Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session B19: Novel Surface Instrumentation and Techniques |
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Sponsoring Units: DCMP Chair: John Wendelken, Oak Ridge National Laboratory Room: Morial Convention Center 211 |
Monday, March 10, 2008 11:15AM - 11:27AM |
B19.00001: Spectromicroscopic characterization of Ag surfaces by energy-filtered LEEM Y. Fujikawa, T. Sakurai, R.M. Tromp Low energy electrons have been applied successfully for both structural and spectroscopic studies since the early days of modern surface science. While the reciprocal space analysis has been combined with both microscopic and spectroscopic studies, there is still very limited availability of spectromicroscopic analysis because it is not easy to achieve both high spatial and spectroscopic resolution at low energies. We present spectromicroscopic characterization of Ag islands on Si substrates using a newly developed energy-filtered Low Energy Electron / Photo-Electron Emission Microscope capable of 5D (2D spatial + 2D reciprocal + energy) surface analysis. The electron energy loss signal from Ag surface plasmons (SP) was imaged in real space with a resolution of 35 nm or less, while the SP energy dispersion was obtained from a 6 $\mu $m diameter area on Ag(111) within $\sim $1 second. HeI photoemission spectra were obtained from a complex Ag island, selecting Ag(111) and Ag(100) areas with a $\phi $4 $\mu $m aperture during PEEM observation. Full dispersion data covering the full reciprocal-energy space were obtained from both surfaces, reflecting their respective symmetries. The ability to perform detailed spectromicroscopic experiments in a standard lab environment is of key importance for nanoscale analysis of novel structures and materials. [Preview Abstract] |
Monday, March 10, 2008 11:27AM - 11:39AM |
B19.00002: Enhanced depth-resolution in multilayer nanostructures from standing-wave excited photoemission Sven Doering, Mihaela Gorgoi, Ruslan Ovsyannikov, See-Hun Yang, Mark Huijben, Franz Schaefers, Daniel Buergler, Claus Schneider, Charles S. Fadley, Walter Braun, Carsten Westphal The depth resolution for studying buried layers and interfaces in multilayer structures with photoemission can be enhanced by exciting with a standing-wave field created by reflection from a multilayer mirror substrate. Combining experiment with x-ray optical simulations can provide information on depth profiles of different chemical species and their magnetic properties. We have applied this method, using both rocking curves and sample scans over a wedge profile, to several types of samples: bare multilayers of Si/Mo and epitaxial SrTiO$_{3}$/La$_{0.7}$Sr$_{0.3}$MnO$_{3}$, and epitaxial MgO on a wedge of Fe on top of a GaAs/AlAs multilayer. Both soft x-ray excitation at the TU Dortmund DELTA facility and hard x-ray excitation at BESSY II in Berlin have been utilized, with the hard x-rays for the first time permitting the study of deeper layers and interfaces. [Preview Abstract] |
Monday, March 10, 2008 11:39AM - 11:51AM |
B19.00003: Interface characterization using atomic core-level shifts Erik Holmstrom, Weine Olovsson, Igor Abrikosov, Anders Niklasson, M. Gorgoi, Olof Karis, Svante Svensson, F. Schafers, W. Braun, G. Ohrwall, G. Andersson, B. Johansson, M. Marcellini, W. Eberhardt We propose a nondestructive technique based on atomic core-level shifts to characterize the interface quality of thin film nanomaterials. Our method uses the inherent sensitivity of the atomic core-level binding energies to their local surroundings in order to probe the layer-resolved binary alloy composition profiles at deeply embedded interfaces. From an analysis based upon high energy x-ray photoemission spectroscopy and density functional theory of a Ni/Cu fcc (100) model system, we demonstrate that this technique is a sensitive tool to characterize the sharpness of a buried interface. We performed controlled interface tuning by gradually approaching the diffusion temperature of the multilayer, which lead to intermixing. We show that core-level spectroscopy directly reflects the changes in the electronic structure of the buried interfaces, which ultimately determines the functionality of the nanosized material. [Preview Abstract] |
Monday, March 10, 2008 11:51AM - 12:03PM |
B19.00004: Manifestation of Work Function Difference in High Order Gundlach Oscillation Chun-Liang Lin, Shin-Ming Lu, Wei-Bin Su, Hwa-Te Shih, Bi-Fen Wu, Yeong-Der Yao, Chia-Seng Chang, Tien-Tzou Tsong Gundlach oscillation (or standing-wave state) is a general phenomenon manifesting in the tunneling spectrum acquired from a metal surface using scanning tunneling spectroscopy. Previous studies relate the energy shift between peaks of the lowest-order Gundlach oscillation observed on the thin film and the metal substrate to the difference in their work functions. By observing Gundlach oscillations on Ag/Au(111), Ag/Cu(111) and Co/Cu(111) systems, we demonstrate that the work function difference is not the energy shift of the lowest order but the ones of higher order where a constant energy shift exhibits. Higher order Gundlach oscillations can thus be applied to determine the work function of thin metal films precisely. [Preview Abstract] |
Monday, March 10, 2008 12:03PM - 12:15PM |
B19.00005: Application of Gundlach Oscillation in Scanning Tunneling Spectroscopy on Nano-Scale Imaging Shin-Ming Lu Gundlach oscillation observed with scanning tunneling spectroscopy (STS) is a phenomenon of field-emission resonance through standing-wave states in the tip-sample gap. No matter if the sample is the thin film or the bulk, peak characteristic of Gundlach oscillation can always appear in the tunneling spectrum. We use STS to study Gundlach oscillation on Ag/Si(111)7$\times $7 and Au(111) surfaces. It is shown that the spectral intensity of the Gundlach oscillation peaks can vary with observed locations. The spatial mappings of spectral intensities at peaks can reveal the contrasts of the interface structure on Ag/Si(111)7$\times $7 and herringbone reconstruction on Au(111) surfaces. The contrast can be attributed to the local variation of the electron transmissivity which affects the transmission background superposing with Gundlach oscillation in the tunneling spectrum. In our observation, the spatial resolution of the mapping is 1 nm and can be preserved even the tip is away from the sample by 60 angstrom. Gundlach oscillation may be useful for the nano-scale imaging of the soft material. [Preview Abstract] |
Monday, March 10, 2008 12:15PM - 12:27PM |
B19.00006: Standing Friedel waves Jun-Qiang Lu, X.-G. Zhang, SokratesT. Pantelides The electron density around defects in a metal is known to exhibit Friedel oscillations. Here, we report simulations that demonstrate a dynamic analogue of the static Friedel oscillation in nanoscale devices. We use a spot gate capacitively coupled to a nanowire or a two-dimensional electron gas, a setup that can be implemented with a sharp STM tip. The application of an AC voltage generates a dynamic standing Friedel wave (SFW), near the spot gate and edges and boundaries. The SFW wave length is controlled by the AC frequency and the device's Fermi velocity, whereby the latter can be measured. The SFW amplitude exhibits resonant behavior at AC frequencies that are related to eigenenergy spacings in the device, allowing their direct measurement. Spin-polarized SFW may be generated in a graphene nanoribbon. [Preview Abstract] |
Monday, March 10, 2008 12:27PM - 12:39PM |
B19.00007: Molecular Etching of Pure and Mn Intercalated TiSe$_{2}$ using an STM Tim Kidd, Brett Gamb, Polina Skirtachenko, Laura Strauss STM is normally a non-destructive technique. However, some materials, such as the transition metal dichalcogenides (TMDCs), are so weakly bonded that STM measurements performed in air can change the surface topology. We performed STM measurements on single crystals of TiSe$_{2}$ and Mn$_{0.05}$TiSe$_{2}$ in air. Under normal scanning conditions, the surface of both TiSe$_{2}$ and Mn$_{0.05}$TiSe$_{2}$ would spontaneously etch, removing single and double molecular layers. In pure TiSe$_{2}$, step edges were unusually rounded and the etching predominately occurred along the scanning direction. In Mn$_{0.05}$TiSe$_{2}$, the etching occurred even more readily. However, step edges in these samples were much straighter, reflecting the crystal symmetry. The symmetry was also seen in the etching of these samples, as triangular pits were often formed along with the usual etching along the scanning direction. The differences seen in the etching of Mn$_{0.05}$TiSe$_{2}$ samples indicate intercalated ions can affect both intra- and inter-layer bond strengths. The etched material disappeared completely from the sample, suggesting that TiSe2 molecules are energized sufficiently to sublimate from the sample. This research indicates that the etching process can be controlled to induce complex nanostructures in the surface of TMDCs. [Preview Abstract] |
Monday, March 10, 2008 12:39PM - 12:51PM |
B19.00008: Effect of Surface Stress on the Stiffness of Cantilever Plates John Sader, Michael Lachut Measurements over the past 30 years have indicated that surface stress can significantly affect the stiffness of microcantilever plates. Several one-dimensional models based on beam theory have been proposed to explain this phenomenon, but are found to be in violation of Newton's third law, in spite of their good agreement with measurements. In this talk, we shall review this work and rigorously examine the effect of surface stress on the stiffness of cantilever plates using a full three-dimensional model. This study establishes the relationship between surface stress and cantilever stiffness, and in so doing elucidates its scaling behavior with cantilever dimensions. Use of short nanoscale cantilevers thus presents the most promising avenue for future investigations. [Preview Abstract] |
Monday, March 10, 2008 12:51PM - 1:03PM |
B19.00009: Direct determination of transient heating in a nanoconfined environment by ultrafast electron diffraction Ryan A. Murdick, Ramani K. Raman, Yoshie Murooka, Richard J. Worhatch, Chong-Yu Ruan Temperature is generally ill-defined at the statistical limit, such as on the ultrashort time scale and in mesoscopic systems. Understanding the thermal energy relaxation and transport at such limits is key to nanoelectronics and energy research. We report on the development of \textit{local} temperature determination on the atomic scale using the technique of ultrafast electron diffraction. Lattice heating characteristics are elucidated by determining the dynamical Debye-Waller factor and local bond stretches, allowing the time scale of electron-phonon coupling and local heating at different length scales to be detailed. We compare these measured temperatures with predictions from two-temperature model (2TM) and determine that strongly coupled `hot' phonons dominate lattice heating at short times (10 ps), and cannot explained by 2TMs. Models beyond the 2TM are developed to explain our data. We also discuss other novel heating scenarios at the statistical limits. [Preview Abstract] |
Monday, March 10, 2008 1:03PM - 1:15PM |
B19.00010: Surface Femtochemistry with Hyperthermal Energy Ion Beams M.P. Ray, R.E. Lake, C.E. Sosolik We are investigating the interactions of hyperthermal energy ions with ultrathin film Schottky diode devices. Specifically, we apply a bias voltage across the device in order to alter the charge transfer dynamics between an incident ion and the metal surface of the Schottky diode. This is an extension of previous work where thermal energy atoms were used to excite electrons-hole pairs and ballistically transport electrons through an ultrathin metal film [1]. In our experiment, we modify the surface electron energy distribution by ballistically transporting electrons to the surface of the thin film. This allows us to tailor the energy level crossings between the incident ion and the metal film and to change the neutralization probability of the scattered beam. Varying the bias voltage will open the possibility for tunable chemical reactions. Preliminary results are presented and discussed in the context of basic ion-surface interactions. [1] H. Nienhaus, H.S. Bergh, B. Gergen, A. Majumdar, W.H. Weinburg and E.W. McFarland, Physical Review Letters \textbf{82}, 446 (1999). [Preview Abstract] |
Monday, March 10, 2008 1:15PM - 1:27PM |
B19.00011: Hyperthermal Energy Ion Scattering as a Time Resolved Probe of Pico- to Femtosecond Surface Excitations R.E. Lake, M.P. Ray, C.E. Sosolik Trajectories of hyperthermal energy alkali ions scattered from single crystal metal surfaces are well described by binary classical collisions with a strong dependence on the atom-surface mass ratio. Such simple events allow hyperthermal ion scattering to be used as a time resolved probe for studying novel surface effects such as femtosecond scale electron transport and ballistic electron excitations. In this talk, three ion scattering cases from the 1-1000 eV energy regime are discussed. K$^{+}$ scattered from Ag(100) is compared to Na$^{+}$ scattered from Cu(100) in terms of interaction potential, image charge effects and neutralization probability. Secondly the heavy atom Cs$^{+}$-Ag(100) system will be presented including a discussion of an anomalous high energy peak possibly attributable to a collective surface response. Finally a method for probing hot electron excitation by an alkali beam scattered from a biased atomically ordered ultrathin film device will be discussed including charge transfer predictions based on rate equations and quantum mechanical 1/N and dynamic matrix renormalization group codes. [Preview Abstract] |
Monday, March 10, 2008 1:27PM - 1:39PM |
B19.00012: An Investigation of Nitride Formation on InP Surface After Nitrogen Ion implantation Mohammad Reza Hantehzadeh The effect of nitrogen ion implantation and change in physical characteristics of InP [100] surface after nitrogen ion implantation is investigated. The energetic 30 KeV nitrogen ions with different doses were implanted into [100] InP surface at about 500-700 k. The formation of different phases of indium nitride and change in surface morphology after the implantation is studied. The annealing effect on change in nitride phase in a nitrogen environment at temperatures above 900 k is observed. The morphology and phases of the surface after ion implantation is characterized using AFM and XRD. [Preview Abstract] |
Monday, March 10, 2008 1:39PM - 1:51PM |
B19.00013: Sputter Deposition System for High Throughput Fabrication of Composition Spread Thin Films John Gregoire, Frank DiSalvo, Hector Abruna, Robert Bruce van Dover We describe a custom built sputtering system that can deposit composition spreads in an effectively UHV environment but which does not require the high-throughput paradigm to be compromised by a long pumpdown each time a target is changed. The system employs four magnetron sputter guns in a cryoshroud (getter sputtering) which allows elements such as Ti and Zr to be deposited with minimal contamination by oxygen or other reactive background gasses. Other features of the deposition system will be presented, most notably the ability to quickly measure deposition profiles from individual deposition sources. We discuss the possibility of calculating codeposited film composition from these profiles, noting that codeposition affords resputtering phenomena which are absent in single-source deposition. To demonstrate the efficacy of this system, we describe our study of combinatorial libraries of electrocatalyst materials for fuel cell applications. This study includes a high-throughput parallel screening of composition spreads using a fluorescence indicator. [Preview Abstract] |
Monday, March 10, 2008 1:51PM - 2:03PM |
B19.00014: Discharging Optics in Vacuum Mark Girard, Dennis Ugolini We have studied using UV illumination to remove excess surface charge from fused silica optics. We commissioned and calibrated a commercial Kelvin probe to measure the surface potential of charged optics in vacuum. Using a Xenon light source and a monochromator, we directed UV light at the sample and were able to remove the excess charge. We determined that the discharging rate scaled linearly with the intensity of the light and the charge density on the surface. By varying the wavelength of the light, we saw a peak discharge rate at 215nm in both uncoated and coated optics. The Kelvin probe also allows us to study the sign of the charge carriers and other techniques for charge removal. [Preview Abstract] |
Monday, March 10, 2008 2:03PM - 2:15PM |
B19.00015: Ordering process in metallic thin films investigated with angle-resolved photoelectron spectroscopy Dah-An Luh, Cheng-Maw Cheng, Chi-Ting Tsai, Ku-Ding Tsuei, Jian-Ming Tang We report the observation of the ordering process in real time of a Ag thin film on a Au(111) surface by measuring the in-plane dispersion of quantum well states using temperature-dependent angle-resolved photoelectron spectroscopy. Low-temperature deposited Ag films on a Au(111) substrate were annealed to yield atomically flat films, and the in-plane dispersion of quantum well states was measured in real time during annealing. Our results revealed that isolated ordered patches, fully crystallized along the surface normal, are formed as an intermediate step in the process of film crystallization. We observed the transition from localized states in a partially ordered film to free-electron-like states in a fully ordered film. This process may be general in many other systems of metal thin films. [Preview Abstract] |
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