Bulletin of the American Physical Society
2010 Annual Meeting of the California-Nevada Section of the APS
Volume 55, Number 12
Friday–Saturday, October 29–30, 2010; Pasadena, California
Session H1: Condensed Matter Physics and Materials Science III |
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Chair: Shirley Chiang, University of California, Davis Room: Building 74 - Beckman Institute Auditorium |
Saturday, October 30, 2010 1:00PM - 1:12PM |
H1.00001: Progress in the development of scanning ultrafast electron microscopy Ding-Shyue Yang, Omar Mohammed, Ahmed Zewail In recent years, ultrafast electron microscopy (UEM) has been developed as a technique that enables time-dependent imaging of structural dynamics in the condensed phase. The central concept involves the usage of a femtosecond or nanosecond laser pulse to initiate dynamical changes in the specimen, and a second light pulse that generates an electron packet as the probe for detection. In UEM, the electron pulses are accelerated typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy (SUEM) using a field-emission-source configuration, which is different from UEM's. Scanning of pulses is made with only one or a few electrons per pulse, thus achieving imaging still in ten(s) of seconds and without much of the space-charge effect between electrons. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in-situ 4D imaging and with environmental capability. [Preview Abstract] |
Saturday, October 30, 2010 1:12PM - 1:24PM |
H1.00002: On and Off Phonon Resonance Imaging of Silica Capped Gold Nanoparticles and Silica Nanoparticles by Infrared Near-Field Microscopy Brandon Hessler, Jerry Ochoa, Zach Nuno, Yohannes Abate Phonon resonant silicon dioxide (SiO2) nanoparticles and SiO2 coated gold nanoparticles were imaged using optical near-field microscopy in the infrared. Both the near-field amplitude and phases were obtained as a function of infrared wavelength. Locally excited silicon dioxide phonon polariton resonances occur around 9.26 micro meters. Experimental results are in good agreement with dielectric function model calculations for these particles in the extended dipole approximation. These results show that the phase signal intensity of the capped particles is stronger than the silica particles (by a factor of about 3) at resonance due to the effect of the highly reflective gold core. Since the near-field phase is proportional to the absorption cross-section of a particle, these results can be used to quantify the effect of a highly reflective surface on the absorptive properties of thin films. [Preview Abstract] |
Saturday, October 30, 2010 1:24PM - 1:36PM |
H1.00003: Photon-Induced Near Field Electron Microscopy: Theoretical and Experimental Sang Tae Park, Milo Lin, Ahmed Zewail 4D electron microscopy utilizes a pulsed electron packet to image structural dynamics of nanomaterial, induced by an optical pulse, in real time. In the presence of nanostructures, electrons can directly interact with photons, and either gain or lose light quanta. This near field photon-electron interaction enables visualization of nanoscale particles and interfaces with enhanced contrast, and is termed photon-induced near field electron microscopy (PINEM). Here, we give an account of the theoretical and experimental results of PINEM. In particular, the time-dependent Schr\"odinger equation for electron packets in the nanostructure-scattered electromagnetic (near) field is solved to obtain the evolution of the incident electron packet into discrete momentum wavelets. The characteristic length and time scales of the halo of electron- photon coupling are discussed in the framework of Rayleigh and Mie scatterings, providing the dependence of the PINEM effect on size, polarization, material, and spatiotemporal localization. [Preview Abstract] |
Saturday, October 30, 2010 1:36PM - 1:48PM |
H1.00004: Energy Transfer Networks in Highly Defective Materials Ted Laurence In highly defective materials, where the defect density approaches the atomic density, the electronic structure of the material may be expected to deviate strongly from descriptions provided by bulk solid state theory or molecular and atomic physics. For sufficient defect densities, significant interactions between defects may strongly affect the temporal and spectral characteristics of both excitation and emission of electronic excitations. Previously, we discovered a novel photoluminescence with a distribution of fast photoluminescence decay times in surface flaws in fused silica that is correlated with damage propensity with high fluence lasers. Here, we propose a model to explain the origin of this PL and provide evidence that this model is in effect in this system and in other highly defective systems. We propose that the distribution in lifetimes observed is not simply due to a large variety of defect states, but due to a variety of energy transfer interactions between defect states. These highly defective material properties are of especial significance at surfaces and in nanostructured materials. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Saturday, October 30, 2010 1:48PM - 2:00PM |
H1.00005: Study of Raft Domains in Model Membrane of DPPC/PE/Cholesterol Chai Lor, Linda Hirst Raft domains in bilayer membrane are thought to play an important role in many cell functions such as cell signaling or trans-membrane protein activation. Here we use a model membrane consisting of DPPC/PE/cholesterol to examine the structure of membrane rafts and phase interactions. In particular we are interested in lipids containing the highly polyunsaturated fatty acid DHA. We use both atomic force microscopy (AFM) and fluorescence microscopy to obtain information on the structural properties of raft regions and track cholesterol. As expected, we find phase separation of raft regions between saturated and unsaturated lipids. Moreover, we find that the roughness of the domains change with varying cholesterol concentration possibly due to overpacking. This model study provides further understanding of the role of cholesterol in bilayer membrane leading towards a better knowledge of cell membranes. [Preview Abstract] |
Saturday, October 30, 2010 2:00PM - 2:12PM |
H1.00006: Casein Kinase 2 Reverses Tail-Independent Inhibition of Kinesin-1 Jing Xu, Zhanyong Shu, Preetha Anand, Babu Reddy, Silvia Cermelli, Thomas Whisenant, Stephen King, Lee Bardwell, Lan Huang, Steven Gross Kinesin-1 is a plus-end microtubule-based molecular motor, and defects in kinesin transport are linked to diseases including neurodegeneration. Kinesin can auto-inhibit via a direct head-tail interaction, but is believed to be active otherwise. In contrast, this study uncovers a fast but reversible inhibition distinct from the canonical auto-inhibition pathway. The majority of the initially active kinesin (full-length or tail-less) loses its ability to bind/interact with microtubule, and Casein Kinase 2 (CK2) reverses this inactivation (up to 4-fold) without altering kinesin's single motor properties. Motor phosphorylation is not required for this CK2 -mediated kinesin activation. In cultured mammalian cells, knockdown of CK2 level, but not kinase activity, was sufficient to decrease the force required to stall lipid droplet transport, consistent with a reduction in the number of active motors. We propose that CK2 forms a positive regulating complex with the motor. This study provides the first direct evidence of a protein kinase positively regulating kinesin-transport, and uncovers a pathway whereby inactive cargo-bound kinesin can be activated. [Preview Abstract] |
Saturday, October 30, 2010 2:12PM - 2:24PM |
H1.00007: Multiscale modelling of Interaction of Alane Clusters on Al(111) surface: A Reactive Force Field and Infrared Absorption Spectroscopy Approach Julius Ojwang, Adri van Duin, William Goddard III, Rutger van Santen Alanes are believed to be the ubiquitous facilitators of mass transport of aluminum atoms during the thermal decomposition of NaAlH$_{4}$. Alanes also take part on decomposition of AlH$_{3}$, another important material for hydrogen storage. We have used interplay of theoretical simulations (reactive force field and density functional theory) and experiments (IR reflection absorption spectroscopy) to address the issue of the role of alanes as facilitators of mass transport of aluminum atoms. We have obtained valuable details on the mechanism of formation and agglomeration of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. The identification of these string like intermediates as a precursor to the bulk hydride phase allows us to explain the loss of resolution in surface IR experiments with increasing hydrogen coverage on single crystal Al(111) surface. This is in excellent agreement with the experimental works of Go et al. (E. Go, K. Thuermer, J.E. Reutt-Robey, Surf. Sci.,437:377(1999)). [Preview Abstract] |
Saturday, October 30, 2010 2:24PM - 2:36PM |
H1.00008: Phase separation instabilities in two-dimensional Betts clusters: exact results Armen N. Kocharian, Gayanath W. Fernando, Kun Fang The energy eigenvalues and eigenstates of the Hubbard model with nearest and next nearest neighbor hopping are calculated by exact diagonalization technique and Lanczos algorithm by exploiting the square symmetry of isotropic Betts square (cells) - clusters with periodic boundary conditions. The electron pairing instabilities, order parameters and quantum critical points (at one hole away from half filling) are evaluated by monitoring the charge and spin pairing gaps in a wide range of interaction strengths which show level crossings in the ground state and corresponding crossovers at finite temperatures. The calculated critical behavior of the energy gap in optimized 8-site square symmetry lattice structures display universal features consistent with the exact results obtained for elementary bipartite square geometry [A. N. Kocharian et al., Phys. Rev. B 78, 075431 (2008)]. The effects of the next nearest neighbor hopping and temperature on these electron instabilities are also considered. Behavior of electrons in contrasting bipartite and non-bipartite two- and three-dimensional topologies display a number of inhomogeneous, paired and non-paired nanoscale phases seen in high T$_c$ cuprates, manganites. [Preview Abstract] |
Saturday, October 30, 2010 2:36PM - 2:48PM |
H1.00009: Signature of Aslamazov-Larkin fluctuation Hall conductivity in Tantalum Nitride films above their superconducting transition temperature Nicholas Breznay, Mihir Tendulkar, Aharon Kapitulnik, Karen Michaeli, Alexander Finkelstein We have studied the Hall effect in superconducting Tantalum Nitride films. We find a large contribution to the Hall conductivity near the superconducting transition, which we can track to temperatures well above Tc and magnetic fields well above the upper critical field, Hc2(0). This contribution arises from Aslamazov-Larkin type superconducting fluctuations, and we find quantitative agreement between our data and theoretical analysis based on time dependent Ginzburg-Landau theory. [Preview Abstract] |
Saturday, October 30, 2010 2:48PM - 3:00PM |
H1.00010: Dirac Point Degenerate with Massive Bands at a Topological Quantum Critical Point Swapnonil Banerjee, Warren Pickett, Justin Smith, Victor Pardo In the band structure of the Skutterudite, as the Sb sublattice in the unit cell is moved slightly retaining the crystal symmetry, the small gap at the Fermi energy closes due to a band crossing at Gamma. At this critical point a pair of linear (``Dirac'') bands are degenerate with two conventional bands. Because of the crystal symmetry three out of the four bands are degenerate even when one is away from the critical point. Insulators in 3D, as well as in 2D, can be characterized by topological invariants. When inversion symmetry is present (as in the space group 204 of Skutterudite), the Z2 invariant can be obtained from the parities of the occupied states at the invariant momenta, which in the bcc structure consist of Gamma, three H points, and the four P points. Here only the Gamma point requires consideration, since reoccupation occurs only there. The singlet has odd parity at Gamma while for the triplet it is even. As the critical point is crossed, the product of the parities of the occupied bands at Gamma, and hence the Z2 invariant, changes sign due to the reversal of the singlet- triplet position; the signal of a trivial to topological transition. [Preview Abstract] |
Saturday, October 30, 2010 3:00PM - 3:12PM |
H1.00011: Magnetoelectric response of LiNiPO$_{4}$ from first-principles Eric Bousquet, Nicola Spaldin, Philippe Ghosez The lithium orthophosphates LiMPO$_{4}$ (M = Mn, Fe, Co, Ni) have attracted large interest because of their potential use in cathode electrode for Li-ion batteries as well as their large magnetoelectric response and more recently because of the presence of ferrotoroidic domains in LiCoPO$_{4}$. Here we will discuss the response to a static magnetic field of LiNiPO$_{4}$ by means of first-principles calculations. This will allow us to extract the magnetic susceptibility as well as the magnetoelectric coefficients and to analyze their microscopic origin by decomposing the electronic and the ionic contributions. This last decomposition highlight the importance of the electronic contribution to the magnetoelectric response. [Preview Abstract] |
Saturday, October 30, 2010 3:12PM - 3:24PM |
H1.00012: Synthesis and Analysis of Rare-Earth Nanoparticles Gd and Nd Jose Amaral, Dulce Romero, Carmin Liang, Pei-Chun Ho, Saeed Attar, Dennis Margosan Magnetic nanoparticles can have enchanced magnetization and increase the density in a finite region when compared to their bulk material. This makes them ideal for applications in various fields such as biological markers in medical MRI technology and magnetic refrigeration. At Fresno State we are synthesizing and characterizing rare-earth nanoparticles Gd and Nd by the inverse micelle method. Starting by using DDAB as a surfactant, GdCl$_3$ and NdCl were added to form inverse micelle solutions. A liquid-liquid extraction process was used to extract the magnetic clusters. The energy-dispersive X-ray (EDX) results show that Gd clusters less than 1 micrometer were produced. Images from the scanning electron microscope (SEM) and light microscope show spherical Gd clusters with excess DDAB and other by-products, indicating a successful reduction of GdCl$_3$. Future research will be geared towards substituting hexane for toluene and methanol for water to reduce oxygen amounts and to form Nd nanoparticles. [Preview Abstract] |
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