Bulletin of the American Physical Society
2006 Texas Section of the APS Joint Fall Meeting
Thursday–Saturday, October 5–7, 2006; Arlington, Texas
Session CMP3: Condensed Matter III |
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Chair: Howard Richards, Texas A&M Commerce Room: UT Arlington, University Center Concho |
Saturday, October 7, 2006 10:30AM - 10:42AM |
CMP3.00001: Interaction of Hafnium oxide with silicon Richard Miller, A.R. Chourasia X-ray photoelectron spectroscopy has been employed to study the interaction of hafnium oxide with silicon. Hafnium was deposited in an oxygen atmosphere onto silicon substrates kept at temperatures: 20$^{\circ}$C, 100$^{\circ}$C, 200$^{\circ}$C, 300$^{\circ}$C, 400$^{\circ}$C, and 500$^{\circ}$C. The evaporation was done by the e-beam technique. The 3d and 4f core levels and the X-ray excited Auger regions of hafnium were recorded using the zirconium L$_{\alpha }$ radiation. The Auger parameter was determined from these spectra. The Wagner plot was constructed using the Auger parameter values. This plot showed a shift in the parameter from room temperature to high temperature. The data for 100$^{\circ}$C, 200$^{\circ}$C, 300$^{\circ}$C, and 400$^{\circ}$C showed no changes. This has been interpreted as no change in the stoichiometry of the hafnium oxide deposited on the silicon substrate. The 500$^{\circ}$C sample shows a significant change indicating change in the environment of hafnium. At this temperature silicon is observed to remove some oxygen from hafnium oxide to form silicon oxide. The change in the Auger parameter has been interpreted as due to stress at the hafnium oxide/silicon interface. [Preview Abstract] |
Saturday, October 7, 2006 10:42AM - 10:54AM |
CMP3.00002: An \textit{Ab Initio }Full Potential Fully Relativistic Study of Atomic Carbon, Nitrogen, and Oxygen Chemisorption on the (111) Surface of $\delta $-Pu Raymond Atta-Fynn, Asok Ray Fully-relativistic full potential density functional calculations have been performed to investigate atomic carbon, nitrogen, and oxygen chemisorption on the (111) surface of $\delta $-Pu using the all-electron linearized augmented plane wave plus local orbitals code WIEN2k and the generalized gradient approximation to density functional theory. The surface was modeled by a three-layer periodic slab separated by 60 Bohr vacuum with two atoms per surface unit cell. The hollow fcc adsorption site was found to be the most preferred site with chemisorption energies of 6.539 eV, 6.714 eV, and 8.2 eV for the C, N, and O adatoms, respectively. The respective distances of the C, N, and O adatoms from the surface were found to be 1.16 {\AA}, 1.08 {\AA}, and 1.25 {\AA}. Analysis of the partial charges inside the atomic spheres, charge density distributions, and the local density of states indicate hybridizations between Pu 5f and the 2p states of the adatoms. [Preview Abstract] |
Saturday, October 7, 2006 10:54AM - 11:06AM |
CMP3.00003: Maximal Violation of the Two-Step Model of Auger Decay in Auger Cascade Processes Rajalakshmi Sundaramoorthy, Alex Weiss, Steven Hulbert, Robert Bartynski The two step model assumes Auger decay processes to be independent of the manner of the creation of the initial core hole and that the screening time is short compared to the core-hole life time. Auger-Photoelectron Spectroscopy(APECS) and Auger-Auger Coincidence Spectroscopy (AACS) were used to show that the spectra associated with Mn MVV transitions in which the initial M core hole was created by a prior LMM Auger transition is much wider that the spectra associated with MVV transitions in which the M hole was created by direct photoemission. The increased energy width of the MVV transitions that follow LMM decays strongly suggests the involvement of valence hole(s) created in the prior cascade step that have not been filled at the time of the subsequent Auger decay thus violating the two-step model. The energetics of the Auger cascade processes is modeled in terms of correlation integral(s) and convolution integral(s) over the valence band density of states. Comparisons with recent Auger-Auger Coincidence studies of Ag and Pd will be made. [Preview Abstract] |
Saturday, October 7, 2006 11:06AM - 11:18AM |
CMP3.00004: Electronic and vibrational properties of the Na$_{16}$Rb$_{8}$Si$_{136}$ and K$_{16}$Rb$_{8}$Si$_{136}$ clathrates Koushik Biswas, Charles W. Myles We have studied the electronic and vibrational properties of the Na$_{16}$Rb$_{8}$Si$_{136 }$and K$_{16}$Rb$_{8}$Si$_{136}$ clathrate compounds using first principles calculations. In qualitative agreement with the rigid-band model, the electronic band structures display no major modifications due to the inclusion of the alkali metal guests. The guest atom valence electrons occupy the Si$_{136}$ conduction band states, resulting in a shift of the Fermi level into the conduction band of the ``parent'' Si$_{136}$ framework. Unlike pristine Si$_{136}$, the electronic density of states of the filled clathrates show two sharply peaked structures and a dip near the Fermi level. This feature may help to qualitatively explain the temperature-dependent Knight shift observed for the NMR active nuclei in Na$_{16}$Rb$_{8}$Si$_{136}$.\footnote{S. Latturner, B. B. Iversen, J. Sepa, V. Srdanov, and G. Stucky, Phys. Rev B 63, 125403 (2001).} The phonon dispersion curves for the filled clathrates reveal low frequency, localized ``rattling'' modes for the Na (or K) and Rb guest atoms. These flat rattler modes compress the highly dispersive host acoustic mode band width. As a consequence, the rattler modes may efficiently scatter the heat-carrying host acoustic phonons, potentially suppressing the lattice thermal conductivity. [Preview Abstract] |
Saturday, October 7, 2006 11:18AM - 11:30AM |
CMP3.00005: Image-potential surface states and positron annihilation characteristics at the reconstructed Si(100)-(2$\times $1) and Si(100)-p(2$\times $2) surfaces. N.G. Fazleev, J.L. Fry, A.H. Weiss Positron probes of semiconductor surfaces are capable to non-destructively provide information that is both unique to the probe and complimentary to that extracted using other more standard techniques. In this talk the results of theoretical studies of positron surface states and annihilation characteristics of surface trapped positrons at the Si(100) surface are presented. Calculations are performed for the Si(100) surface with (2$\times $1) and p(2$\times $2) reconstructions. The orientation-dependent variations of the atomic density and electron density are found to affect the localization of the positron surface state wave function at the reconstructed surface. It is shown that the positron surface state wave function extends into the lattice in the regions where atoms are displaced from their ideal terminated positions due to reconstructions. Estimates of the positron binding energy and annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of Si. The computed core annihilation probabilities are compared with the results of studies of Si(100) using Positron Annihilation Induced Auger Electron Spectroscopy (PAES). The sensitivity of annihilation probabilities to crystal face indicates that PAES could serve as an important surface diagnostic tool capable of distinguishing different semiconductor surfaces and defining their state of reconstruction. [Preview Abstract] |
Saturday, October 7, 2006 11:30AM - 11:42AM |
CMP3.00006: A FP-LAPW Study of Atomic Carbon, Nitrogen, and Oxygen Chemisorption on the (100) Surface of $\delta $-Pu Raymond Atta-Fynn, Asok Ray Fully relativistic full potential density functional calculations have been performed to investigate atomic carbon, nitrogen, and oxygen chemisorption on the (100) surface of $\delta $-Pu using the all-electron augmented plane waves plus local basis code WIEN2k. The surface was modeled by a three-layer periodic slab with two atoms per surface unit cell. The center adsorption site is found to be the most preferred site with chemisorption energies of 7.964 eV, 7.665 eV, and 8.335 eV for the C, N, and O adatoms, respectively. The corresponding optimized distances of the adatoms from the surface are found to be 0.26 {\AA}, 0.35 {\AA}, and 0.48 {\AA}. The work functions and the net magnet moments respectively increased and decreased in all cases compared with the bare $\delta $-Pu (100) surface. Analysis of partial charges inside the atomic spheres, charge density distributions, and the local density of states have been performed to investigate the nature of the interaction between the surface Pu atoms and the adatoms. [Preview Abstract] |
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