Bulletin of the American Physical Society
Joint Fall 2009 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 54, Number 13
Thursday–Saturday, October 22–24, 2009; San Marcos, Texas
Session G1: Condensed Matter Physics III |
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Chair: Carl Ventrice, Texas State University - San Marcos Room: LBJ Student Center 3-9.1 |
Saturday, October 24, 2009 10:00AM - 10:12AM |
G1.00001: Friction effects on force measurements at the bottom of a granular column Sam McKenzie, Randy Back We report on systematic force measurements at the bottom of a silo for several granular materials. We look at the dependence of the force measurements on the coefficient of friction. We compare our results to theoretical predictions. [Preview Abstract] |
Saturday, October 24, 2009 10:12AM - 10:24AM |
G1.00002: Temperature dependence of the internal piezoelectric field in a single InGaAs strained quantum well Matthews James, Toni Sauncy In this work, the photoluminescence (PL) emission from a $<$111$>$-grown InGaAs/GaAs quantum wells which contains a strain-generated piezoelectric field in the quantum well active area has been investigated as a function of temperature over the range of 35K to 175K. At each temperature, changes to the PL spectrum as a function of incident excitation intensity were examined. The PL data indicated that the standard empirical models are inadequate for use in fitting the PL vs. T data and implying that the complications of strain and internal field must be included in understanding the emission temperature dependence. In order to experimentally determine the value of the internal field, the PL excitation intensity-dependence data full width at half maxima were examined. Using the relationship between potential difference, well width and the standard definition of the electric field, the internal field in this well was determined to vary from 36.7kV/cm(35K) to 11kV/cm(85K). This indicates that the electric field within the quantum well is not constant over this temperature range. [Preview Abstract] |
Saturday, October 24, 2009 10:24AM - 10:36AM |
G1.00003: Evaluation and simulation of MEMS cantilever relays Jason Williams, Casey Smith, Anup Bandyopadhyay, Gregory Spencer Electrostatically-actuated MEMS cantilevers were fabricated for testing as a potential replacement for nanoscale circuit components in low power applications like spacecraft. These cantilevers are operated in a horizontal plane by applying a voltage to side electrodes. The polysilicon cantilevers were fabricated at SEMATECH with a range of beam lengths (from 2 to 14 $\mu $m) and electrode gap spacings (from 110 nm to 140 nm). The cantilevers were tested to determine the voltage required to bring the beam into contact with the collector. This pull-in voltage was measured as a function of device dimensions. To simulate the device operation, a model was created in MEMS simulation software. Simulations of pull-in voltage and time were compared to the data to validate the model and estimate the frequency response of the devices. Variations of model device parameters such as beam thickness, height, gap size, and Young's modulus were used to define a design space based on power requirements. SEM images were obtained to study failure mechanisms of some tested devices. This work is systematically evaluating the effects of device dimensions on the operation and failure mechanisms of nanoscale cantilevers for low power applications. [Preview Abstract] |
Saturday, October 24, 2009 10:36AM - 10:48AM |
G1.00004: Development of Etch Processes for High-k Dielectric CMOS Devices with LaO$_{x}$/HfO$_{2}$ and LaO$_{x}$/HfSiO Gate Oxides Kelly Rader, Carl Ventrice, Patrick Lysaght High-k dielectric CMOS devices for low standby power applications require a low workfunction oxide on the n-MOSFET side of the CMOS device to reduce the threshold voltage and gate leakage. A promising candidate for this application is LaO$_{x}$. However, a process for etching the LaO$_{x}$ from the p-MOSFET, which leaves the n-side intact, is required. A wet etch study, which enables the creation of a simplified process flow for CMOS devices using LaO$_{x}$ on the n-side intact, is presented. The oxidation states and stoichiometry of the LaO$_{x}$ films is investigated via x-ray photoelectron spectroscopy (XPS). [Preview Abstract] |
Saturday, October 24, 2009 10:48AM - 11:00AM |
G1.00005: Hyperfine Spectroscopy and Characterization of Muonium Centers in ZnGeP$_{2}$ Patrick Mengyan, B.B. Baker, R.L. Lichti, K.H. Chow, Y.G. Celebi, K.T. Zawilski, P.G. Schunemann We have recently initiated a study of the defect states formed when positive muons are implanted into chalcopyrite structured II-IV-V$_{2}$ compounds to extend our investigation of the muonium defect centers as an experimentally accessible analog of isolated hydrogen defect states in semiconductors. In this presentation, I will discuss one of the initial observations of neutral muonium defect centers in ZnGeP$_{2}$; specifically, the hyperfine characterization of the neutral muonium centers observed in ZnGeP$_{2}$ using the Muon Spin Relaxation technique (MuSR). The spin precession frequencies in a field of 4.0 Tesla yield a zero-temperature hyperfine constant of $\sim $1962 MHz for the promptly formed Mu$^{0}$ state. Subsequently, we performed T$_{1}^{-1}$ longitudinal depolarization measurements in low magnetic fields. Decoupling curves show a different anisotropic Mu$^{0}$ with A$_{2}$=3185 MHz and D=374 MHz, where the D is the dipolar contribution. I will report on the spectroscopic hyperfine characterization of the neutral muonium centers observed in ZnGeP$_{2}$. [Preview Abstract] |
Saturday, October 24, 2009 11:00AM - 11:12AM |
G1.00006: Characterization of the Motion of Muonium centers in II-IV-V$_{2}$ Semiconductors Brittany Baker, Patrick Mengyan, Roger Lichti, Gurkan Celebi, Kim Chow, Kevin Zawilski, Peter Schunemann Recent Muon Spin Research (MuSR) has been done to investigate properties of II-IV-V$_{2}$ chalcopyrite semiconductor materials. This work has shown that some of the materials appear to have only diamagnetic muonium centers while ZnGeP$_{2}$ has multiple neutral muonium centers along with the diamagnetic muonium center. Results for ZnGeP$_{2}$ show two distinct interstitial tetrahedral sites (T-sites). At low temperatures, neutral muonium hops between sites by quantum tunneling. Thermally activated hopping takes place from about 100K to 220K and at higher temperatures ionization occurs. Hop rates have been obtained from longitudinal field MuSR depolarization measurements. Preliminary results of motion in II-IV-V$_{2}$ samples with diamagnetic muonium centers will be presented. [Preview Abstract] |
Saturday, October 24, 2009 11:12AM - 11:24AM |
G1.00007: Measuring Phonon Velocities in CaWO$_{4}$ with Phonon Imaging Timothy Head, Madeleine Msall A recent search for dark matter by the CRESST experiment seeks to observe dark matter collisions with nuclei of CaWO$_{4}$ using low temperature bolometric detectors which are sensitive to energy deposition on the order of 10 keV with a few percent accuracy. Determination of the amount of energy deposited depends upon details of the non-equilibrium heat flow in the absorber crystals. Our phonon images are sensitive to small angular variations in the phonon flux, and can provide phonon group-velocity data along symmetry and non-symmetry directions. [Preview Abstract] |
Saturday, October 24, 2009 11:24AM - 11:36AM |
G1.00008: Borozene: A Building Block of Boron Nanostructures Nevill Gonzalez Szwacki, Valery Weber, Christopher J. Tymczak Bulk boron exhibits a complex crystal structure due to its electron-deficient bonds, and in all known forms is semiconducting. However, there is little known about the properties of boron at the nanometer scale. For example, it has been experimentally reported that boron can form nanotubes that are metallic; however, the structure of these nanotubes remains still unknown [1]. Based on first principles calculations we present a theoretical investigation on the structure and electronic properties of all-boron and boron related nanostructures. Special emphasis will be placed on our recent work [2] on the theoretical identification of an unusually stable planar molecule, B12H6, which has similar structural and electronic properties to the well-known benzene. We investigate this molecule as a promising building block of boron hollow nanoclusters and nanotubes.\\[4pt] [1] D. Ciuparu, R. F. Klie, Y. Zhu, L. D. Pfefferle, Journal of Physical Chemistry B 108, 3967 (2004)\\[0pt] [2] N. Gonzalez Szwacki, V. Weber, and C. J. Tymczak, Nanoscale Res. Lett. 4, 1085 (2009). [Preview Abstract] |
Saturday, October 24, 2009 11:36AM - 11:48AM |
G1.00009: Magneto-Optical Kerr Spectra in (Ga, Mn)As Yong Hee Cho, Aleksander Wojcik, Alexey Belyanin, Chanjuan Sun, Junichiro Kono, Hiro Munekata We theoretically and experimentally investigated the magneto-optical Kerr effect (MOKE) in ferromagnetic (Ga, Mn)As over a broad spectral range with varying Mn concentration and hole density. The full band structure was obtained with a 30 band k.p method with the exchange interaction between Mn spins and itinerant holes. The dielectric tensor and Kerr spectra were calculated for the interband transitions over the first Brillouin zone. Theoretical results show excellent agreement with experimental Kerr spectra. Our studies prove antiferromagnetic character of p-d exchange interaction between holes and Mn moments. They confirm that the Fermi level in our GaMnAs samples lies in the valence band and the Kerr rotation originates from the interband transitions, and not from the impurity band-related transitions. Also, the strain and the spin-orbit band effects on MOKE are discussed. [Preview Abstract] |
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