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 B1: Condensed Matter Physics I |
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Chair: Casey Smith, Sematech Room: LBJ Student Center 3-14.1 |
Friday, October 23, 2009 10:00AM - 10:12AM |
B1.00001: Origins and Properties of Uncompensated Magnetization in FeF$_{2}$ Karie Badgley, Mikhail Zhernenkov, Michael R. Fitzsimmons, Igor V. Roshchin Recent studies\footnote{M.R. Fitzsimmons et al. Phys. Rev. B \textbf{75}, 214412 (2007).} of exchange bias demonstrated uncompensated magnetization in an antiferromagnet. To further investigate the properties and the origin of this magnetization, two types of 36nm thick samples of FeF$_{2}$ on MgF$_{2}$ were prepared: with and without a 3nm top layer of Al used to prevent possible oxidation. SQUID VSM measurements on these samples showed uncompensated magnetization. Samples coated with Al were found to have larger magnetic susceptibility. These findings are in agreement with neutron scattering measurements, which also showed the uncompensated magnetization primarily at the top surface of FeF$_{2}$ for the Al-coated sample. The temperature dependence and possible origin of the uncompensated magnetization will be discussed. Funded by Texas A{\&}M University and Texas A{\&}M University -- CONACyT Collaborative Research Grant Program. [Preview Abstract] |
Friday, October 23, 2009 10:12AM - 10:24AM |
B1.00002: High Coverage Oxidation of the Cu(001) Surface: A Density Functional Study W.B. Maddox, N.G. Fazleev The study of oxygen adsorption on transition metal surface is important for the understanding of corrosion, heterogeneous catalysis, and oxide growth. The structures formed on oxidized transition metal surfaces vary from simple adlayers of chemisorbed oxygen to more complex structures which result from the diffusion of oxygen into sub-surface regions. In this paper, an ab-initio investigation of stability and associated physical and electronic properties of different adsorption phases of oxygen on the Cu(001) missing row reconstructed surface using density functional theory in the generalized gradient approximation, is presented. Results of calculations regarding geometrical as well as electronic properties including changes in electron work function, difference electron density and density of states as a function of oxygen coverage are also discussed. Furthermore, the chemistry of metal-adsorbate bonding is studied with primary interest being paid to high coverage oxygen adsorption. [Preview Abstract] |
Friday, October 23, 2009 10:24AM - 10:36AM |
B1.00003: Electronic Properties of the Prussian Blue Analog Co$_{3}$[Os(CN$_{6}$)]$_{2}$ at Low Temperatures T. Wellington, A. Ford, W. Teizer, M. Hilfiger, C. Avendano, K. Dunbar The Prussian blue analog Co$_{3}$[Os(CN$_{6})$]$_{2}$ exhibits photoinduced changes of magnetic behavior as well as charge transfer induced spin transitions at low temperatures (5-10K). Magnetic measurements on the bulk material show an increased magnetic susceptibility after illumination with red light, as the analog exhibits an abrupt spin transition due to enhanced cooperativity. We are studying the electronic interactions between this Prussian blue analog and gold films of varying thickness at temperature 2K$<$T$<$300K, in order to analyze the effect of the introduction of new materials into the Prussian Blue vacancies. We show that the bilayer of the Prussian Blue analog Co$_{3}$[Os(CN$_{6})$]$_{2}$ and gold exhibits a decrease by an approximate factor of three in the resistance when compared to a thin film gold sample. The exact decrease varies from sample to sample, due to the disordered nature of Prussian blue analogs and the existence of water in the interstices of the lattice. However, for each sample the observed decrease is reproducible for up to two weeks. [Preview Abstract] |
Friday, October 23, 2009 10:36AM - 10:48AM |
B1.00004: Introduction to Time of Flight Positron Annihilation Induced Auger Spectroscopy (TOF-PAES) Prasad Joglekar, Sushant Kalaskar, Karthik Shastry, Suman Satyal, Alex Weiss Time of flight- positron annihilation induced auger electron spectroscopy (TOF-PAES) is extremely surface selective with close to 95{\%} of the PAES signal stemming from the top-most atomic layer. In PAES, a beam of low energy (1eV -- 25eV) positrons is made incident on a surface where they become trapped in an image potential well. A fraction (up to several percent) of the positrons in the surface state annihilate with the core electrons of atoms at the surface resulting in core-holes. Electrons in higher levels can fill these core-hole via an Auger transition in which the energy associated with this filling the core hole is transferred to another electron which can leave the atom and the surface. The energy of the outgoing (Auger) electrons is characteristic of the energy levels of the atom and can be used to identify the specific element taking part in the transition. In this talk I will present a brief review of how the TOF PAES technique can be used to obtain Auger spectra that is completely free of secondary electron background. [Preview Abstract] |
Friday, October 23, 2009 10:48AM - 11:00AM |
B1.00005: Design of an Operando Positron Annihilation Gamma Spectrometer (OPAGS) Suman Satyal, Kartik Shastry, Sushant Kalaskar, Larry Lim, Vibek Joglekar, Alexander Weiss Surface properties measured under UHV conditions cannot be extended to surfaces interacting with gases under realistic pressures due to surface reconstruction and other strong perturbations of the surface. Many surface probing techniques used till now have required UHV conditions to avoid data loss due to scattering of outgoing particles. Here we describe the design of an Operando Positron Annihilation Gamma Spectrometer (OPAGS) currently under construction at the University of Texas at Arlington. The new system will be capable of obtaining surface and defect specific chemical and charge state information from surfaces under realistic pressures. Differential pumping will be used to maintain the sample in a gas environment while the rest of the beam is under UHV. The Elemental content of the surface interacting with the gas environment will be determined from the Doppler broadened gamma spectra. This system will also include a time of flight (TOF) positron annihilation induced Auger spectrometer (TOF-PAES) for use in combined annihilation induced Auger and annihilation gamma measurements made under low pressure conditions. [Preview Abstract] |
Friday, October 23, 2009 11:00AM - 11:12AM |
B1.00006: Auger Photo Electron Spectroscopy (APECS) measurement of the low energy tail (LET) of Cu MVV and Ag NVV Auger peak down to 0 eV K. Shastry, A.H. Weiss, R.A. Bartynski, S.L. Hulbert The low energy Auger peak sit on large background due to secondary electrons that arise from loss processes unrelated to the Auger process. Auger photoelectron coincidence spectroscopy (APECS) technique was used to probe the surfaces of Cu (100) and Ag (100) to suppress background unrelated to the auger process and obtain the energy distribution of the electrons emitted as a result of the MVV transition in Cu and NVV transition in Ag over the full range of emitted energies (0eV-81eV). The measurements reveal a well formed auger peak at 40 eV and 60 eV for Cu and Ag respectively accompanied by a significant back ground in the low energy region of the spectrum. The origins of the low energy tail (LET) are discussed in terms of extrinsic mechanisms in which the electrons from the peak lose energy as they propagate to the sample surface, as well as intrinsic mechanisms in which multi- electron auger processes distribute the energy gained by filling of the core hole to multiple electrons. [Preview Abstract] |
Friday, October 23, 2009 11:12AM - 11:24AM |
B1.00007: Search for correlated two electron emission in Auger transition processes Sushant Kalaskar, S.L. Hulbert, R.A. Bartynski, A.H. Weiss Measurements were performed at the National Synchrotron Light Source Brookhaven National Lab, Upton New York, using Auger Photoelectron Coincidence Spectroscopy (APECS) to investigate the physics of Low Energy region of the Auger spectrum. The measurements were carried out on Ag(100) sample, and the spectrum shows a NVV transition related to Ag 4p excitation consisting of a Auger peak accompanied by a substantial low energy region. We selected photon energy of 465eV, energy slightly above the Ag 4p threshold, in order to emphasize the 4p core production compared to all other energy levels. If the Auger transition energy was shared between two and only two electrons we would expect to observe a peak in the I(E) spectrum of the scanned analyzer at an energy of Eauger-Efixed. We performed electron-electron coincidence measurements with one analyzer fixed at 175 eV (half the NVV KE) and the other scanned over the energy range 150 to 200 eV. A possible explanation is that the resulting NVV Auger transition is not shared by 2 but, n number of electrons. This reveals why the LET is smeared into a smooth spectrum as in a single channel photoemission. [Preview Abstract] |
Friday, October 23, 2009 11:24AM - 11:36AM |
B1.00008: Consistent Asymptotic Expansion of Mott's Solution for Oxide Growth Matthew Sears, Wayne Saslow Many relatively thick metal oxide films grow according to what is called the parabolic law $L=\sqrt{2A}t+\dots$. Mott explained this by assuming that ions and electrons are the bulk charge carriers, and that their number fluxes vary as $t^{-1/2}$ at sufficiently long $t$. In this model no charge is present in the bulk, and surface charges were not discussed. It can be thought of as a discharging capacitor, with the oxide surfaces as the plates. However, the theory then is inconsistent because the field decreases, corresponding to discharge, but there is no net current to cause discharge. The present work systematically extends the theory and obtains the discharge current. Because the Planck-Nernst equations are nonlinear (although Gauss's Law and the continuity equations are linear) this leads to a systematic order-by-order expansion in powers of $t^{-1/2}$ for the number currents, concentrations, and electric field during oxide growth. At higher order the bulk develops a non-zero charge density, with a corresponding non-uniform net current, and there are corrections to the electric field and the ion currents. The second order correction to ion current implies a logarithmic term in the thickness of the oxide layer: $L=\sqrt{2A}t+B\ln{t}+\dots$. [Preview Abstract] |
Friday, October 23, 2009 11:36AM - 11:48AM |
B1.00009: Construction and calibration of a low cost X-ray Fluorescence apparatus for compositional analysis of materials Sterling Beeson, David Bixler, Charles Allen, Toni Sauncy X-Ray Fluorescence (XRF) is a useful tool for determining elemental composition of materials. This work involves constructing a fluorescence apparatus using an Eclipse III Tube 30 keV Source with a current of 0-100 $\mu $A and a XR-100CR X-ray detector with DP4 Preamplifier and MCA. The apparatus was constructed from independent components, interfaced for automated data acquisition, calibrated and used to examine a variety of different materials. The characteristic x-rays produced by each element in a sample allow the XRF system to determine the composition along with the percent of each element through the use of a modeling software, XRF-FP. For calibration, known samples (both pure metals and alloys ) were analyzed. A sharp boundary sample was used for spot area calibration. Calibration was followed by the analysis (still ongoing) of zeolite mineral samples of unknown trace-element composition from fifteen sites in the Big Bend area. [Preview Abstract] |
Friday, October 23, 2009 11:48AM - 12:00PM |
B1.00010: Magnetic Texturing of Bi-2212 Superconductor Kyle Damborsky, Peter McIntyre, Nathaniel Pogue Micaceous powders of Bi-2212 can be textured in a magnetic field (aligned with their c axes parallel) utilizing the anomalous normal-state susceptibility. This texturing has the potential to enhance the density and connectivity of multifilament conductors made from such powder, providing the texture can be maintained during conductor fabrication. The magnet lab at Texas A{\&}M University is developing a technique for magnetic texturing and a conductor design to use it to optimum benefit. [Preview Abstract] |
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