Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the Texas Sections of the APS, AAPT, Zone 13 of SPS and the National Society of Hispanic Physicists
Volume 55, Number 11
Thursday–Saturday, October 21–23, 2010; San Antonio, Texas
Session SM5: Condensed Matter |
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Chair: Wilhelmus Geerts, Texas State University Room: University Center III Ballroom I, 1st floor |
Saturday, October 23, 2010 10:00AM - 10:12AM |
SM5.00001: Estimation of the background due to inelastically scattered photoemitted valance band electrons in Ag (100) using APECS S. Kalaskar, S.L. Hulbert, B.R. Bartynski, A.H. Weiss Auger Photoelectron~Coincidence Spectroscopy (APECS) was used to investigate the~Low Energy~tail (LET)~region of the Auger spectrum of Ag(100) sample.~The measurements were carried out~at the National Synchrotron Light Source,~Brookhaven National Lab, and the spectrum shows a NVV transition related to Ag 4p excitation~consisting of a Auger peak accompanied by a substantial low energy region. The fixed energy analyzer~was~set to the Ag 4p core peak and the APECS LET contains the decay features of only that core excitation process.~The spectra contains background due to true coincidences between photoemitted valence band electrons that undergo inelastic scattering and transfer part of their energy with other valence electrons which exit the sample. ~A series of measurements made with the fixed analyzer set at energies 150,160,171 and 175eV above the energy of the core level peak were used to obtain and estimate of this background. The spectrum that results from the subtraction of the estimated background contains significant intensity in the LET region indicating the emission related to Ag 4p core excitation [Preview Abstract] |
Saturday, October 23, 2010 10:12AM - 10:24AM |
SM5.00002: Magneto-Plastic Properties of Ion Beam Sputtered Thin Films on Nitinol Sheet Metal Amanda Gregory, Wilhelmus J. Geerts, Anup Bandyopadhyay Thin magnetic films are used in a variety of applications, and over the course of their lifetimes will likely undergo some degree of plastic deformation. In order to study the ways in which this deformation affects the magnetic properties of thin films, we have deposited films of different thicknesses and compositions on a super-elastic Nitinol substrate and submitted them to varying percentages of strain. The samples were strained using an Instron 5566 materials tester, and a special sample holder was developed to measure the magnetic hysteresis by Vibrating Sample Magnetometer (VSM) in between straining cycles. Our experiments reveal that there is a small process window for which ion beam sputtered thin films do not detach from Nitinol substrates that have undergone up to 5{\%} strain. The sample holder and the magneto-plastic properties of the robust magnetic thin film coatings will be discussed. Additionally, a short video of the straining experiments will be shown. [Preview Abstract] |
Saturday, October 23, 2010 10:24AM - 10:36AM |
SM5.00003: Positron Annihilation Spectroscopy of High Performance Polymer Films under CO$_{2}$ Pressure C.A. Quarles, John R. Klaehn, Eric S. Peterson, Jagoda M. Urban-Klaehn Positron annihilation lifetime and Doppler broadening measurements are reported for six polymer films as a function of carbon dioxide (CO$_{2})$ absolute pressure ranging from 0 to 45 psi. Since the polymer films were thin and did not absorb all positrons, corrections were made in the lifetime analysis for the absorption of positrons in the positron source and sample holder using the Monte Carlo transport code MCNP. Some polymers studied form positronium and others, such as the polyimide structures, do not. For those polymers that form positronium an interpretation in terms of free volume is possible; for those that don't form positronium, further work is needed to determine how best to describe the behavior in terms of the bulk positron annihilation parameters. A few of the studied polymers exhibit changes in positron lifetime and intensity under CO$_{2}$ pressure which may be described by the Henry or Langmuir sorption models, while the positron response of other polymers is rather insensitive to the CO$_{2}$ pressure. The results demonstrate the usefulness of positron annihilation spectroscopy in investigating the sorption of CO$_{2}$ into various polymers. [Preview Abstract] |
Saturday, October 23, 2010 10:36AM - 10:48AM |
SM5.00004: Dependence of calixarene electron beam sensitivity and contrast on functionalization Gregory Spencer, Daniel Ralls, Anup Bandyopadhyay, Michael Blanda Calixarenes form a group of compounds that have been studied as high resolution, high contrast electron beam resists by many groups. They have been shown to be capable of high resolution. While the ultimate resolution may be limited by the size of the calix molecule ($\sim $ 1 nm), both sensitivity and contrast also contribute to their performance. In this study, a particular calixarene molecule has been tested for sensitivity and contrast with differing numbers of attached functional groups. The specific calixarene contained 6 benzene rings and was locked conformationally using bridging xylenyl groups to produce two conformations: a cone conformer and a 1-2-3-alternate conformer. To these calix[6]arenes various numbers of allyl groups were added to improve their electron beam sensitivity. The number of these added groups ranged from 0 to 8 groups. The resulting resists (1{\%} solution with chlorobenzene) were subjected to electron beam exposure. Contrast curves for the cone and alternate conformers were measured by AFM. From this data, both sensitivity and contrast of the resists were found as a function of the number of attached groups. These results and comparison with others will be discussed. [Preview Abstract] |
Saturday, October 23, 2010 10:48AM - 11:00AM |
SM5.00005: Background suppressed measurements of the Low Energy CVV Auger transitions in Cu and Ag(100) K. Shastry, S. Mukherjee Mukherjee, S. Kalaskar, S.L. Hulbert, B.R. Bartynski, A.H. Weiss Low energy Auger lineshapes are difficult to measure because they sit on a large background due to secondary electrons arising from loss processes unrelated to the Auger mechanism. Auger photoelectron coincidence spectroscopy (APECS) was used to the spectrum of the MVV and NVV Auger peaks and associated low energy tails (LETs) in Cu and Ag (100) respectively. The backgrounds due to secondary electrons unrelated to the auger process were suppressed by measuring the Auger spectra in coincidence with the M and N core levels. The APECS measurements reveal a well formed Auger peak at 40 and 60 eV for Cu and Ag respectively accompanied by a significant Auger related intensity in the low energy region. Spectra obtained using APECS are compared with Positron Annihilation Induced Auger Electron Spectroscopy (PAES) measurements which also show a large LET. The LET is discussed in terms of extrinsic mechanisms in which the electrons from the peak lose energy as they propagate to the sample surface and intrinsic mechanisms in which multi- electron auger processes distribute the energy gained by filling of the core hole to multiple electrons.~ [Preview Abstract] |
Saturday, October 23, 2010 11:00AM - 11:12AM |
SM5.00006: Surface Reconstruction of TiO$_{2}$(001) Studied by STM and LEED N.-H. Yu, K.T. Park, Z. Liao, G. Li, X. He, J. Teng, J. Zhang, E.W. Plummer TiO$_{2}$(001) has been investigated by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). After cycles of Ar sputtering and surface annealing at moderate temperatures (up to 600\r{ }C for 15 minutes), TiO$_{2}$(001) reveals the so-called latticework reconstruction: row-like linear structures running along [110] and [1-10] directions. Each row further consists of bright spots separated by 6.5 {\AA}, the lattice constant of the rutile along [110] and [1-10]. In some areas, the rows are separated by 6.5 {\AA} and with the increasing step height of 3 {\AA}, thus forming {\{}111{\}} microfacets. In other areas, the rows are distributed in a more random fashion. Together with LEED, the STM data suggest that the surface reconstruction can be described by added rows of stoichiometric TiO$_{2}$. Further details of the reconstruction model will be presented. [Preview Abstract] |
Saturday, October 23, 2010 11:12AM - 11:24AM |
SM5.00007: Theoretical aspects of studies of high coverage oxidation of the Cu(100) surface using low energy positrons N.G. Fazleev, W.B. Maddox The study of adsorption of oxygen on transition metal surface is important for the understanding of oxidation, heterogeneous catalysis, and metal corrosion. The structures formed on transition metal surfaces vary from simple adlayers of chemisorbed oxygen to oxygen diffusion into the sub-surface region and the formation of oxides. In this work we present the results of an ab-initio investigation of positron surface and bulk states and annihilation probabilities of surface-trapped positrons with relevant core electrons at the oxidized Cu(100) surface under conditions of high oxygen coverage. Calculations are performed for various high coverage missing row structures ranging between 0.50 and 1.50 ML oxygen coverage. Calculations are also performed for the on-surface adsorption of oxygen on the unreconstructed Cu(001) surface for coverages up to one monolayer to use for comparison. The geometry of the surfaces with adsorbed oxygen is fully optimized. Theoretical results are compared with experimental data obtained from studies of oxidation of the Cu(100) surface using positron annihilation induced Auger electron spectroscopy. [Preview Abstract] |
Saturday, October 23, 2010 11:24AM - 11:36AM |
SM5.00008: Residual stress in zinc oxide thin films deposited by atomic layer deposition David Elam, Ramakrishna Kotha, Arturo Ayon, Andrey Chabanov The residual stress in a thin film can have an impact on the electrical and optical properties of the film. In addition, stress is an important consideration when incorporating the material into a microelectromechanical (MEMS) device as large unexpected stresses can cause such a device to fail. The residual stress in ZnO thin films prepared by atomic layer deposition was measured using a radius of curvature technique. The results show relatively low residual stresses on the order of $\sim $0.1 GPa. The stress is observed to change from tensile to compressive as a function of increasing deposition temperature. The polycrystalline structures of the films are also investigated using XRD techniques. [Preview Abstract] |
Saturday, October 23, 2010 11:36AM - 11:48AM |
SM5.00009: The Design and Fabrication of Bismuth Hall Effect Biosensors Anthony Sigillito, Martin Rudolph, Vicki Soghomonian, J.J. Heremans Because of their high sensitivity, accuracy, and low cost, the use of Hall biosensors promises to be an effective diagnostic technique that may aid in the early diagnosis of diseases. In this research, Hall sensors were fabricated from thermally evaporated bismuth thin films. The bismuth films were deposited under high vacuum onto heated Si/SiO$_{2}$ substrates using a two layer deposition technique. The films varied in thickness from 60 nm to 75 nm and were etched into Hall bar geometries using photolithography and wet chemical etching. Magnetoresistance and Hall measurements were taken from 4 K to 300 K. The data indicate that the sensors may be characterized using a two carrier model with high mobility, low density holes and low mobility, high density electrons. Additionally, the sensors were exposed to magnetite nanoparticles and characterized using atomic force microscopy. The results will be reported. This research was funded by the National Science Foundation (NSF Grant DMR-0851662). [Preview Abstract] |
Saturday, October 23, 2010 11:48AM - 12:00PM |
SM5.00010: Using Spectroscopic Ellipsometry to Distinguish Between Si and SiO2 Nanoparticles Justin Frasier, Gregory Spencer, Anup Bandyopadhyay, Wilhelmus Geerts Silicon-based nanoparticles have been synthesized by annealing a thin layer of Si ($\sim $ 10 nm) that was deposited upon thermally-oxidized silicon wafers. Samples were annealed at various temperatures (600 to 900\r{ }C) in UHV and by RTA in flowing Ar to study the particle size distribution dependence on process parameters. Typical particle sizes measured by AFM ranged from 100 to 250 {\AA}. Particle densities up to 50{\%} were observed. Nondestructive spectroscopic ellipsometry was utilized through effective medium approximations (EMA) to determine whether or not the resulting nanoparticles were pure Si, a Si core with oxide shell, or fully oxidized. EMA analysis is based upon the models proposed in the Lorentz-Lorenz (LL), Maxwell-Garnett (MG), and Bruggeman methods. These allow the estimation of the the optical constants (N$_{e})$ of an inhomogeneous material as a weighed average (f) of the optical constants of its constituents (N$_{1}$, N$_{2}$, N$_{h})$. The experimental AFM data and modeling software was used to calculate the optical spectra of the samples assuming various oxidized states of the nanoparticles. The oxidized state of the particles appears to cause distinct features in the optical spectra. The results of these analyses will be discussed. [Preview Abstract] |
Saturday, October 23, 2010 12:00PM - 12:12PM |
SM5.00011: Organization and assembly of microstructures using optical tweezers and in-situ two-photon polymerization Ninad Ingle, Samarendra Mohanty Precise manipulation and organization of objects at microscale using optical tweezers has led to new discoveries in colloidal physics and material science in last two decades. However, long-term stabilization and integration of the optically assembled structures in absence of laser tweezers beam requires precise polymerization of the matrix. Here, we report two-photon polymerization induced assembly of microscopic objects being organized by optical tweezers. A tunable cw Ti: Sapphire laser beam was coupled to the laser port above the epifluorescence port of an inverted microscope in order to trap and organize fluorescence microspheres embedded inside photopolymerizable resin following which the laser beam was modelocked in order to initiate two-photon polymerization. Nanonics Multiview piezo stage enabled controlled scanning of the sample. Further, the laser beam was spatially-structured into an elliptic profile by use of a cylindrical lens in order to trap multiple objects simultaneously and stitch them together with the two-photon polymerization process. Use of such micro-assembled structures in Nanophotonics and cellular manipulation will be presented. [Preview Abstract] |
Saturday, October 23, 2010 12:12PM - 12:24PM |
SM5.00012: An NMR Examination of Synthetic Consolidated Porous Media and Natural Unconsolidated Porous Media Caleb Bahr, Ryan Patterson, Lorne Davis The object of our experiment included using Nuclear Magnetic Resonance (NMR) to find the signal amplitude and relaxation times of our consolidated (solid) samples and to determine topsoil moisture behavior in our unconsolidated (clay and sand) samples. For all of our samples, we found that the experimentally discovered NMR relaxation times represent the pore size of the sample. We also found that the amount of water within the pores is directly proportional to the amplitude of the NMR signal. We also found that NMR relaxation times are proportional to the grain size as well as the pore size of the unconsolidated particles and that the NMR amplitude is not only effected by the amount of water in the pores, but also detects the water within the interstitial spaces of clay granules. [Preview Abstract] |
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