Bulletin of the American Physical Society
12th Annual Meeting of the Northwest Section of the APS
Volume 55, Number 6
Friday–Saturday, October 1–2, 2010; Walla Walla, Washington
Session H3: Condensed Matter II |
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Chair: Karen Kavanagh, Simon Fraser University Room: Brattain Auditorium, Science 100 |
Saturday, October 2, 2010 1:30PM - 2:06PM |
H3.00001: Interference of electron diffracted beams from crystals and amorphous materials to measure their structure, mean inner potential and coherence properties Invited Speaker: This talk presents electron interferograms of crystals and amorphous materials used to measure their structure, mean inner potential and the coherence properties of their quasiparticles such as phonons, plasmons and, hopefully in the future, magnons. Recent methods of k-space interference has revealed that practically all electron intensities on the diffraction plane of a modern TEM have sufficient coherence to produce interferograms when self-interfered under a wide range of diffraction conditions. These diffraction intensities are of interest because they represent the material's atomic structure, which for amorphous materials has not yet been solved because of their complexity and missing phase information. For amorphous materials, two new methods of electron interference have been creaated. One is a wavefront-splitting method used for a-C, a-Si, a-Ge, SiO$_{2}$, a-W and a-ZrNiFe metal. The other is an amplitude spitting method that interferes a crystal's Bragg diffracted beams that contains intensities of an amorphous thin film on the crystal's surface. The fringes in these interferograms have been produced to high scattering angles necessary to remove dynamic diffraction effects in order to measure the coherence of the quasiparticles. Although relative phase information of materials has been obtained, the absolute phase may be obtainable using a new electron holography microscope having multiple electron biprisms, an imaging energy filter and an excellent coherent source soon to be received by UVic and open for use by everyone. An immediate application of the wavefront-splitting method is as a new method to measure the spatial resolution of the TEM, which occurs at the shear angle for fringe disappearance that is easily controlled using the electron biprism and measured by a Fourier transform showing realization from previous possibilities. [Preview Abstract] |
Saturday, October 2, 2010 2:06PM - 2:18PM |
H3.00002: Ga Site Determination in GaxFe3-xO4 Nanoparticles Vanessa Pool, Michael Klem, C. Chorney, Elke Arenholz, Yves Idzerda In this study, magnetic GaxFe3-xO4 nanoparticles with gallium doping (x=.15 to 1) were measured using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) to ascertain the Ga dopant site in the spinel structure and the affect of the Ga on the overall electronic structure of the nanoparticle. Ga has been doped into Fe3O4 nanoparticles by mixing Fe(acac)3, 1,2-hexadecanediol, benzyl ether, oleic acid, and oleylamine under evacuated conditions. A Neel-Arrhenius plot of the frequency-dependent alternating-current Magnetic Susceptibility (ACMS) measurements showed these particles to be weakly interacting with a reduction of the cubic anisotropy energy term with Ga concentration. The XAS and XMCD spectra were compared to powder standards and molecular-orbital calculations to determine that the Ga dopant is substituting into the tetrahedral A-site of the spinel structure, resulting in an overall increase (up to 50 percent) in the total moment of the material. Interestingly, the element specific XMCD spectra show that the average Fe moment is observed to increase with Ga concentration, a result consistent with the replacement of A-site Fe by Ga. [Preview Abstract] |
Saturday, October 2, 2010 2:18PM - 2:30PM |
H3.00003: Solubility of indium probe atoms in supercooled gallium liquid metal between 8K and 300K Xiangyu Yin, Randal Newhouse, John Bevington, Gary Collins Liquid gallium samples were made that remain supercooled down to 8 K. Perturbed angular correlation (PAC) measurements were made over the range 8-293 K to determine nuclear quadrupole interactions at 111In/Cd probe atoms doped into the gallium at the part-per-billion level. Near 295 K, the PAC spectrum exhibits a signal with a constant anisotropy (signal 1) for nearly all Cd probes that is consistent with extreme motional averaging of electric field gradients. This is typical of probe atoms dissolved in liquids. Cooling below 295 K, signal 1 is progressively replaced by a high-frequency, broadly-distributed quadrupole interaction signal (signal 2) that is attributed to probe atoms adhering to bounding walls of the gallium drop. The changes are reversible and attributed to changes in the terminal solubility of solutes in gallium with temperature. The observed fractions of indium in solution were approximately 100{\%} at 295 K, 50{\%} at 283 K, 15{\%} at 140 K and 10{\%} at 73 K. [Preview Abstract] |
Saturday, October 2, 2010 2:30PM - 2:42PM |
H3.00004: Electrodeposition of Metal on GaAs Nanowires Chao Liu, Omid Einabad, Simon Watkins, Karen Kavanagh Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60$^{\circ}$C. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field. [Preview Abstract] |
Saturday, October 2, 2010 2:42PM - 2:54PM |
H3.00005: Magnetic Anisotropy of single crystal Fe$_{1-x}$Ga$_{x}$ films deposited on ZnSe(110) H. Li, A. McClure, I. Vrable, G. Malovichko, Y.U. Idzerda Magnetoelastic alloys in the thin film form that are pinned to a substrate are of current interest as materials for controlled spin dynamic damping. Because of the strain generated in the thin film plus the anisotropic strain relaxation, the magnetic anisotropy properties change. In this research, single crystal Fe$_{1-x}$Ga$_{x }$films were grown on ZnSe(110) using MBE and characterized using ferromagnetic resonance. As the Ga concentration increases, the uniaxial and cubic anisotropy terms changed signed. Cubic anisotropy showed similar value as bulk material while uniaxial anisotropy is much larger than that for films grown on (100) surfaces. The increased term is attributed to the larger anisotropic lattice relaxation in Fe$_{1-x}$Ga$_{x}$/ZnSe(110) films. [Preview Abstract] |
Saturday, October 2, 2010 2:54PM - 3:06PM |
H3.00006: Magnetic stability of FeO/Fe3N nanoparticles under ion irradiation Jennifer Anand Sundararajan, Dongtao Zhang, You Qiang, Weilin Jiang Ion irradiation effects on the magnetic properties of FeO/Fe3N (Iron oxide/Iron Nitride) nanoparticles are investigated in this study. The FeO/Fe3N nanoparticles were prepared using a nanocluster deposition system in which pure iron nanoparticles were generated and allowed to react with oxygen and nitrogen gases and subsequently deposited onto a silicon wafer substrate. The XRD data confirms the presence of FeO and Fe3N compounds in the particles. The saturation magnetization of these nanoparticles measured by VSM was found to be around 37.54 emu/g. The coercivity (87.9 Oe) and remanence (3.2 emu/g) of these particles remains unaltered after irradiation with 5.5 MeV Si2+ ions to a fluence of 1016 ions/cm2 at room temperature, indicating that the magnetic properties of those nanoparticles are not affected even in a highly radioactive environment. The magnetic stability can provide us promising applications for advanced data storage. [Preview Abstract] |
Saturday, October 2, 2010 3:06PM - 3:20PM |
H3.00007: BREAK
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Saturday, October 2, 2010 3:20PM - 3:56PM |
H3.00008: Physical Adsorption on an Individual Carbon Nanotube Invited Speaker: I will present results from physical adsorption experiments on individual carbon nanotubes. A suspended closed-end single-wall nanotube driven at its resonance frequency, $f_{res}$, can be used as a pristine substrate and an ultrasensitive mass balance. Adsorption changes the suspended mass and $f_{res} \propto[M_{nt}+M_{ads}]^{-1/2}$, where $M_{nt}$ and $M_{ads}$ are respectively the masses of the bare nanotube and the adsorbates. For each yocto-balance (10$^{-24}$kg sensitivity) the nanotube, suspended across a $\mu$m-wide trench on a substrate with evaporated Pt conducting pads, is grown by CVD as the last step in the fabrication. The current through, and charge and tension on the nanotube are controlled via three electrodes (source, drain and gate). The nanotube is driven to vibrate using a modulated (1 kHz) AC current in the 1 MHz to 1 GHz range. Usually several resonances are detected and tracked as a function of gate voltage. To measure an isotherm, a chosen resonance is followed at constant temperature as a function of pressure of gas in equilibrium with the adsorbate. Simultaneous conductance measurements can be performed. With these devices we have studied the adsorption of Ar above 46K, Kr above 68 K, and $^4$He between 4K and 6K. We observe two-dimensional vapor (V), fluid, commensurate solid (CS) and incommensurate solid phases, and the transitions between them. We observe a change in the conductivity of the nanotube at a V-CS transition. I will compare briefly the adsorption on individual nanotubes with adsorption on nanotube bundles and exfoliated graphite. This work is carried out currently in collaboration with D. Cobden, Z. Wang, H.-C Lee, E. Frederickson and R. Roy. [Preview Abstract] |
Saturday, October 2, 2010 3:56PM - 4:08PM |
H3.00009: Development of a high-sensitivity torsion balance to study the Casimir/van der Waals interactions Woo-Joong Kim In this talk, we report on the development of a torsion balance currently underway at Seattle University. The completed torsion balance will enable us to explore the Casimir/van der Waals interactions between graphene sheets in a sphere-plane geometry. Particular experimental emphasis will be given on surface electric effects arising from real materials. As recently pointed in the literature, some of the previous Casimir force experiments conducted between a pair of metallic plates could have suffered from additional electric background forces. We will propose possible strategies to account for some of these background forces by employing Kelvin Probe Microscopy (KPM), thereby successfully extracting the fluctuation-induced interaction between layers of graphene. [Preview Abstract] |
Saturday, October 2, 2010 4:08PM - 4:20PM |
H3.00010: Composition dependences of jump frequencies in pseudo-binary phases Gary S. Collins, Randal Newhouse Jump frequencies of $^{111}$In/Cd probe atoms were earlier determined in PAC measurements on binary In$_{3}$La, In$_{3}$Pr, Sn$_{3}$La and other phases having the L1$_{2}$ structure [1]. In the present work, jump frequencies were measured for two kinds of pseudo-binary phases, the first having a mix of lanthanide elements, In$_{3}$(La$_{1-x}$Pr$_{x})$, and the second a mix of sp-elements, (In$_{1-x}$Sn$_{x})_{3}$La. Measurements exhibit modest inhomogeneous broadening that was greatest for $x \quad \sim $0.5, indicating that mixed elements were located more or less at random on their sublattice. The jumps detected are of probe atoms on the In or (In,Sn) sublattice. For both kinds of pseudo-binary phases, it was found that the jump frequency decreased rapidly with increasing x. However, the observed decrease was much more rapid for (In,Sn) mixing than for (La,Pr) mixing. Thus, it is found that the presence of solutes on the diffusion sublattice itself has a more profound effect on the jump frequency. Further systematics will be presented and discussed. \textit{Supported in part by the NSF under grant DMR 09-04096 (Metals Program).}\\[4pt][1] G.S. Collins et al., Phys. Rev. Lett. 102, 155901 (2009), and refs. therein. [Preview Abstract] |
Saturday, October 2, 2010 4:20PM - 4:32PM |
H3.00011: Shock compression of natural and synthetic diamond crystals along [100]: strength and elastic deformation J.M. Lang, Y.M. Gupta The strength and elastic response of natural and synthetic diamond was examined under shock compression. Diamond single crystals were shock compressed along the [100] orientation to peak elastic stresses between 60 and 120 GPa. Particle velocity histories and elastic shock wave velocities were measured using laser interferometry. A single elastic wave was observed in samples shocked up to $\sim $75 GPa and a two-wave elastic-inelastic response was observed in samples shocked to higher peak stresses. The elastic wave amplitudes for both sample types were comparable, however the time-dependent inelastic response showed significant differences between the sample types. Surprisingly, the elastic limits were lower for the higher peak stress. The elastic response of both samples types lie along the same stress-strain curve, from which the third-order elastic constant $C_{111}$ was determined. This is the first measurement of a third-order elastic constant of diamond determined solely from experimental results. [Preview Abstract] |
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