Bulletin of the American Physical Society
2016 Annual Meeting of the APS Mid-Atlantic Section
Volume 61, Number 16
Saturday–Sunday, October 15–16, 2016; Newark, Delaware
Session C1: Chemical Physics |
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Chair: Matt DeCamp, University of Delaware Room: Sharp Laboratory 123 |
Saturday, October 15, 2016 2:00PM - 2:36PM |
C1.00001: Energy Dependence of Ultrafast Electron Transfer at Interfaces. Invited Speaker: Lars Gundlach Electron transfer at semiconductor interfaces is a critical process in surface catalysis, novel electronic applications and solar energy conversion. The fast kinetics (sub-100 fs) and the often inhomogeneous environment complicate identifying the parameters that dominate the reaction. We present ultrafast spectroscopic studies of electron transfer between molecular electron donors and metal oxide semiconductors with well-defined variations in excess energy and dipole moment. Three Zn(II) tetraphenylporphyrins (ZnTPP) with alternating dipole moment attached to TiO$_{\mathrm{2}}$ colloidal films have been investigated. Surprisingly, electron injection dynamics does not show the expected dipole dependence. These results are substantiated by measurements employing a different molecular electron donor with two distinct excited states. Electron transfer times for both states were very similar and around 50 fs despite a 1 eV difference in excess energy. These results indicate that electron transfer at colloidal interfaces involves only a subset of the surface projected density of state (DOS) that is present in the metal oxide conduction band. This complicates predictions of electron transfer efficiency based on steady state DOS calculations. [Preview Abstract] |
Saturday, October 15, 2016 2:36PM - 2:48PM |
C1.00002: Theoretical Studies on the Effect of Strong Magnetic Fields on Water Hemanadhan Myneni, Dariusz Kedziera, Krzysztof Szalewicz, Jan W. Andzelm, Erik I. Tellgren, Trygve Helgaker Magnetic effects on water still remains a highly controversial topic due to low reproducibility and little consistence of the reported experiment results. Uncontrollable factors such as magnetic impurities, quantity of dissolved oxygen etc might be the possible source for these discrepancy. A theoretical investigation is performed by studying the effects of strong magnetic-field on a simple water cluster, (H$_2$O)$_2$, and on an aqueous solution to outline the role played by the dissolved oxygen. For the later, we considered a simple oxygen-water mixture with 1:2 ratio, (H$_2$O)$_2 \cdot $ O$_2$, and is much larger than 1:200,000 present in natural liquid water. The effect of oxygen molecules are unlikely to explain the results of the experiments reporting changes of liquid water properties in strong magnetic fields. [Preview Abstract] |
Saturday, October 15, 2016 2:48PM - 3:00PM |
C1.00003: Adsorption of Gases on Graphene Hawazin Alghamdi, Silvina Gatica We simulate the adsorption of H2O, NO2, and N2 on graphene using the method of Molecular Dynamics. The simulations are done at constant temperature that ranged from 100K to 250K. The H2O and NO2 molecules are modeled as a rigid 3-point system with Lennard-Jones and Coulomb's interactions. The motivation of the work is to test the capability of graphene to separate water or Nitrogen Dioxide from the air. We have found that a film forms on graphene at the lowest temperatures. . [Preview Abstract] |
Saturday, October 15, 2016 3:00PM - 3:12PM |
C1.00004: Nanoscale manipulations of the structural and electronic phases in VO$_{\mathrm{2\thinspace }}$. Mina Aziziha, Dustin Schrecongost, Weitao Dai, Haitian Zhang, Roman Engel-Herbert, Cheng Cen Vanadium Dioxide is a strongly correlated transition metal oxide with a metal-insulator transition at 340 K. Here we studied the phase transitions locally induced in VO$_{\mathrm{2}}$ by biased conducting AFM probe. Firstly, a monoclinic to rutile-like structural transition can be produced by positive probe biases in air. This effect is attributed to the field ionization of surface adsorbed water and the subsequent ion injection into the VO$_{\mathrm{2}}$ film. Secondly, a very stable layered structure can be generated from the rutile-like phase. The nature of the new phase, likely VO$_{\mathrm{2}}$. H$_{\mathrm{2}}$O, is still under active investigations. Near field scanning optical microscopy, Raman spectroscopy and electrical measurements were performed to image the phase transitions in nanoscale and characterize the related physical properties changes. [Preview Abstract] |
Saturday, October 15, 2016 3:12PM - 3:24PM |
C1.00005: Electron transfer from single quantum dot to individual acceptor molecules Haixu Leng, James Loy, Victor Amin, Emily Weiss, Matthew Pelton The charge transfer rate from a single quantum dot to viologen molecules is studied by time-resolved photoluminescence measurements at the single-nanocrystal level. These hybrid structures are model systems for the understanding of the potential to serve as the basis of next-generation photovoltaic and photocatalytic devices. Previous ensemble measurements on quantum-dot / molecule complexes have been unable to directly resolve the charge-transfer rate from a quantum dot to a single molecule, because of the random distribution of the number of adsorbed molecules on each dot. By making measurements at the single-particle level, we are able to push the sensitivity of charge-transfer measurements down to the level of single acceptor molecules. For each QD measured, the electron-transfer rate is constant over time, and the photoluminescence blinking dynamics are independent of the measured transfer rate. The total electron-transfer rate is distributed in discrete, constant increments, corresponding to discrete numbers of adsorbed molecules on each QD. The measurement provides an optical method to count the number of active acceptor molecules bound to a single nanocrystal. [Preview Abstract] |
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