Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R26: Chemical Physics at the Nanoscale |
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Sponsoring Units: DCP Chair: Wilson Ho, University of California, Irvine Room: 289 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R26.00001: An ab-initio study on the stability of ZnO(0001)-Zn surfaces in an electrochemical environment Su-Hyun Yoo, Mira Todorova, Joerg Neugebauer Zinc oxide, a wide bandgap semiconductor, is widely studied due to its various applications in different fields such as (photo-)catalysis, protective coatings, optoelectronics and others. Understanding the impact an aqueous environment has on the ZnO properties is important for several of these. Focusing on the polar Zn terminated ZnO(0001) surface we combine density functional theory (DFT) calculations with thermodynamic concepts to study the stability of surface structures in contact with different environments. Extending our previous studies on the stability of ZnO(0001) surface phases in dry and humid environment [1], we utilize our recent developments [2] to construct surface Pourbaix diagrams, which describe surface stability in dependence of the pH and electrode potential conditions of the aqueous environment. We find that the presence of the solvent has a large qualitative effect on the phase diagram stabilising triangular structures over adatom/vacancy-type structures. [1] M. Valtiner, M. Todorova, G. Grundmeier, and J. Neugebauer, Phys. Rev. Lett. 103, 065502 (2009) [2] M. Todorova and J. Neugebauer, Phys. Rev. Applied 1, 014001 (2014) [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R26.00002: Importance of many-body dispersion and temperature effects on gas-phase gold cluster (meta)stability Bryan R. Goldsmith, Philipp Gruene, Jonathan T. Lyon, David M. Rayner, Andr\'{e} Fielicke, Matthias Scheffler, Luca M. Ghiringhelli Gold clusters in the gas phase exhibit many structural isomers that are shown to intercovert frequently, even at room temperature. We performed ab initio replica-exchange molecular dynamics (REMD) calculations on gold clusters (of sizes 5-14 atoms) to identify metastable states and their relative populations at finite temperature, as well as to examine the importance of temperature and van der Waals (vdW) on their isomer energetic ordering. Free energies of the gold cluster isomers are optimally estimated using the Multistate Bennett Acceptance Ratio. The distribution of bond coordination numbers and radius of gyration are used to address the challenge of discriminating isomers along their dynamical trajectories. Dispersion effects are important for stabilizing three-dimensional structures relative to planar structures and brings isomer energetic predictions to closer quantitative agreement compared with RPA@PBE calculations. We find that higher temperatures typically stabilize metastable three-dimensional structures relative to planar/quasiplanar structures. Computed IR spectra of low free energy Au$_9$, Au$_{10}$, and Au$_{12}$ isomers are in agreement with experimental spectra obtained by far-IR multiple photon dissociation in a molecular beam at 100 K. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R26.00003: Site-specific polarizabilities as descriptors of metallic behavior in atomic clusters Koblar Jackson, Julius Jellinek The electric dipole polarizability of a cluster is a measure of its response to an applied electric field. The site specific polarizability method decomposes the total cluster polarizability into contributions from individual atoms and also allows it to be partitioned into charge transfer and electric dipole contributions. By systematically examining the trends in these quantities for several types of metal atom clusters over a wide range of cluster sizes, we find common characteristics that uniquely link the behavior of the clusters to that of the corresponding bulk metals for clusters as small as 10 atoms. We discuss these trends and compare and contrast them with results for non-metal clusters. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R26.00004: Critical Length and Heat of Fusion of Organic Compounds inside Nano Pores. Samuel Amanuel, Jason Turner, Alexander Clain, Caleb Novins We probed the first order phase transition of physically confined organic compounds inside nano pores using a Differential Scanning Calorimeter (DSC). Both melting and freezing temperatures of the physically confined systems decreased with the physical size of the materials and scaled linearly with the inverse of their size. While these are in agreement with the Gibbs-Thomson equation, contrary to the assumptions used in developing the equation, the apparent heat of fusion did not remain invariant with size. The apparent heat of fusion decreased as the physical size of the materials decreased. And there appears to be a critical length below which the decrease in the apparent heat of fusion is more pronounced. We have attempted to distinguish between the apparent (measured) and "true" heat of fusion and have demonstrated how the apparent heat of fusion can be altered through thermal history. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R26.00005: Symmetry and Magnetism in Ni$_{\mathrm{9}}$Te$_{\mathrm{6\thinspace }}$clusters ligated by CO or Phosphine Ligands. Vikas Chauhan, Arthur Reber, Shiv Khanna The removal of a single ligand from the magnetic Ni$_{\mathrm{9}}$Te$_{\mathrm{6}}$(L)$_{\mathrm{8}}$ (L$=$P(CH$_{\mathrm{3}})_{\mathrm{3}}$, CO) clusters is found to quench the magnetic moment. The reduction in magnetic moment is caused by a geometric deformation of the Ni$_{\mathrm{9}}$Te$_{\mathrm{6}}$ core that breaks the octahedral symmetry of the cluster. This effect is observed in both the CO and phosphine based ligands. The octahedral symmetry bare cluster is also found to have a large magnetic moment. These results highlight the dilemma faced by magnetic ligand protected clusters whose symmetry has been broken: whether to break the spin symmetry as in Hund's rules, or to break the spatial symmetry as in the Jahn-Teller effect. The spatial symmetry breaking is found to be an oblate distortion that forms additional Ni-Te bonds resulting in the enhanced stability of the cluster. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R26.00006: Hexagonal bubble formation and nucleation in sodium chloride solution Lifen Wang, Lei Liu, Ali Mohsin, Jianguo Wen, Gong Gu, Dean Miller The bubble is formed frequently at a solid-liquid interface when the surface of the solid or liquid has a tendency of accumulating molecular species due to unbalanced surface hydrophobicity attraction\footnote{~Emily E. Meyer \textit{et al}. \textit{PNAS} \textbf{103}, 15739 (2006)}\footnote{~Detlef Lohse \textit{et al}. \textit{Rev. Mod. Phys.} \textbf{87}, 0034 (2015)}. Morphology and shape of the bubble are thought to be associated with the Laplace pressure that spherical-cap-shaped object are commonly observed\footnote{~Dongha Shin \textit{et al}. \textit{Nat. Commun.} \textbf{6}, 6068 (2015)}. Dynamic surface nanobubble formation and nucleation in the controlled system have been not fully investigated due to the direct visualization challenge in liquid systems. Here, utilizing in situ TEM, dynamic formation and collapse of spherical-shaped nanobubbles were observed at the water-graphene interface, while hexagonal nanobubbles grew and merged with each other at water-crystalline sodium chloride interface. Our finding demonstrates that different hydrophobic-hydrophilic interaction systems give rise to the varied morphology of surface nanobubble, leading to the fundamental understanding of the interface-interaction-governed law on the formation of surface nanobubble. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R26.00007: Nanorod Mobility within Entangled Wormlike Micelle Solutions Jonghun Lee, Aline Grein-Iankovski, Suresh Narayanan, Robert Leheny In the semi-dilute regime, wormlike micelles form an isotropic entangled microstructure that is similar to that of an entangled polymer solution with a nanometer-scale entanglement mesh size. We report a combined x-ray photon correlation spectroscopy and rheology study to investigate the translational dynamics of gold nanorods in entangled wormlike micelles formed by the surfactant cetylpyridinium chloride (CPyCl) and the counterion sodium salicylate (NaSal). The CPyCl concentration is varied to tune the entanglement mesh size over a range that spans from the nanorod diameter to the nanorod length. On short time scales the nanorods are localized on a length scale of the entanglement mesh as long as the mesh size is smaller than the nanorod length. On longer time scales, the nanorods undergo free diffusion. At the highest CPyCl concentrations, the nanorod diffusivity approaches the value expected based on the macroscopic viscosity of the solutions, but it increases with decreasing CPyCl concentration more rapidly than expected from the macroscopic viscosity. A recent model for nanoparticle ``hopping'' diffusion in entangled polymer solutions accounts quantitatively for this enhanced diffusivity [Macromolecules 2015, 48, 847]. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 9:36AM |
R26.00008: Applications of Fermi-Lowdin-Orbital Self-Interaction Correction Scheme to Organic Systems Tunna Baruah, Der-You Kao, Yoh Yamamoto Recent progress in treating the self-interaction errors by means of local, Lowdin-orthogonalized Fermi Orbitals offers a promising route to study the effect of self-interaction errors in the electronic structure of molecules. The Fermi orbitals depend on the location of the electronic positions, called as Fermi orbital descriptors. One advantage of using the Fermi orbitals is that the corrected Hamiltonian is unitarily invariant. Minimization of the corrected energies leads to an optimized set of centroid positions. Here we discuss the applications of this method to various systems from constituent atoms to several medium size molecules such as Mg-porphyrin, C$_{60}$, pentacene etc. The applications to the ionic systems will also be discussed. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R26.00009: Organic radical formation over transition metal oxides: Bonding trends studied with inelastic neutron scattering Matthew Patterson, Richard Kurtz, Randall Hall, Erwin Poliakoff, Phillip Sprunger Environmentally persistent free radicals (EPFRs), a class of long-lived pollutants (lifetimes of 1-1000 hours) consisting of aromatic molecules chemisorbed to metal oxide-containing particulate matter, have significant public health impacts, having been demonstrated to produce pulmonary and cardiovascular dysfunction in animal models. Oxides of many environmentally abundant first-row transition metals form EPFRs, so a fundamental understanding of their formation mechanisms is crucial in developing strategies for their prevention and remediation. On most metal oxides, EPFRs form through electron transfer from an adsorbed organic such as phenol to a metal cation, reducing the cation; however, we demonstrate here that the opposite process uniquely occurs in ZnO, in which electrons are transferred from Zn to the adsorbed phenoxy group, creating the longest-lived known EPFR species. Using inelastic neutron scattering, we have probed vibrational excitations in model EPFR systems -- chemisorbed phenol on ZnO, CuO, Fe$_{2}$O$_{3}$, and TiO$_{2}$ nanoparticles -- in order to correlate their vibronic structure with known trends in their electronic structure and lifetimes. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R26.00010: Nonequilibrium diagrammatic technique for Hubbard Green functions Feng Chen, Maicol Ochoa, Michael Galperin Utilizing many-body states of the isolated molecule, Hubbard nonequilibrium Green function (NEGF) is able to account for the intra-system interactions exactly while coupling to the contacts is treated perturbatively. We introduce nonequilibrium diagrammatic technique for the Hubbard NEGF, which allows building controlled approximations for both Green (two-time) and multi-time correlation functions. The formulation is an extension of equilibrium considerations for strongly correlated lattice models to nonequilibirum realm of current carrying molecular junctions. We demonstrate viability of the approach with numerical simulations for a generic junction model of quantum dot coupled to two electron reservoirs. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R26.00011: Multiscale Modeling of Plasmon-Exciton Dynamics of Malachite Green Monolayers on Gold Nanoparticles Holden Smith, Tony Karam, Louis Haber, Kenneth Lopata A multi-scale hybrid quantum/classical approach using classical electrodynamics and a collection of discrete two–level quantum system is used to investigate the coupling dynamics of malachite green monolayers adsorbed to the surface of a spherical gold nanoparticle (NP). This method utilizes finite difference time domain (FDTD) to describe the plasmonic response of the NP and a two-level quantum description for the molecule via the Maxwell/Liouville equation. The molecular parameters are parameterized using CASPT2 for the energies and transition dipole moments, with the dephasing lifetime fit to experiment. This approach is suited to simulating thousands of molecules on the surface of a plasmonic NP. There is good agreement with experimental extinction measurements, predicting the plasmon and molecule depletions. Additionally, this model captures the polariton peaks overlapped with a Fano-type resonance profile observed in the experimental extinction measurements. This technique shows promise for modeling plasmon/molecule interactions in chemical sensing and light harvesting in multi-chromophore systems. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R26.00012: Reversed Nanoscale Kirkendall Effect in Au$-$InAs Hybrid Nanoparticles Jing Liu, Anatoly Frenkel, Yorai Amit, Uri Banin Metal-semiconductor hybrid nanoparticles (NPs) have synergistic properties that have been exploited in photocatalysis, electrical, and optoelectronic applications. Rational design of hybrid NPs requires the knowledge of the underlying mechanisms of diffusion of the metal species through the nanoscale semiconductor lattice. The importance of understanding and controlling the co-diffusion of different constituents is demonstrated in the synthesis of various hollow-structured NPs via the Kirkendall effect. We used time-resolved X-ray absorption fine structure spectroscopy, X-ray diffraction and electron microscopy to monitor the diffusion process of Au atoms through InAs nanocrystals in real time. In this system the diffusion rate of the inward diffusing species (Au) is faster than that of the outward diffusion species (InAs), which results in the formation of a crystalline metallic Au core surrounded by an amorphous, oxidized InAs shell. These observations indicate that in hybrid Au-InAs NPs the rarely observed ``reversed nanoscale Kirkendall effect'' is in play. It presents a potentially new way to synthesize unique nanoscale core-shell structures. [Preview Abstract] |
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