Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S28: Excitations, Scattering and Surfaces of Metals |
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Sponsoring Units: DMP Chair: Randy Fishman, ORNL Room: LACC 506 |
Wednesday, March 23, 2005 2:30PM - 2:42PM |
S28.00001: Quasi-particle corrections to the LSDA+\emph{U} electronic structure of solid bcc hydrogen Emmanouil Kioupakis, Peihong Zhang, Steven G. Louie Quasi-particle calculations within the GW approximation usually start with the LDA electronic structure as mean field solution, which works well for moderately correlated materials. For strongly correlated systems, such as the transition metal oxides, LSDA can give qualitatively wrong ground states, making any further improvement difficult. By starting with the LSDA+\emph{U} mean field results in the GW approximation calculation of the electron self-energy, we expect to have a better understanding of the quasi-particle properties in these systems. We employ this approach in the study of solid hydrogen, a model system for which previous results exist in the literature. This will test the applicability of the technique to more realistic systems. This work was supported by National Science Foundation Grant No. DMR04-39768 and by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy under Contract No. DE-AC03-76SF00098. Computational resources have been provided by NSF at the National Partnership for Advanced Computational Infrastructure (NPACI) and DOE at the National Energy Research Scientific Computing Center (NERSC) [Preview Abstract] |
Wednesday, March 23, 2005 2:42PM - 2:54PM |
S28.00002: {\it Ab initio} calculations of optical spectra M.P. Prange, J.J. Rehr, A.L. Ankudinov We present a real space approach for {\it ab initio} calculations of the optical constants of materials. The approach is based on a generalization of the {\it ab initio} Green's function formalism implemented in the FEFF8 code to include valence and conduction band spectra. This all-electron approach, which is the real-space analog of the KKR method, includes self-consistent potentials, relativistic effects, inelastic losses, self-energy and screened core-hole effects, and multiple-scattering to all orders. Our procedure is based on calculations of the imaginary part of the dielectric function $\epsilon_2$, from which various optical constants can be derived using analytical properties and Kramers-Kronig transforms. Results for several materials are presented and compared with experiment. [Preview Abstract] |
Wednesday, March 23, 2005 2:54PM - 3:06PM |
S28.00003: 1T-TiTe2: scattering rate from infrared and Raman data Lev Gasparov, G. Guentherodt, H.H. Berger, L. Forro, G.G. Margaritondo, D. Tanner The normal-state properties of high temperature superconductors (HTSC) are usually described as those of a non-Fermi liquid, on account of the unusual temperature and frequency dependence of their optical and dc conductivities. This description can be challenged, however, because one has no good example Fermi-liquid (FL) behavior for comparison, especially considering the quasi two-dimensionality of the HTSC. One could address this issue with the help of a reference compound 1T-TiTe$_{2.}$ Both transport and photoemission data on 1T-TaTe$_{2}$ agree well with the Fermi liquid predictions. Thus 1T-TaTe$_{2}$ is believed to be a ``model Fermi liquid''. However, the key signature of the FL is the frequency and temperature dependence of the carrier scattering rate. In this report we discuss our infrared and Raman measurements of the scattering rate in 1T-TiTe$_{2}$ and compare our date to the available photoemission and transport data. $^{\ast }$Supported by Petroleum Research Fund award {\#} 40926-GB10 and Research Corporation Cottrell College science award {\#} cc6130 [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:18PM |
S28.00004: Combined BSE/TDDFT approach for x-ray absorption calculations A.L. Ankudinov, Y. Takimoto, J.J. Rehr Many-body effects such as local fields and the core-hole interaction can be significant in x-ray absorption spectra, even several hundred eV above an absorption edge. The treatment of these effects requires theories that go beyond the independent particle approximation such as the Bethe-Salpeter equation (BSE) or time-dependent density functional theory (TDDFT). However, neither of these approaches is fully satisfactory; the BSE is usually restricted to low energies while the TDDFT ignores non-locality. Here we present a combined TDDFT/BSE approach which is applicable over a wide spectral range. This approach is implemented within a real-space multiple-scattering formalism, with core-hole interaction and the local screening fields calculated within linear response. The approach is illustrated for a several materials and compared with experiment, including the Mg K-edge of MgO, the Ni L-edges, and W M-edges. [Preview Abstract] |
Wednesday, March 23, 2005 3:18PM - 3:30PM |
S28.00005: Multiple-scattering approach to inelastic x-ray scattering calculations J.A. Soininen, A.L. Ankudinov, J.J. Rehr We present an implementation of the real-space multiple-scattering (RSMS) approach for calculations of non-resonant inelastic x-ray scattering (NRIXS) from core-electrons, which is also termed x-ray Raman scattering (XRS). The RSMS approach has been used extensively to model x-ray absorption spectra from deep core levels, including both the fine structure and near-edge behavior. This {\it ab initio} method includes final state self-energy and lifetime effects as well as an approximate treatment of the core-hole interaction. Moreover, the method is applicable to aperiodic or periodic systems alike. The momentum transfer dependence of the XRS is related to the dynamic structure factor $S(\vec q, \omega)$. The results for XRS at different momentum transfers yield information concerning local symmetries of the excited states through changes in the spectral weight of mono-pole, dipole, quadrupole, and higher couplings. Our results are compared both with experiment and with other theoretical calculations. Our near edge calculations are in agreement with previous calculations, and we show how the approach can also be used to calculate the fine structure. [Preview Abstract] |
Wednesday, March 23, 2005 3:30PM - 3:42PM |
S28.00006: Coincidence Measurements of the Auger Cascade Process in Ag R. Sundaramoorthy, A. H. Weiss, S.L. Hulbert, D. Arena, R. A. Bartynski Auger electron spectroscopy provides a probe of many-electron phenomena and the connection between screening, correlation of the final-state holes, and the spectral line shape. Intra-shell and inter-shell hole-hole interactions in the intermediate and final states of the Auger cascade processes shift the measured electron emission spectra of Ag. Here we study the correlation effects of the final state holes created in LMM Auger Cascade process. The final \textit{MM }hole of the \textit{LMM }transition can serve as the initial state for an \textit{MVV }transition, the contribution of which can be separated out from the remaining contributions occurring from other cascades such as LMV and the direct transition using Auger-Auger coincidence spectroscopy. Here we present results for the x-ray excited Auger \textit{MVV }spectra of Ag measured with synchrotron radiation excitation where we study the difference between the MVV -- 2p3/2 Auger photoelectron coincidence spectra and the LMM-MVV Auger-Auger coincidence spectra. The observed differences throw light on the correlation effects in many core-hole excited states. [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 3:54PM |
S28.00007: Interaction between a surface plasmon and surface nano-defects in thin metallic films. Ra\'{u}l Garc\'{i}a-Llamas, Javier Dur\'{a}n-Favela, Jorge Gaspar-Armenta, Jos\'{e} Valenzuela-Benavides The intensity of the electromagnetic near-field produced by the interaction between surface plasmons and surface nano-defects on otherwise planar structure is studied theoretically. The structure is a thin metallic film bounded by glass and vacuum, the Kretchmman configuration used for the excitation of surface plasmons. Exact and perturbation solutions, until fourth order in the surface defect profile, of the reduced Rayleigh equation are found to obtain the intensity. The numerical results are calculated using a single or double Gaussian wells, and triangular shaped one. Rapid oscillations of the near field are found whose period is the inverse of two times the mode propagation constant. A Fourier Transform technique is used to reconstruct the surface defect profile from the near-field intensity obtained at constant height. [Preview Abstract] |
Wednesday, March 23, 2005 3:54PM - 4:06PM |
S28.00008: Spectral response of the optical second-harmonic scattering from a metallic cylinder Jesus Maytorena, Claudio Valencia We study the scattering of second-harmonic (SH) radiation generated by an infinite cylinder of homogeneous, isotropic, centrosymmetric material and arbitrary radius illuminated perpendicularly to its axis with $p-$ or $s-$ polarized light. We derive analytical expressions for the SH radiated field and illustrate the theory for a simple metal cylinder. The nonlinear source polarization includes both a nonlocal bulk term and a dipole-allowed surface term which corresponds to the interfacial region where the inversion symmetry is broken. We consider the cylinder as locally flat and use the dipolar surface susceptibility resulting from a microscopic calculation based on the density functional formalism for a planar jellium surface. The frequency dependence of this surface contribution manifests itself in the spectral response. The calculated SH scattering cross section shows a separated peak corresponding to a surface-intrinsic collective mode in addition to peaks due to plasmon modes of the cylinder whose frequencies are determined by the linear optical properties at either fundamental or SH frequency. [Preview Abstract] |
Wednesday, March 23, 2005 4:06PM - 4:18PM |
S28.00009: Observation of growth mode dependence on over-potential values: a combination of in-situ optical monitoring and ex-situ atomic force microscopy characterization. M. K. O'Toole, J. Gray, T. Moffat, C. Orme, W. Schwarzacher, X.D. Zhu We study the over-potential electrodeposition of Pb on Cu(100) using a combination of an \textit{in-situ} oblique-incidence reflectivity difference technique and \textit{ex-situ} atomic force microscopy. We identified two distinctly different over-potential growth modes that depend on the values of the overpotential. We have characterized the morphology corresponding to the two growth modes using AFM. At a high over-potential there is even growth of small clusters across the monolayer thick under-potential deposited (UPD) Pb covered Cu(100) surface. At lower over-potentials (a fraction of a volt from the value for UPD), we observed much larger 3-D clusters, more than 400 nm in height and separated by an averaged distance of one micron. [Preview Abstract] |
Wednesday, March 23, 2005 4:18PM - 4:30PM |
S28.00010: Determining Film Thickness and Probing Buried Interface Structure with Characteristic Scanning Tunneling Spectroscopy Shin-Ming Lu, W.B. Su, C.L. Jiang, H.T. Shih, C.S. Chang, Tien T. Tsong Structural and electronic properties of atomic-scale flat Ag films grown on Si (111)-7×7 are measured with scanning tunneling microscopy and spectroscopy. Spectroscopy for each film thickness not only reveals the features of transmission resonance and distinct quantized bound states, but can also probes the buried interface structure. First, the energy levels of those states vary with the film thickness and can serve as the fingerprints. The film thickness can thus be determined with the characteristic spectrum, which is especially useful as the film covers the entire substrate. Secondly, the spectra manifest a shift of electronic resonance and quantized bound states due to varied reflection strength at the buried interface. With this effect, the buried interface structure can be probed. [Preview Abstract] |
Wednesday, March 23, 2005 4:30PM - 4:42PM |
S28.00011: Persistent Step-Flow Growth of Strained Overlayers on Vicinal Substrates Wei Hong, Mina Yoon, Zhigang Suo, Ho Nyung Lee, Hans M. Christen, Doug H. Lowndes, Zhenyu Zhang Driven by step-step (SS) attraction, a strained overlayer grown on a vicinal substrate is inherently unstable, as manifested by step bunching. The step-edge (or Ehrlich-Schwoebel) barrier effects may either accelerate, delay, or suppress step bunching, depending on the nature of the ES barriers for a given system. Using linear stability theory and numerical simulations, we analyze the morphological evolution in heteroepitaxial growth with explicit consideration of the competition between the SS and ES effects. We establish the existence of a deposition flux window within which stable and persistent step-flow growth can be achieved. This window for step-flow growth is sandwiched between the island growth mode at too high deposition fluxes, and the step bunching mode at too low deposition fluxes. We express the phase boundaries in terms of intrinsic physical parameters and experimentally controllable growth conditions, and compare the predictions with experimental results from PLD growth studies of metal oxide thin films. [Preview Abstract] |
Wednesday, March 23, 2005 4:42PM - 4:54PM |
S28.00012: Surface Relaxation of V(100); Experiments and Ab-Initio Calculations: a status report on the Feibelman Issue D. Lacina, A. Ciucivara, B.R. Sahu, L. Kleinman, J.L. Erskine Systematic discrepancies between first-principles calculations and experimental determinations of the surface relaxation of reactive transition metals was first noted by Feibelman.$^{[1]} $ The basic issue is that calculations invariably yield first- layer (inward) relaxations that substantially exceed the results obtained by electron diffraction, and the disagreement lies beyond the accepted accuracy of the experiments and calculations. We report new LEED results and calculations for V (100) that explore this trend and present a status report on the primary issues. The LEED results for several data sets at 300 K and 100 K are robust and consistent with d$_{12}$ = -5.0 \underline{+}1.0 \% and d$_{23}$ = 3.6 \underline{+}1.0 \%with acceptable Pendry and Zanazzi-Jona r-ractors. Preliminary calculations using pseudopotentials without partial core corrections gave d$_{12}$ = -14.0 \% in the GGA (cf. the more accurate FPLAPW d$_{12}$ = -11.1 \%).$^{[2]}$ Meta-GGA$^{[3]}$ calculations resulted in d$_{12}$ = -12.0 \% suggesting meta- GGA FPLAPW calculations might yield d$_{12}$ as small as -9 \%, still an unacceptably large deviation from experiment. \newline Supported by the R.A. Welch Foundation \newline 1. P.J. Feibelman, Surf. Sci. \underline{360}, 297(1996) \newline 2. G. Bihlmayer, T. Asada, and S. Blugel, Phys. Rev. B\underline{62}, 11937(2000) \newline 3. V.N. Starorerov, et al., Phys. Rev. B\underline{69},75102(2004) [Preview Abstract] |
Wednesday, March 23, 2005 4:54PM - 5:06PM |
S28.00013: Theory of Current Crowding Effect on Electromigration Lingyun Zhang, King-Ning Tu We investigate the current crowding in the inhomogeneous area and explore the mechanism of gradient force in electromigration. The inhomogeneous field, which is stimulated by the inhomogeneous current density, can provide a force for the vacancies. It is shown that the magnitude of the force along the normal direction of current density is the same order as the electric field force. By using the self-consistent approach, the distribution of electrons and vacancies, and the current density distribution can be obtained. The detailed calculation demonstrates that the current density gradient is a driving force and induces the atomic rearrangement in the inhomogeneous area, which explain why the void can be formed in the low current density regions of an interconnect. Furthermore, the quantum mechanical approach is developed to understand the nature of gradient force in electromigration. [Preview Abstract] |
Wednesday, March 23, 2005 5:06PM - 5:18PM |
S28.00014: The Ni(111) surface electrons investigated with low-temperature scanning tunneling spectroscopy Kai-Felix Braun, C.F.J. Flipse, K.-H. Rieder The electronic structure of the ferromagnetic Ni(111) surface has been attracting interest for a long time. Despite experimental and theoretical effort, reported values of binding energies, effective masses and number of the surface states and surface resonances differed substantially. Working with a local probe technique reveals relevant contributions from adsorbates and defects. Here we present an extensive scanning tunneling microscopy and spectroscopy investigation at low temperature, employing fourier transform methods for the analysis. The results show a parabolic surface state with an upward dispersion at --165 meV with a surprisingly low effective mass of 0.17 m$_{e}$ and a downward dispersing surface resonance at --230 meV. From the decay of the standing wave pattern at step edges electron and hole lifetimes have been determined with values considerably smaller than found on noble metal surfaces. Details of the surface electronic structure have been revealed including an anti-resonance at the Fermi energy. [Preview Abstract] |
Wednesday, March 23, 2005 5:18PM - 5:30PM |
S28.00015: Optimal Switching Time Israel Klich, Leonid Levitov We discuss the noise produced in the process of switching mesoscopic conductors between two noiseless states: perfectly connected and disconnected, in the presence of a bias voltage V. We show that there are two main contributions to the noise: a switching noise logarithmic in the time of observation T, and a quantum shot noise accumulated during the process of switching and proportional to V, this leads to a minimization problem for the optimal switching time. Switching noise is expected to be a fundamental parameter in nano-circuits. We also discuss the relation of this result to an estimation of entangelment entropy of a Fermi sea. [Preview Abstract] |
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S28.00016: Surface, Step-Edge, and Facet-Edge Diffusion Barriers in Growth of Pb Nanomesas Yong Han, Feng Liu, Guang-Hong Lu, Byeong-Joo Lee To obtain a better understanding of the growth kinetics of faceted Pb mesas on Si(111) surface, we perform extensive calculations of diffusion barriers for a Pb adatom (1) on a flat Pb(111) surface, (2) crossing a single A- or B-step edge on the Pb(111) surface, and (3) crossing the joint edge of the Pb(111) and (001) facet, using a modified embedded atom method. We have investigated different diffusion mechanisms mediated by vacancies and concerted displacements of multiple atoms. A quantitative comparison will be made between the calculated results and recent experiments. *This work is supported by NSF. [Preview Abstract] |
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