence manganite La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ (LSMO) is an interesting material for spintronics due to its intrinsic magnetoresistance properties. In this work, high quality LSMO films with atomic terraces are epitaxially grown on SrTiO3 (100) substrates by laser molecular beam epitaxy. The magnetoresistance of LSMO thin films has been measured in pulsed magnetic fields up to 60T over a wide temperature range. Unsaturated magnetoresistances and resistance relaxation of LSMO thin films have been found at different temperatures. Unlike polycrystalline manganites, a linear increase with fields of the magnetoconductance at low temperature which is attributed to the spin-dependent tunneling via grain boundaries. However, the unsaturation magnetoresistances of our LSMO thin films at different temperature show two kinds of trends: quadratic at low temperature; qusi-linear at high temperature. We attribute the unsaturation behavior to the scattering of domain walls. [Preview Abstract] |
|
G1.00361: Superconductive density-of-states (DOS) depletion effect manifested in interlayer magnetotransport of overdoped Bi-2212 Tomohiro Usui, Shintaro Adachi, Yuki Teramoto, Itsuhiro Kakeya, Akihiro Kondo, Koichi Kindo, Shojiro Kimura, Takao Watanabe To determine the mechanism of high superconducting transition temperature (high-$T_{c})$ superconductivity, we must understand the relationship between the pseudogap (PG) and superconductivity. For this purpose, we measure the out-of-plane resistivity $\rho_{c}$ ($T$, $H)$ of an overdoped Bi$_{\mathrm{1.6}}$Pb$_{\mathrm{0.4}}$Sr$_{\mathrm{2}}$CaCu$_{\mathrm{1.96}}$Fe$_{\mathrm{0.04}}$O$_{\mathrm{8+\delta }}$ (Bi-2212) single crystal under pulsed magnetic fields up to 60 T. Above $T_{c}$, magnetoconductivity (MC) is due to two positive components: one component rapidly increases with increasing fields but saturates at higher fields, and the other component gradually increases as $H^{\mathrm{2}}$. The former decreases with increasing temperature and vanishes around the onset temperature of superconductive fluctuation $T_{scf}$. Thus, it is attributed to the superconductive DOS depletion effect. The latter is present both below and above $T_{scf}$. Thus, it is attributed to the PG effect. Subsequent analysis below $T_{c}$ shows that the peak structure for $\rho _{c} (T$, $H)$ is primarily due to the superconductive DOS depletion effect. This result supports the scenario that the PG results in high-$T_{c}$ superconductivity. [Preview Abstract] |
|
G1.00362: First-principles path-integral molecular dynamics study of diffusion process of hydrogen in face-centered cubic metals Hajime Kimizuka, Shigenobu Ogata We investigated the H diffusivity in face-centered cubic Pd and Al by performing path-integral molecular dynamics (PIMD) modeling in the framework of density functional theory (DFT); in our calculations, we took nuclear quantum effects into consideration. The DFT results showed that the H-migration barriers ($E_{\rm m}$) in Pd and Al exhibited similar values (approximately 0.16 eV), while the H atoms were stable at octahedral (O) sites for Pd and at tetrahedral (T) sites for Al. The PIMD-based free-energy profiles for H migration between the O-site and T-site were evaluated using the thermodynamic integration of the centroid forces at 150-600 K. We confirmed that the quantum effects significantly affected the $E_{\rm m}$ and the difference between the energies of the H atom at the O-site and the T-site ($E_{\rm O-T}$); The $E_{\rm m}$ and $E_{\rm O-T}$ values in Pd at 300 K {\em increased} by 32\% and 98\%, respectively, relative to the classical limit. On the other hand, the $E_{\rm m}$ and $E_{\rm T-O}$ (i.e., $-E_{\rm O-T}$) values in Al at 300 K {\em decreased} by 3\% and 41\%, respectively. This suggested that the quantum nature of H nuclei was essential for understanding the H-diffusion kinetics in these metals even above ambient temperature. [Preview Abstract] |
|
G1.00363: Nanoscale Properties and Stability Simulations of Alkali Activated Cement Phases from First Principle Calculations Ongun Ozcelik, Claire White Using first principle density functional calculations, we present the nanoscale properties of interactions, local bonds, charge distributions, mechanical properties and strength of alkali activated cement phases which are the most promising alternative to the ordinary Portland cement with a much lower cost to the environment. We present results on the stability and long term durability of various alkali activated cement structures, effects of external alkali agents on their properties and ways of utilizing them for further applications. We compare the calculated properties of alkali activated cement with those of ordinary Portland cement and contribute to the formation of long term durability data of these phases. Comparison with X-ray and neutron scattering experiment results are also provided via pair distribution functions extracted from simulation results. [Preview Abstract] |
|
G1.00364: ABSTRACT WITHDRAWN |
|
G1.00365: Entanglement fidelity for elastic electron-electron scattering in a strongly coupled semiclassical plasmas under the influence of electric field Babatunde Falaye This study presents the effects of electric field, AB-flux field and uniform magnetic field directed along $z$-axis on electron-electron scattering encircled by a strongly coupled semiclassical plasmas. The all-inclusive effects result into a strongly repulsive system while the localizations of quantum levels change and the eigenvalues increase. We have employ perturbation formalism in our calculations. The condition $|E_{nm}^{(0)}|>>|E_{nm}^{(1)}|>|E_{nm}^{(2)}|>|E_{nm}^{(3)}|>....>|E_{nm}^{(n)}|$ holds. We find that, the combined effect of the fields is stronger than solitary effect and consequently, there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy elastic electron-electron scattering in a strongly semiclassical plasmas, a strong electric field and a weak magnetic field are required where AB-flux field can be used as a regulator. The entanglement fidelity in the scattering process is also examined. We have used partial wave analysis to derive the entanglement fidelity. We find that for a low electric field intensity, the entanglement fidelity varies with projectile energy. [Preview Abstract] |
|
G1.00366: ``Multifractals in Transmission of Off-line {\&} On-line E-Voting Systems'' WH- Maksoed An e-voting systems is a voting system in which the election data is recorded, stored {\&} processed primarily as digital information. Those are 2 type of e-voting systems: off-line {\&} on-line systems[Alaguvel {\&} Gnanavel, 2013]. ``Using transfer matrix method {\&} multifractal theory, we studied the transmission properties of 1D generalized Fibonacci structures GF(m.n) in which m {\&} n different intervals are integer according to a substitution rule[Yuannong Zhang, \textit{et.}al,:\textbf{Multifractal properties of 1D quasi-period Photonic Crystal''.} ``Transmission spectra of 1D fractal multilayer structures are found to exhibit self-similar properties'' says Zhukovsky {\&} Lavrinenko in \textbf{``Spectral self-similarity in fractal 1D photonic structures'', }\underline {Photonics {\&} Nanostructures, }2005 whereas Jacob Trevino, \textit{et.al } studies `structural properties, photonic density of state {\&} bandedge modes of Vogel spiral arrays of dielectric cylinders in air'.\underline { } [Preview Abstract] |
|
G1.00367: Comparation of clinical and paraclinical findings among patient with Kawasaki disease in Bandar abbas Koodakan Hospital in 2011-14 davood borjali Title: Comparation of clinical and paraclinical findings among patient with Kawasaki disease in Bandar abbas Koodakan Hospital in 2011-14 Kawasaki disease(KD) is a kind of vasculitis diagnosed by clinical manifestation and it caused acquired heart disease in children because of coronary arteries involvement. Method: patient divided to three group of American Japanese and incomplete and also study in two group according to fever days and then clinical features and laboratory data were checked. Result: A total of 150 patients were enrolled during the study period. number of patients with incomplete Kawasaki disease was 128 american group was 28 and Japanese was 4 patients, the most prevalent symptom was scaling of extremities(61%) and then strawberry taunge(47/9%). 100% patients in Japanese group had anemia and extremities scaling. there were significant differences between three group of criteria in Season age rash and conjectivitis.in groups with fever days rash lymphadenopathy conjectivitis and extremity involvement were most seen in group with fever less than five days. But thrombocytosis ,increased ESR and CRP, cardiac and gall bladder most seen in group with fever more than five days. Keyword: Kawasaki , epidemiology , criteria [Preview Abstract] |
|
G1.00368: ``OPTICAL CATALYTIC NANOMOTORS'' Glory Rosary-OYONG,SE D. Kagan, \textit{et.al, } 2009:'' a motion-based chemical sensing involving fuel-driven nanomotors is demonstrated. The new protocol relies on the use of an optical microscope for tracking charge in the speed of nanowire motors in the presence of target analyte''. Synthetic nanomotors are propelled by catalytic decomposition of .. they do not require external electric, magnetic or optical fields as energy..\textless pubs.acs.org/cen/science/83/i08/8308sci1.html\textgreater . Accompanying Fig 2.6( a ) of optical micrograph of a partial monolayer of silica microbeads [J.Gibbs, 2011 ] retrieves WF Paxton:''rods were characterized by transmission electron {\&} dark-field optical microscopy..'' {\&} LF Valadares:''dimer due to the limited resolution of optical microscopy, however the result..'. [Preview Abstract] |
|
G1.00369: Probing voltage induced bond rupture in a molecular junction Haixing Li, Timothy Su, Nathaniel Kim, Pierre Darancet, James Leighton, Michael Steigerwald, Colin Nuckolls, Latha Venkataraman We use scanning tunneling microscope break junction to study electric field breakdown at the single molecule level. We investigate breakdown phenomena in atomic chains composed of Si---Si, Si---O, Si---C, Ge---Ge and C---C bonds that are commonly found in the low-$\kappa$ dielectric material. We see different bond rupture behaviors in a range of molecular backbones, and use the results from a statistically large number of measurements to determine which bond breaks. We find that Si---Si and Ge---Ge bonds rupture above a 1V bias. We also find that the Si---C bond is more robust than Si---O or Si---Si bond at above 1V. Finally, we illustrate how an additional conductance pathway in parallel to the Si---Si bond changes bond rupture behavior under an electric field. We carry out ab initio calculations on these systems and demonstrate that the mechanism for bond rupture under electric field involves {\lq\lq}heating{\rq\rq} of the molecule through electron-vibrational mode coupling. [Preview Abstract] |
|
G1.00370: On the magnetic structure and band gap of the double perovskite Ba2CuOsO6: Density functional analysis Changhoon Lee, Jisook Hong, Ji Hoon Shim, Myung-Hwan Whangbo The ordered double-perovskite Ba$_{\mathrm{2}}$CuOsO$_{\mathrm{6}}$, consisting of 3d and 5d transition-metal magnetic ions (Cu$^{\mathrm{2+}}$ and Os$^{\mathrm{6+}}$, respectively), is a magnetic insulator. It obeys the Curie-Weiss law with $\theta \quad =$ -13.3 K. We evaluated the spin exchange interactions of Ba$_{\mathrm{2}}$CuOsO$_{\mathrm{6}}$ by performing energy-mapping analysis based on DFT$+$U calculations and determined the band gap of Ba$_{\mathrm{2}}$CuOsO$_{\mathrm{6}}$ by DFT$+$U and DFT$+$U$+$SOC calculations. The antiferromagnetic ordering of Ba$_{\mathrm{2}}$CuOsO$_{\mathrm{6}}$ is due largely to the spin exchange interactions between Cu2$+$ ions, which are enhanced by the empty eg orbitals of the intervening Os$^{\mathrm{6+}}$ ions. Both electron correlation and spin-orbit coupling are necessary to open a band gap for Ba$_{\mathrm{2}}$CuOsO$_{\mathrm{6}}$. [Preview Abstract] |
|
G1.00371: Local nature of impurity induced spin-orbit torques Sergey Nikolaev, Alan Kalitsov, Mairbec Chshiev, Oleg Mryasov Spin-orbit torques are of a great interest due to their potential applications for spin electronics. Generally, it originates from strong spin orbit coupling of heavy 4d/5d elements and its mechanism is usually attributed either to the Spin Hall effect or Rashba spin-orbit coupling. We have developed a quantum-mechanical approach based on the non-equilibrium Green's function formalism and tight binding Hamiltonian model to study spin-orbit torques and extended our theory for the case of extrinsic spin-orbit coupling induced by impurities. For the sake of simplicity, we consider a magnetic material on a two dimensional lattice with a single non-magnetic impurity. However, our model can be easily extended for three dimensional layered heterostructures. Based on our calculations, we present the detailed analysis of the origin of local spin-orbit torques and persistent charge currents around the impurity, that give rise to spin-orbit torques even in equilibrium and explain the existence of anisotropy. [Preview Abstract] |
|
G1.00372: An Experimental and Modeled Comparison of Diffraction in Imaging Systems Spencer Ketchum, Wilbert Slowman, Megan Paciaroni The resolution limit of imaging systems is always ultimately limited by diffraction. However, diffraction is often neglected in the analysis and design of both front and back illumination imaging systems in favor of the simpler ray tracing model. In many systems, paraxial optics provides a reasonable model for the design of systems with high resolution. This is certainly true for the majority of front-illuminated imaging systems; however, in back illuminated (shadowgraphic) imaging systems resolution is very strongly affected by diffraction. In this paper, we present a detailed experimental comparison of imaging resolution differences between front and back illuminated imaging systems for non-scattering and scattering environments. Additionally, modeling results of both systems are compared with the experimental results and classical optical theory. Preliminary results and calculations show that physical optics creates a stronger effect on resolution in back illuminated systems in either scattering or non-scattering environments. [Preview Abstract] |
|
G1.00373: \textbf{Emergent Magnetism in Mesoporous Materials} Sher Alam, Ajayan Vinu We discuss the emergence of magnetism in Mesoporous Materials. We have obtained experimental results showing a variety of magnetic behaviors arising, by using different types of mesoporous or nanoporous templates. Since the templates allow different magnetic properties to arise naturally we have dubbed this as dynamic templating method. Our procedure and realization incidentally demonstrates the idea of Nanoarchitectonics proposed by Aono, as a MANA concept. Which, simply means to allow different nano-blocks to interact to obtain a certain desired structure and properties. [Preview Abstract] |
|
G1.00374: ``Heavy-water Lattice and Heavy-Quark'' WH- Maksoed,SSi Refer to Birgitt Roettger-Roessler: \textbf{``Feelings at the Margins''}, 2014 retrieved the Vienna, 2006 UNIDO Research Programme: Combating Marginalization and Poverty through Industrial Development/COMPID. Also from Vienna, on Feb 18-22, 1963 reported Technical Report Series 20 about \textbf{``Heavy Water Lattice'' }. Failed to relates scale-invariant properties of public-Debt growth to convergence in perturbation theory, sought JH Field: \textbf{``Convergence {\&} Gauge Dependence Properties:..''.} Furthers, in GP Lepage: \textbf{``On the Viabilities of Lattice Perturbation Theory'', } 1992 stated: ``in terms of physical quantities, like the heavy-quark potential, greatly enhanced the predictive power of lattice perturbation theory''. [Preview Abstract] |
(Author Not Attending)
|
G1.00375: Enhanced charge transport in highly conducting PEDOT-PSS films after acid treatment V. Akshaya Shiva, Ravi Bhatia, Reghu Menon The high electrical conductivity, good stability, high strength, flexibility and good transparency of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS), make it useful for many applications including polymeric anodes for organic photovoltaics, light-emitting diodes, flexible electrodes, supercapacitors, electrochromic devices, field-effect transistors and antistatic-coatings. However, the electrical conductivity of PEDOT-PSS has to be increased significantly for replacement of indium tin oxide (ITO) as the transparent electrode in optoelectronic devices. The as prepared (pristine) PEDOT-PSS film prepared from the PEDOT-PSS aqueous solution usually has conductivity below 1Scm$^{\mathrm{-1}}$, remarkably lower than ITO. Significant conductivity enhancement has been observed on transparent and conductive PEDOT-PSS films after a treatment with inorganic acids. Our study investigates the charge transport in pristine and H$_{\mathrm{2}}$SO$_{\mathrm{4}}$, HNO$_{\mathrm{3}}$, HCl treated PEDOT-PSS films. We have treated the films with various concentrations of acids to probe the effect of the acid treatment on the conduction mechanism. The study includes the measurement of dc and electric field dependent conductivity of films in the temperature range of 4.2K-300K. We have also performed magneto-resistance measurements in the range of 0-5T. An enhancement by a factor of\textasciitilde 10$^{\mathrm{3}}$ has been observed in the room temperature conductivity. The detailed magneto-transport studies explain the various mechanisms for the conductivity enhancement observed. [Preview Abstract] |
|
G1.00376: ABSTRACT WITHDRAWN |
(Author Not Attending)
|
G1.00377: Collective organization in aerotactic motion Marco G. Mazza Some bacteria exhibit interesting behavior in the presence of an oxygen concentration. They perform an aerotactic motion along the gradient until they reach their optimal oxygen concentration. But they often organize collectively by forming dense regions, called ’bands’, that travel towards the oxygen source. We have developed a model of swimmers with stochastic interaction rules moving in proximity of an air bubble. We perform molecular dynamics simulations and also solve advection-diffusion equations that reproduce the aerotactic behavior of mono-flagellated, facultative anaerobic bacteria. If the oxygen concentration in the system sinks locally below a threshold value, the formation of a migrating aerotactic band toward the bubble can be observed. [Preview Abstract] |
|
G1.00378: Estimating topological properties of weighted networks from limited information Andrea Gabrielli, Giulio Cimini, Diego Garlaschelli, Angelo Squartini A typical problem met when studying complex systems is the limited information available on their topology, which hinders our understanding of their structural and dynamical properties. A paramount example is provided by financial networks, whose data are privacy protected. Yet, the estimation of systemic risk strongly depends on the detailed structure of the interbank network. The resulting challenge is that of using aggregate information to statistically reconstruct a network and correctly predict its higher-order properties. Standard approaches either generate unrealistically dense networks, or fail to reproduce the observed topology by assigning homogeneous link weights. Here we develop a reconstruction method, based on statistical mechanics concepts, that exploits the empirical link density in a highly non-trivial way. Technically, our approach consists in the preliminary estimation of node degrees from empirical node strengths and link density, followed by a maximum-entropy inference based on a combination of empirical strengths and estimated degrees. Our method is successfully tested on the international trade network and the interbank money market, and represents a valuable tool for gaining insights on privacy-protected or partially accessible systems. [Preview Abstract] |
|
G1.00379: ABSTRACT MOVED TO F43.013 |
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