Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session U23: Low-D Metals and Responses |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Rongying Jin, Oak Ridge National Laboratory Room: Colorado Convention Center 110 |
Thursday, March 8, 2007 8:00AM - 8:12AM |
U23.00001: Internal friction of a one micron thick silver film between 1 mK and 1 K Andrew Fefferman, R. O. Pohl, J. M. Parpia Metal films are useful for thermalization and electrostatic actuation of both macroscopic and nanoscale oscillators at low temperatures. However, the effect of the metal film on the dynamics of the oscillator substrate is not always known since previous measurements of the internal friction $Q^{-1}$ of metal films extend down down to a few hundred mK. Measurements of X. Liu $\it{et~al}$ [Phys. Rev. B $\bf{59}$, 11767 (1999)] showed that between 0.5 and 1 K many micron-thick metal films exhibit a $Q^{-1}$ plateau at the level of several $10^{-4}$, but the existence of the plateau below 500 mK was unknown. We have measured $Q^{-1}$ of a one micron thick silver film between 1 mK and 1 K using a single crystal silicon double paddle oscillator substrate vibrating at 5.5 kHz. $Q^{-1}$ of the substrate was measured prior to deposition of the film so that $Q^{-1}$ of the film alone could be extracted from measurements of the composite oscillator. $Q^{-1}$ of the silver film was nearly constant at $4 \times 10^{-5}$ between 1 and 10 mK and increased to $10^{-4}$ as temperature increased from 10 mK to 1 K. These data will be valuable for future experiments on metal coated silicon or silicon nitride resonators at mK temperatures. [Preview Abstract] |
Thursday, March 8, 2007 8:12AM - 8:24AM |
U23.00002: Thermal Expansion and Specific Heat of some BeCu Alloys J.C. Cooley, J.C. Lashley, T.J. Tucker, W.L. Hults, S.J. Tracy, G.M. Schmiedeshoff We have measured the specific heat and thermal expansion of some polycrystalline BeCu alloys with an atomic concentration of Cu up to 3{\%}. We will present and discuss our measurements in the context of a Gruneisen analysis. [Preview Abstract] |
Thursday, March 8, 2007 8:24AM - 8:36AM |
U23.00003: Optical properties of Al at shock-melt conditions Lorin X. Benedict, John E. Klepeis We report calculations of the linear optical absorption spectra of aluminum at pressures of roughly 1 Mbar and temperatures of around 5000 K. Both the hot fcc solid and the liquid have been studied at those conditions, and we conclude that it should be possible to distinguish solid from liquid when Al has been shocked. This suggests that in situ measurements of optical constants may serve as a diagnostic for melting in dynamic high pressure experiments. Calculations were performed using a combination of ab initio and semi-empirical electronic structure schemes, together with a combination of molecular dynamics schemes to generate snapshots of hot solid and liquid ionic configurations. Lower densities and temperatures were considered as well, showing favorable comparison with ambient pressure high-T optical measurements on Al. [Preview Abstract] |
Thursday, March 8, 2007 8:36AM - 8:48AM |
U23.00004: Ultrafast Extreme Ultraviolet Holography: Dynamic Measurement of Surface Deformation Mark Siemens, Oren Cohen, Qing Li, Margaret Murnane, Henry Kapteyn, Ra'anan Tobey, Keith Nelson We demonstrate femtosecond time-resolved dynamic holography using coherent extreme ultraviolet (EUV) light generated by high harmonic upconversion of a femtosecond laser. We use a novel excitation geometry in which a pump laser excites a narrow line on the sample, and a much larger EUV beam probes the perturbed sample. The unperturbed portion of the sample reflects the EUV beam to serve as the reference beam, while the pumped region diffracts the EUV probe to from the object beam. The interference of the two beams forms a dynamic hologram that changes as the surface relaxes. By varying the pump-probe delay time, we observe laser-induced surface displacement and subsequent acoustic oscillations in thin metal films. EUV probing in this manner has sub-picometer sensitivity to vertical surface deformation, and is largely free of ambiguities associated with electronic and photoelastic effects that complicate other photoacoustic schemes. In the future, we will extend phase-sensitive detection to study other transient dynamics, such as thermal transport in nanostructures. [Preview Abstract] |
Thursday, March 8, 2007 8:48AM - 9:00AM |
U23.00005: Resonant mapping of image states on metal surfaces using tunable femtosecond light Kevin Knox, Mehmet Yilmaz, Nader Zaki, Jerry Dadap, Richard Osgood, Peter Johnson We report resonant band mapping using angle-resolved two-photon photoemission measurements of image states on Cu(111) surfaces using a tunable ultrafast femtosecond optical parametric amplifier source. An optical parametrically amplified visible beam is frequency doubled to obtain a tunable fs UV source with photon energies in the 3.6 to 5 eV range. Unoccupied image states are populated by resonant excitation from the occupied sp-like surface state of Cu(111). The image state electrons are then probed by absorption of a second photon of the same energy. Since the surface and image states have different effective masses, resonant excitation occurs at different parallel momenta for each photon energy. By tuning the photon energy we are able to resonantly map both the surface and image state spectra. Our fs laser provides high signal to noise ratio and ultrafast time resolution and the resonant mapping scheme allows for precise measurement of the dispersion and reference planes (the dispersion minimum) of the occupied and excited bands. [Preview Abstract] |
Thursday, March 8, 2007 9:00AM - 9:12AM |
U23.00006: Scattering of an Incident Beam by a Magnetic Structure using FDTD. Miguel A. Alvarez-Cabanillas The electromagnetic scattering by a magnetic structure is modeled using finite difference time domain (FDTD). The electromagnetic wave with normal incidence to the magnetic structure has a plane wave front. The incident electric field is chosen perpendicular to the magnetization in the magnetic structure. The electric field is rotated by the magneto-optical Kerr effect (MOKE) and then reflected. This phenomenon is simulated by building the algorithm for FDTD from the Maxwell's equations, using a Transversal Magnetic distribution of the fields in the numerical mesh. The MOKE is introduced in the dielectric constant of the magnetic material. The space of simulation is surrounded by an absorbing boundary condition (ABC). The Perfect Match Layer (PML) was chosen as an ABC with ten layers, enough to reduce the reflected wave. The same size of cells were used in the while mesh. The size of the cells in the space of simulation and the time step were selected in agreement to reduce the numerical dispersion and avoid numerical instability. The algorithm simulates the correct rotation of the electric field as was predicted by MOKE. The numerical results of the FDTD were compared with the analytic solution in order to verify the algorithm and validate the numerical results. [Preview Abstract] |
Thursday, March 8, 2007 9:12AM - 9:24AM |
U23.00007: Measurement of the resonance shift in the radar backscattering cross section of thick stainless steel fibers at 35 GHz Sharhabeel Alyones, Charles Bruce Measurements of the radar backscattering cross section of stainless steel fibers with low length-to-diameter ratio (thick fibers) had been done at 35 GHz. The intention was to confirm the resonance shift in length predicted by a numerical solution of the general problem of electromagnetic scattering and absorption by finite conducting wires [1]. The numerical methods solves the generalized form of the Pocklington equation, which is valid for both thin and thick fibers. Single particle radar backscattering measurement system was used and the resonance shift had been confirmed for four sets of aspect ratios. The position of the first resonance is shifted to shorter lengths in comparison with the previous analytical solution of the problem by P. Watermann and J. Pedersen [2]. \newline [1] Sharhabeel Alyones, Charles W. Bruce, and Andrei Buin$, `` $Numerical methods for solving the problem of electromagnetic scattering by a finite thin conducting wire$'', $ accepted for publication in\textit{ IEEE. Trans. Antennas and Propag.} \newline [2] P. C. Waterman, ``Scattering, absorption and extinction by thin fibers,'' Accepted for publication in \textit{J. Opt. Soc. A.} [Preview Abstract] |
Thursday, March 8, 2007 9:24AM - 9:36AM |
U23.00008: ABSTRACT WITHDRAWN |
Thursday, March 8, 2007 9:36AM - 9:48AM |
U23.00009: Plasmon Vibrational Delocalization in 1D Disordered Wigner Lattices Shimul Akhanjee, Joseph Rudnick We explore various aspects of classical 1D Wigner solids in the presence of strong disorder at $T=0$. Two different realizations of electrostatic randomness are studied: a system of particles with spatially random charge strengths and a system of like charges interacting with an external random potential. In the random potential system we have discovered a novel type of vibrational delocalization transition of the plasma oscillations. Finite size scaling studies of the localization length and inverse participation ratio reveal an Anderson transition from extended to localized eigenmodes at larger eigenfrequencies. Other properties of the eigenmodes are also discussed in the context of this criticality. Additionally, for both models the probability density of particle spacings is examined analytically through the use of probability convolutions within a weak disorder approximation and compared to numerically relaxed ensembles. We find that the statistical configuration of the charges is sensitive to the to the specific type of quenched random distribution. [Preview Abstract] |
Thursday, March 8, 2007 9:48AM - 10:00AM |
U23.00010: Evidence of Electron-Plasmon Coupling in Single Crystal Bismuth Riccardo Tediosi, N. Peter Armitage, Enrico Giannini, Dirk van der Marel We present a detailed optical study via the extended-Drude model analysis of single crystal bismuth using infrared reflectivity and visible-light ellipsometry. The extremely narrow Drude peak and the small value of the screened plasma frequency are consistent with the small carriers density typical for this semimetallic system. The temperature dependence of the optical properties is dominated on one side by the progressive narrowing of the free electron Drude peak and on the other side by the progressive appearance of an absorption peak in the region between the itra-band and inter-band contributions with a consequent change in the frequency dependent scattering rate $\tau^{-1}(\omega)$. We observed that the inflection point $\omega_{\tau}(T)$ corresponding to the increase of $\tau^{-1}(\omega, T)$ closely follows the change of the plasma frequency with temperature according to the relation $\omega_{\tau}(T) \simeq \omega_p(T)$. This aspect suggests a possible interaction between free electrons and collective modes as already theoretically demonstarted in earlier works. In this scenario we calculated the scattering rate contribution for electron-plasmon interaction starting from the plasmon dispersion relation observing an astonishing good agreement between experimental result and theoretical expectation. [Preview Abstract] |
Thursday, March 8, 2007 10:00AM - 10:12AM |
U23.00011: Electromagnetic Contribution to Enhanced Raman Scattering from a Metal Nanoshell Dimer Ke Zhao, Zhenyu Zhang We present a theoretical framework for calculating the electromagnetic contribution to enhanced Raman scattering from a metal nanoshell dimer, using time dependent local density approximation within density functional theory, and going beyond existing dipole excitation treatments. When applied numerically to silver and gold nanoshell dimers, we obtain results that can be compared with those derived from classical electrodynamics, which in turn allows to test the validity of using local dielectric functions to describe nanoshell dimers. [Preview Abstract] |
Thursday, March 8, 2007 10:12AM - 10:24AM |
U23.00012: Convective Atom Transport as a Modifier of Near-Surface Alloy Composition Yong W. Kim Thermophysical properties of metallic alloys are manifestly the features of a given material specimen, and, as such, they are dependent on their elemental composition. Some properties are measured at surfaces and others are measured through the bulk as a whole. Complications arise when the elemental composition becomes position dependent within a material specimen. Such occurrences turn out to be common and have been demonstrated by simultaneous measurements of thermal diffusivity and elemental composition by time-resolved spectroscopy of laser-produced plasma (LPP) plume emissions. To further understand the cause, we have investigated the evolution of near-surface composition of Wood's alloy (composed of 50 W{\%} bismuth, 25W{\%} lead, 12.5 W{\%} tin and 12.5W{\%} cadmium) as a model system under the influence of thermal cycling with, and without, temperature gradient over the specimen. Surface composition modification has been found to take place by accumulation of irregularly spaced gray patches of inhomogeneous composition on the surface in the presence of temperature gradient. Surface position and depth-resolved determination of elemental composition by LPP spectroscopy has revealed fully 3-D composition structures of the patches. Candidate mechanisms will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 10:24AM - 10:36AM |
U23.00013: Effects of Zr Doping on the Oxidation of Low-index Crystal Surfaces of Single Crystal beta-Nickel Aluminum Serif Uran, Marcos Grimsditch, Boyd Veal, Paul Paulikas Addition of small amount ($\sim $0.1 atm {\%}) of a reactive element (e.g., Y, Zr, Hf) to substrate alloy prior to oxidation is known to improve the oxidation properties (i.e., adherence) of these alloys. This phenomenon is known as the reactive element effect. The purpose of this investigation is to determine the role of reactive element doping during oxidation of a single crystal. It can be argued that absence of grain boundaries in the underlying metal might change or inhibit the improved scale adherence normally produced by doping with a reactive element. By comparing the effects of reactive element doping on the oxidation of different crystallographic faces, we expect to improve our understanding of this still very poorly understood phenomenon. In this study, we have measured scale thickness, composition and residual stress as a function of oxidation temperature for the three principal low-index surfaces (001), (1-10) and (111) of zirconium doped specimen. Systematic differences are observed among different surfaces and the results are compared to those of the undoped crystal. [Preview Abstract] |
Thursday, March 8, 2007 10:36AM - 10:48AM |
U23.00014: Electronic structure of ultrathin films of Co on Cu(775) stepped surfaces using high-resolution photoemission spectroscopy Shancai Wang, Jerry Dadap, Mehmet Yilmaz, Kevin Knox, Nader Zaki, Richard Osgood, Tonica Valla, Peter Johnson We perform high-resolution photoemission spectroscopy, using the U13UB UV line at the NSLS, to study the electronic structure of bare and low-coverage Co on Cu(775) stepped surfaces. Despite the relatively wide terrace widths, the bare surface shows clear evidence of umklapps due to the step edges; this behavior is sharpened in the presence of very low Co coverage due to step pinning. We also measure the dispersion for electron emission along and perpendicular to the steps and obtain an exchange splitting energy for the lower Co d-bands at 16 and 25 eV photon energies. The splitting energy reaches a value of as low as $\sim $0.4 eV, which is considerably smaller than that obtained for both Co and Co/Cu(111) surfaces. In addition, the typical widths of the spin states are larger than those obtained for the other surfaces, indicating the increased scattering channels arising from the strong influence of the steps. [Preview Abstract] |
Thursday, March 8, 2007 10:48AM - 11:00AM |
U23.00015: Oxidation of Pt (100) surface: Ab initio studies Eunja Kim, David Stucke, Tao Pang We have performed density-functional calculations to investigate the oxidation process of Pt (100) surface. We carefully examine the previously proposed models and propose a new dissociative model of oxygen molecules on the Pt (100) in this study. Our findings also indicate that one monolayer of oxygen atoms can be covered on Pt (100) surface with 1.09 eV/O$_2$. The role played by oxygen and temperature in the degradation of catalyst will be further discussed in details. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700