Bulletin of the American Physical Society
80th Annual Meeting of the APS Southeastern Section
Volume 58, Number 17
Wednesday–Saturday, November 20–23, 2013; Bowling Green, Kentucky
Session BB: Condensed Matter and Nanoscience I |
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Chair: Richard Haglund, Vanderbilt University Room: 1 |
Thursday, November 21, 2013 8:30AM - 9:06AM |
BB.00001: Initial to multilayer growth transition of diF-TES-ADT Invited Speaker: Brad Conrad The importance of the non-covalent Fluorine-Sulfur and Fluorine-Fluorine interactions in driving 2D molecule self-assembly will be discussed in terms of organic semiconductor design. Observed structures and crystal growth of 2,8-difluoro-5,11-triethylsilylethynyl anthradithiophene (diF-TES-ADT) are put in context of bulk measurements and device performance measurements. Scanning Tunneling Microscopy studies of the growth of diF-TES-ADT on Au(111) from the submonolayer to several molecular layer regime were undertaken to elucidate the macroscopic growth of diF-TES-ADT on Au contacts. Two crystal structures are observed, both displaying diF TESADT backbone planes parallel to the substrate. Submolecular resolution imaging of the first monolayer ordered film regions realizes structures with close approach of Fluorine-Sulfur and Fluorine-Fluorine atoms of alternating molecules. Scanning Tunneling Spectroscopy measurements indicate a transport gap of 2.4 eV which is insensitive to local domain. After a disordered second layer growth, the third molecular layer displays excellent crystallinity with multiple domains. The fourth molecular layer mimics the third, indicating a transition to bulk crystal formation. These measurements are related to very recent device data and put in context of other growth studies. [Preview Abstract] |
Thursday, November 21, 2013 9:06AM - 9:42AM |
BB.00002: Plasmonic Interactions between Gold Nanoantennas and Vanadium Dioxide at Near Infrared Energies Invited Speaker: Davon Ferrara Nanocomposites made of noble metals and phase-changing materials are an interesting class of switchable metamaterials, as the localized surface plasmon resonance (LSPR) frequency of the nanocomposite can be modulated by the phase transition. Of this class of nanocomposites, gold nanoparticle (NP) arrays embedded in a vanadium dioxide (VO$_{2}$) film has several unique advantages, including the ability to induce the semiconductor-to-metal (SMT) phase transition of the VO$_{2}$ at a critical temperature of only 68$^{\circ}$C. For lithographically produced arrays of NPs between 140~nm and 180~nm, the LSPR has significant overlap with the 1.4~eV electronic transitions of the VO$_{2}$ 3d band. These electrons become strongly-correlated during the phase transition and delocalize to form the metallic conduction band at higher temperatures. Here we use an array of 180-nm diameter Au NPs embedded in a 60-nm VO$_{2}$ film as a nanoscale probe of the SMT in the VO$_{2}$. Temperature-dependent extinction measurements were carried out on the nanocomposite array using the plain VO$_{2}$ film as a reference to observe the hysteresis of the LSPR energy and linewidth. The interaction resulted in a 30\% reduction in plasmon dephasing time as the effective dielectric function of the VO$_{2}$ transitions from Lorentzian resonance to a Drude metal near 1.4~eV. Also, an array of 140-nm diameter Au NPs were used toincrease the efficiency of low-intensity laser switching in the nanocomposite compared to a plain 60-nm thick VO$_{2}$ film. An analytical model of laser heating was developed and suggests that the nanocomposite can be optimized to tune both optical and photothermal switching properties of an active metamaterial. [Preview Abstract] |
Thursday, November 21, 2013 9:42AM - 10:18AM |
BB.00003: The Role of Morphology in Promoting Self-healing in Cobalt Nanomaterials Invited Speaker: Jason Hattrick-Simpers Oxidative corrosion is a ubiquitous degradation mechanism that cuts across the entire landscape of materials science, surface science, chemistry, and surface physics. In the case of transition metal nanomaterials, oxidation often proceeds rapidly to completion, and obscures the unique properties associated with the metals. Here we use operando Raman and X-ray absorption fluorescence spectroscopic studies to demonstrate that cobalt nanorods exposed to oxidative conditions exhibit substantially different oxidation properties compared to their nanosphere analogs. In particular, in the case of the nanorods an oscillatory oxidation/reduction behavior is observed that preserves the metal surface of the nanomaterial indefinitely. This behavior is confirmed by Fischer-Tropsch (FT) catalysis studies, which clearly demonstrate that as opposed to the nanospheres, which oxidize rapidly in the presence of moisture, FT reactions on cobalt nanorods are unperturbed by water in the feed. High-resolution transmission electron microscopy studies reveal that the differences in oxidation behavior observed stem from the crystallographic faceting of the respective nanomaterials. In particular, the \textbraceleft 110\textbraceright planes exposed by the cobalt nanorods present the readily reducible Co$^{\mathrm{3+}}$ ions at the surface of the nanomaterial, effectively promoting reduction of the oxide during its growth. [Preview Abstract] |
Thursday, November 21, 2013 10:18AM - 10:54AM |
BB.00004: Understanding electronic and mechanical properties of graphene down to atomic scale Invited Speaker: Masahiro Ishigami Nanoscale materials are sensitively influenced by atomic scale defects and adsorbates. Such sensitivities can be used to impart various functionalities to develop new device technologies, but they can also introduce a large uncontrollable variability to measurements and mask the intrinsic properties. Using a unique approach to control experiments down to atomic scale, my laboratory performs quantitative measurements on nanoscale materials. In this talk, I will discuss two example scientific problems to demonstrate the capability of our experimental approach. The first problem is on the origin of the variability of field effect mobility of graphene on silicon oxide. This highly debated problem has a large impact on the utility of graphene in electronics. There are two main ``suspects'' (charged impurities and atomic scale defects) with different carrier scattering strengths. In the absence of any knowledge of the number of scatterers as a function of mobility, arguments on this topic have been rendered non-scientific. Over the last three years, we have developed a new quantitative method to count the number of scatterers in graphene with known carrier mobility and are able to determine that charged impurities are the culprit for the observed variability. The second problem is on the temperature-dependent friction of gold nanoparticles on graphene. This problem is important for nanoscale electromechanical systems (NEMS). By controlling the atomic scale environment between the nanoparticles and graphene, we have determined the friction as a function of temperature. Our result represents the first quantitative measurement of the frictional forces on nanoparticles and paves way for understanding temperature-dependent friction at nanoscale. [Preview Abstract] |
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