Bulletin of the American Physical Society
2011 Annual Meeting of the California-Nevada Section of the APS
Volume 56, Number 14
Friday–Saturday, November 11–12, 2011; Menlo Park, California
Session C2: Materials Sciences |
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Chair: Uwe Bergmann, SLAC National Accelerator Laboratory Room: Bldg 48 - ROB Redwood C/D |
Friday, November 11, 2011 4:00PM - 4:12PM |
C2.00001: Molecular Dynamics Modeling and Analysis of Actin Network Formation Ronald Pandolfi Actin filaments are ubiquitous and critical in cellular functions. The polymeric protein F-actin is a semi-flexible filament that forms networks in the presence of binding proteins (i.e. $\alpha$-actinin, Filamin, Fascin). Molecular dynamics modeling and simulation of the formation of these networks informs the dependence of network structure on the length and flexibility of these filaments. In comparative experimental work, filament length is controlled by the addition of Gelsolin. The calculation of radial pair distribution functions of simulated actin systems allows quantitative characterization of the network structure by bundling and mesh size. [Preview Abstract] |
Friday, November 11, 2011 4:12PM - 4:24PM |
C2.00002: Correlative Characterization of Li-S Batteries Using \emph{In situ} TXM and XRD Johanna Nelson, Sumohan Misra, Yuan Yang, Ariel Jackson, Yi Cui, Joy Andrews, Michael Toney Sulfur is an attractive Li-ion battery cathode material candidate because of its high specific energy (2600 Wh/kg); however, it is well known that Li-S batteries suffer from capacity loss or fading. It is generally accepted that this is due to the loss of active material and the formation of nonconducting Li$_2$S as a thin film coating the electrode. Both phenomena stem from the dissolution of active sulfur particles in the non-aqueous electrolyte as soluble long chain polysulfides form during the early stages of cell discharge. Using \emph{in situ}, high resolution transmission X-ray microscopy (TXM) at SSRL beam line 6-2 and \emph{in situ} X-ray diffraction (XRD) at beam line 11-3, we have explored initial discharge and charge cycle of Li-S batteries in real time. By combining these complementary methods, we can characterize the morphological changes of the active material as well as changes in crystallinity and crystal structure. We can then correlate these changes and the electrochemistry to better understand the reduction of elemental sulfur and various adaptations employed to retain battery capacity over many cycles. [Preview Abstract] |
Friday, November 11, 2011 4:24PM - 4:36PM |
C2.00003: Field Control of the Surface Electroclinic Effect in Liquid Crystal Displays Dana Hipolite, Maro Tsiifte, Karl Saunders Liquid crystals (LCs) are a fascinating class of materials exhibiting a range of phases intermediate between liquid and crystalline. Smectic LCs consist of elongated molecules arranged in a periodic stack (along z) of liquid like layers. In the smectic-A (Sm-A) phase, the average molecular long axis (director) points along z. In the smectic-C (Sm-C) phase, it is tilted relative to z, thus picking out a special direction within the layers. Typically, the Sm-A* to Sm-C* transition will occur as temperature is decreased. In chiral smectics (Sm-*A or Sm-C*) it is possible to induce director titling (i.e. the Sm-C* phase) from the Sm-A* phase via the application of an electric field. This is known as the ``bulk electroclinic effect'' (BECE). Often, e.g. in a LCD, the Sm-A* phase is in contact with a surface. The surface acts as a localized electric field, and induces a local tilt, i.e. a local Sm-C* phase. This ``surface electroclinic effect'' (SECE) leads to a distortion of the smectic layers, which reduces LCD quality. We present a model of the Sm-A*-Sm-C* transition, including both BECE and SECE. Analysis of this model shows that the SECE can be controlled, and even eliminated, by a bulk electric field. [Preview Abstract] |
Friday, November 11, 2011 4:36PM - 4:48PM |
C2.00004: 10nm spatial resolution in X-ray PEEM using diamondoid Hitoshi Ishiwata, Hendrik Ohldag, Andreas Sholl, Olav Hellwig, Z.X. Shen, Nick Melosh The spatial resolution in X-ray Photoemission Electron Microscopy typically does not allow imaging features smaller than 25nm. X-ray PEEM resolution is limited by chromatic aberrations caused by large energy spread of secondary electrons coming off of surface. Diamondoids have recently been shown to act as a monochromator for secondary electrons, thus reducing chromatic aberration in X-ray PEEM. In addition to improving the resolution of the microscope the diamondoid coating will also enhance the image intensity by reducing work function of surface. Without the diamondoid coating, X-ray PEEM reaches detection limit on contrast transfer at 25nm spatial resolution. However with diamondoid coating of surface, we have shown that spatial resolution could reach 10nm spatial resolution creating new record for X-ray PEEM spatial resolution. [Preview Abstract] |
Friday, November 11, 2011 4:48PM - 5:00PM |
C2.00005: Local Structure about Zn and Nb in LiNbO3:Zn Bradley Car Doped LiNbO$_3$ has a range of applications in optics, but how these effects emerge from the local structure particularly in doped materials, is poorly understood, as the substitution site(s) is still under debate. We present a detailed analysis of the local structure about Zn (7.3-11.1\%) in doped LiNbO$_3$ using the extended X-ray absorption fine structure (EXAFS) technique, in order to determine the defect substitution site. Our analysis shows that even for high Zn concentrations Zn substitutes on the Li site, but the environment about Zn is distorted. From Nb EXAFS the environment about Nb in the host crystal generally agrees very well with diffraction except for the first O shell which appears to have a third longer Nb-O distance - perhaps O on an interstitial site or OH$^{-}$. [Preview Abstract] |
Friday, November 11, 2011 5:00PM - 5:12PM |
C2.00006: Exploring Half Metals in Li-based Half Heusler Alloys B. Busemeyer, M. Shaughnessy, C. Y. Fong We examine the electronic and magnetic properties of three Li-related half Heusler alloys, namely LiMnN, LiMnP, and LiMnSi in a structure close to the well-known zinc-blende structure in the attempt to search for new half metallic materials. If they do demonstrate half metallic properties, this will open new grounds for finding half metallic spintronic materials. Our results will furnish guidelines for future exploration of alkali-related half metals. Using the primitive cell LiMnSi is a half metal, while the pnictides are not. However when the conventional cell is used, we find that Li$_3$Mn$_4$P$_4$ and Li$_3$Mn$_4$N$_4$ are half metals. The physical reason for these two pnictides to be half metallic and for their magnetic moment per unit cell will be presented. [Preview Abstract] |
Friday, November 11, 2011 5:12PM - 5:24PM |
C2.00007: Adsorption and desorption mechanisms for allylamine, propylamine, propylchloride, and propylene on the Si(100)-2x1 surface Lekh Adhikari, Sean Casey The mechanisms for adsorption and desorption of allylamine, propylamine, propylchloride, and propylene on the Si(100)-2x1 surface has been investigated experimentally using thermal desorption spectroscopy (TDS) and computationally using density functional theory (DFT) calculations. TDS was carried out to track down possible desorption products and their desorption temperatures and DFT calculations were done to help elucidate the experimental results, and to more fully probe mechanistic pathways consistent with the TDS results. All of these molecules are three carbon chain moieties with differing terminal functional groups and were chosen to self-consistently probe amine and alkene functional group chemistry on this surface. Results from the adsorption of propylene and allylamine were mostly consistent with previous studies on adsorption of these molecules, with the main difference being the observation of a prominent $m/z$ = 17 desorption product in the case of TDS after allylamine adsorption. TDS after propylamine and allylamine adsorption gave rise to a prominent propylene ($m/z$ = 42) desorption channel. The TDS results showed that propylene and halo-alkanes such as chloro-propane also display a propylene desorption channel, but it appears at a lower surface temperature than for the amines. This is an indication that the amine adsorption and decomposition mechanisms is different than halo-alkane or alkene reaction on the Si(100)-2x1 surface, in that it does not involve any silicon-carbon bond forming reactions initially. This is consistent with the computational results as well. [Preview Abstract] |
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