Bulletin of the American Physical Society
Joint Spring 2012 Meeting of the Texas Sections of the APS and AAPT and Zone 13 of the SPS
Volume 57, Number 2
Thursday–Saturday, March 22–24, 2012; San Angelo, Texas
Session E2: Contributed Oral Presentations: APS 4 |
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Chair: Timothy Renfro, McMurry University Room: Houston Harte University Center UC 201 |
Friday, March 23, 2012 3:30PM - 3:42PM |
E2.00001: First-principles study of the electronic structure of NiS, NiS$_{2}$, and Ni$_{3}$S$_{2}$ Joaquin Noyola, Qiming Zhang First-principles study of the electronic structure of NiS, NiS$_{2}$, and Ni$_{3}$S$_{2}$ are performed. DFT+U and HSE hybrid functional are used as the primary exchange-correlation schemes. The resulting electronic structures at various phases are analyzed, and the results compared with previous experimental and theoretical work. [Preview Abstract] |
Friday, March 23, 2012 3:42PM - 3:54PM |
E2.00002: GaN HEMTs Jonathan W. Anderson, Kyoung-Keun Lee, Edwin L. Piner Gallium nitride (GaN) has enormous potential for applications in high electron mobility transistors (HEMTs) used in RF and power devices. Intrinsic device properties such as high electron mobility, high breakdown voltage, very high current density, electron confinement in a narrow channel, and high electron velocity in the 2-dimensional electron gas of the HEMT structure are due in large part to the wide band gap of this novel semiconductor material system. This presentation discusses the properties of GaN that make it superior to other semiconductor materials, and outlines the research that will be undertaken in a new program at Texas State University to advance GaN HEMT technology. This program's aim is to further innovate the exceptional performance of GaN through improved material growth processes and epitaxial structure design. [Preview Abstract] |
Friday, March 23, 2012 3:54PM - 4:06PM |
E2.00003: Optical Properties of dual ion beam sputtered Indium Tin Oxide films on glass and Silicon Nelson Simpson, Wilhelmus Geerts, Anup Bandyopadhyay Indium Tin Oxide (ITO) is a transparent conducting material that finds application in flat panel displays, solar cells, and photodetectors. High quality ITO films, i.e. films with a large transparency and a high conductivity, are normally deposited above room temperature often at 300-400 C. This high deposition temperature eliminates most plastics as substrates. To lower the substrate deposition temperature we are applying atomic instead of molecular oxygen during the sputtering process. A dual ion beam sputtering system (DIBS) has been modified to allow the substrate to be exposed to an atomic oxygen beam at 45 degrees angle of incidence. Thin films were sputtered as a function of atomic oxygen flux and substrate temperature on glass, silicon, and sapphire substrates. The optical properties were measured by spectroscopic ellipsometry, reflectometry, and FTIR. Film thickness and bandgap were determined from the optical properties in the visible part of the spectrum. Mobility was determined from the infrared part of the spectruam. Optical properties appear to vary with the film thickness, the oxygen flux, and the substrate temperature. Roughness of the samples was independently measured by AFM. This work is supported by a grant from research corporation (10775). [Preview Abstract] |
Friday, March 23, 2012 4:06PM - 4:18PM |
E2.00004: Using MuSR to probe internal magnetic field features in the II-IV-V2:Mn DMS Patrick Mengyan, R.L. Lichti, Y.G. Celebi, B.B. Baker, L. Hudy, E. Catek, K.T. Zawilski, P.G. Schunemann Muon Spin \underline {R}esearch/\underline {R}otation/\underline {R}elaxation/\underline {R}esonance (MuS\underline {R}) is a technique that utilizes 100{\%} spin polarized muons as a very sensitive probe of a material's local magnetic and electronic environment. In this contribution, I will give a brief review of the Longitudinal Field Muon Spin Relaxation technique and present preliminary results as applied to investigating local magnetic features in weakly Mn doped ZnGeP$_{2 }$Chalcopyrite semiconductors. The discovery of room temperature ferromagnetism in some of the II-IV-V$_{2}$ dilute magnetic systems as well as their conventional semiconducting properties makes these materials prime candidates for prospective use in the field of spin-electronics. The mechanism responsible for connecting the local magnetic features to the bulk magnetic properties is not yet understood. The MuSR technique and the preliminary results presented here are promising first steps in the investigation and attempt to further the understanding of the local magnetic features in these dilute magnetic semiconducting materials. [Preview Abstract] |
Friday, March 23, 2012 4:18PM - 4:30PM |
E2.00005: Electrochemical Performance of Lithium Iron Phosphate Doped with Tungsten Hanu Arava, Lulu Zhang, Hui Fang, Gan Liang Due to its high thermal stability, low cost and high theoretical charge capacity, LiFePO4 has emerged as one of the most promising cathode materials for large-scale lithium ion batteries. In this work, we systematically investigated the effect on structure and electrochemical properties brought by W doping on Fe site of LiFePO$_{4}$. LiFe$_{1-x}$W$_{x}$PO$_{4}$ (x= 0. 0.01, 0.02, 0.03) samples with and without carbon coating were prepared by using solid-state reaction. The phase and structure of as prepared powders were characterized by X-ray diffraction and scanning electron microscope. Cycling charge and discharge measurement at various C-rates and cyclic voltammetry were employed to reveal the electrochemical properties. Results showed that carbon coating dramatically improved the capacity at fast C-rate. 2 at.{\%} W doping was observed to have the highest charge capacity with 143 mAh/g at 0.1C and a 109 mAh/g for 1C. [Preview Abstract] |
Friday, March 23, 2012 4:30PM - 4:42PM |
E2.00006: Photoluminescence Study of Nanodiamond Defects Joseph Kimball, T.W. Zerda, B. Rout, Anastasiia Nemashkalo The unique properties of photoluminescent nanodiamonds make them a preferred candidate for optical labels in biological and medical imaging. To fully implement and understand their optical and physical properties, this study used two different techniques to create in TEM confirmed nanocrystal size range of 5 to 125 nm, the nitrogen vacancy (N-V) defects responsible for the emission of a photostable spectrum from 500-800 nm. The basic theory behind the diamond crystal lattice and point defects responsible for the light emitting nitrogen vacancy (N-V) center are presented. Two different methods, irradiation and high pressure-high temperature (HPTHP), are used to create the sought after (N-V) center. Photoluminescence results correlated with FTIR spectroscopy allowed the determination of the PL intensity relation to various defects, crystal size and nitrogen concentration. [Preview Abstract] |
Friday, March 23, 2012 4:42PM - 4:54PM |
E2.00007: Spin Effects in isolated mono- and bilayer molybdenum disulfide Nanowires Lucas Fern\'andez Seivane, X\'ochitl L\'opez-Lozano Inspired by the recent synthesis of needle-like MoS$_2$ nanoparticles, we have investigated the properties of isolated quasi-one dimensional MoS$_2$ nanowires. These nanostructures deserve a special interest since they constitute one of the smallest self-supported MoS$_2$ systems with promising catalytic properties. A complete description of the edge, electronic and spin properties for different sulfur saturations is extremely important for the future developments of novel MoS$_2$-based nanocatalysts. In this work we have performed ab initio simulations within the Density Functional Theory framework with the \textsc{Siesta} code to study the structural, electronic and spin properties of quasi-one dimensional MoS$_2$ Nanostructures. We observed that a change in the number of Mo atoms on the unit cell affects greatly the electronic properties. Interestingly, metallic states are found in all the low-energy models. Also, both for mono- and bilayer the spin states are also localized at the active nanowire edges. We also noticed the presence of a variety of spin regimes suggesting the connection between magnetism and its catalytic properties. In spite of the observed pairing of S dimers at the Mo-edge in some cases, we do not observe a Peierls-like metal-insulator transition. [Preview Abstract] |
Friday, March 23, 2012 4:54PM - 5:06PM |
E2.00008: Sytematic Study of the Adsorption of Thiol Molecules on Noble-Metal Nanoparticles H. Barron, F. Hidalgo, L. Fernandez-Seivane, C. Noguez, X. Lopez-Lozano The study of the interaction between nanoparticles and different types of ligands has been intensively investigated in the last years due to the potential contribution of their properties to the nanotechnology device design. These properties have opened new research fields like plasmonics, with interesting applications in optics, electronics, biophysics, medicine, pharmacology and materials science. Self-assembly monolayers have been thoroughly studied at experimental and theoretical level on extended (111) gold and silver surfaces. However, nanoparticle and molecule properties after the adsorption are still not well understood due to the different factors involved in this process such as the adsorption sites, size and element type of the nanoparticle. In this work we have performed a systematic study of the adsorption of methyl-thiol molecules on Au$_{55}$ and Ag$_{55}$ clusters through density functional theory calculations with the SIESTA code. Different adsorption modes of the methyl-thiol molecule on Au$_{55}$ and Ag$_{55}$ were considered. In general, for both type of nanoparticles, the methyl-thiol molecule prefers to be adsorbed on the Bridge sites. These results provide valuable information of the structural and electronic properties of methyl-thiol passivated Au and Ag nanoparticles. [Preview Abstract] |
Friday, March 23, 2012 5:06PM - 5:18PM |
E2.00009: Composition Dependence of the Properties of Noble-metal Nanoalloys Lucas Fern\'andez Seivane, H\'ector Barr\'on, James Benson, Hans-Christian Weissker, Xochitl L\'opez-Lozano Bimetallic nanostructured materials are of greater interest both from the scientific and technological points of view due to their potential to improve the catalytic properties of novel materials. Their applicability as well as the performance depends critically on their size, shape and composition, either as alloy or core-shell. In this work, the structural, electronic, magnetic and optical properties of bimetallic Au-Ag nanoclusters have been investigated through density-functional-theory-based calculations with the Siesta and Octopus codes. Different symmetries -tetrahedral, bipyramidal, decahedral and icosahedral- of bimetallic nanoparticles of 4-, 5-, 7- and 13-atoms, were taken into account including all the possibly different Au:Ag ratio concentrations. In combination with a statistical analysis of the performed calculations and the concepts of the Enthalpy of Mixing and Energy Excess, we have been able to predict the most probable gap and magnetic moment for all the composition stoichiometries. This approach allows us to understand the energy differences due to cluster shape effects, the stoichiometry and segregation. In addition, we can also obtain the bulk energy and surface energy of Au-Ag nanoalloys by looking at fixed number of atoms and fixed morphologies. [Preview Abstract] |
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