Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W43: Chemical Physics of Graphene and Other Crystals |
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Sponsoring Units: DCP Chair: Jeff Cina, University of Oregon Room: Hilton Baltimore Holiday Ballroom 2 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W43.00001: Mullite Ceramics at Extreme Conditions Patricia Kalita, Andrew Cornelius, Kris Lipinska, Oliver Hemmers, Stanislav Sinogeikin, Reinhard Fisher, Hartmut Schneider Mullite is perhaps one of the most important phases in both traditional and advanced ceramics and thus one of the most widely studied ceramic phases. Even though the thermo-elastic behavior of mullites have been studied extensively (spectroscopy, diffraction, dilatometry, theoretical simulations), there are only few studies into the effects of pressure on mullites. This work aims at filling this gap by examining the role of oxygen vacancies on the mechanical stability and on the bulk modulus of mullite-type structures. [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W43.00002: Chemical structure of multilayer oxidized epitaxial graphene Si Zhou, Angelo Bongiorno In this work, density functional theory (DFT) calculations are used to interpret new X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscope (AFM) measurements of the oxide of epitaxial graphene. This layered carbon material is obtained by Hummers oxidation of 6- to 17-layer graphene films grown epitaxially at high temperature on a silicon carbide substrate. The extensive DFT calculations carried out to solve the inverse problem posed by the aforementioned measurements show that a most plausible molecular structure for the oxide of epitaxial graphene consists of mildly oxidized graphene layers covalently bridged by short polyoxymethylene chains. Possible chemical reactions leading to this form of graphene derivative are discussed. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W43.00003: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W43.00004: Study on Hydrogen Interaction with Graphene, Graphene Hydroxide, and Lithiated Graphene S. Adak, A.I. Acatrinei, L.L. Daemen, B. Estes, M.H. Hartl, J.Z. Larese Neutron vibrational spectroscopy, together with adsorption isotherm measurements, has been employed to investigate interaction of hydrogen with graphene, hydroxylated graphene, and lithium incorporated graphene. The adsorption studies of hydrogen on these materials indicate varying degrees of hydrogen storage capacity. Graphene is found to have significantly higher hydrogen uptake than graphite and graphite oxide. Neutron vibrational spectroscopy provides direct information concerning hydrogen dynamics including the occurrence of the rotational mode at 119 cm-1; slightly below the free rotor position observed for H2 rotation on graphite. We have also explored how the interaction of hydrogen changes when hydroxyl groups are attached onto the graphene surface and when lithium is incorporated into graphene. The outcome of these studies will also be discussed. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W43.00005: Superpermeability of water through graphene based membranes Rahul Raveendran Nair, Rakesh Joshi, Hengan Wu, Jayaram Narayanan, Irina V. Grigorieva, Andre K. Geim Permeation through nanometre-pore materials has been attracting unwavering interest due to fundamental differences in governing mechanisms at macroscopic and molecular scales, the importance of water permeation in living systems, and relevance for filtration and separation techniques. One of the most spectacular findings in this field was the observation that carbon nanotubes and other hydrophobic nanocapillaries allow anomalously fast permeation of gases and liquids and, in particular, of water. In this contribution we show that membranes made from graphene oxide which are impermeable to liquids, vapours and gases, including helium, but allow unimpeded permeation of water (H$_{2}$O permeates through the membranes at least 10$^{10}$ times faster than He). We attribute these seemingly incompatible observations to a nearly frictionless flow of a monolayer of water through two dimensional capillaries formed by closely spaced graphene sheets. The flow is driven by a large capillary-like pressure and normally limited only by evaporation from the wetted surface of the membranes. The permeation can be stopped by either reducing graphene oxide or inducing a reversible drying transition in low humidity, which narrow nanocapillaries in both cases. I will also give an overview of our latest results on ion permeation through these membranes. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W43.00006: Quantification of crumpling in sheet-like nanostructures Peter Beaucage, Durgesh Rai, Gregory Beaucage, Siddharth Pradhan Two-dimensional sheet-like nanostructures have garnered significant scientific interest in recent decade, particularly due to their inherent high specific surface areas (SSAs). Such large SSAs also result in an intrinsic tendency to crumple or fold based on surface interactions under ambient conditions. An understanding of the topological details of such structures has revealed various qualitative features driven by thermodynamics and interfacial chemistry. A scaling model based methodology will be presented which can be utilized to do quantitative analysis using small angle scattering data. A wide range of materials like graphene oxide, membrane layers as well exfoliated sheets of molybdenum oxide and tungsten oxide have been investigated to understand how such quantification may yield a general classification of such materials based on crumpling behavior. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W43.00007: Concavity effects on the optical properties of aromatic hydrocarbons Marilia J. Caldas, Caterina Cocchi, Deborah Prezzi, Alice Ruini, Annalisa Fasolino, Elisa Molinari We address the modifications on the ground and excited state properties of polycyclic aromatic hydrocarbons (PAHs) induced by variations of concavity and $\pi$-connectivity. We study three series of PAHs, inspired by experimentally feasible systems, from hydrogen-saturated graphene flakes to concave ``buckybowls'' related to the formation of fullerene C$_{60}$ and carbon nanotube caps. We work within the framework of Hartree-Fock-based semiempirical methods (AM1 and ZINDO/S), and our results are supported by a generally good agreement with the available data. We see clearly that the interplay between concavity and $\pi$-connectivity shifts the bright optical lines to higher energies, and introduces symmetry-forbidden dark excitations at low energy [1]. These features can be the basis for designing optical properties of novel curved aromatic molecules.\\[4pt] [1] C. Cocchi et al. submitted (2012). [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W43.00008: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W43.00009: Giant Fullerenes for Target Specific Drug Delivery Robert Courtney, Boris Kiefer Carbon nano-structures, such as giant fullerenes, have a great potential for biological and medical applications. Most of the previous research is dedicated to investigate the use of fullerenes as vehicles for carrying medication which is chemisorbed on the outside surface of the fullerenes. In contrast, using fullerenes as an enclosure was largely abandoned due to the high strength of the carbon-carbon bonds which has been perceived to prevent the rupturing of the fullerene to release their cargo. We performed atomistic computations based on classical force fields that will address this perception. Specifically we explore the physics and chemistry of OH functionalized carbon based giant fullerenes with diameters from 0.72 nm (60 atoms) to 5.7 nm (3840 atoms). The preliminary results show that OH functionalization on these fullerenes is not only viable but also provides a pH sensitive release mechanism. Furthermore our current results show that carbon-carbon bonds can be broken in low energy biological environments in the presence of a flow induced strain field. These insights may have implications for target specific drug delivery in general and cancer treatment in particular. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W43.00010: Photo-Electron Injection into TiO2: Quantum Dot vs. Graphene Run Long We presented a detailed comparison on the similalaries and differences of the ultrafast photoinduced electron transfer (ET) from two kinds of donor species, namely PbSe quantum dot (QD) and graphene, into the acceptor TiO$_{2}$ surface via \textit{ab initio} time domain density functional theory simulations. The main diffrences stem from the size and dimensionality of the donor species and donor-acceptor bonding characteristics. For exmaple, the QD is localized species and composed by heavy atoms that connected to TiO$_{2}$ surface via chemical bonds. In contrast, the graphene layer is delocalized two-dimensional object that attached to TiO$_{2}$ substrate by van der Waals interaction and partial chemical bonds. The ET mechanism depends on the dimensionality of the donor and donor-acceptor chemical bonding. The injection from the localized donor states of the QD is dominatly adiabatic. In contrast, the injection from the two-dimensional graphene into TiO$_{2}$ exhibits prominently nonadiabatic (NA) component. The NA mechanism is efficient for the graphene/TiO$_{2}$ composites because it is delocalized over two dimensions and is able to couple with a dense manifold of delocalized TiO$_{2}$ conduction band states and weak coupling as well. The high density of acceptor states in this case favors the NA mechanism. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W43.00011: Lattice dynamics of cubic CaSiO$_3$ perovskite at high temperatures and pressures Tao Sun, Dong-Bo Zhang, Renata M. Wentzcovitch Cubic CaSiO$_{3}$-perovskite is a minor but important phase of the Earth's lower mantle. It is a mechanically unstable phase at low temperatures but it is stabilized at lower mantle temperatures. We have investigated its vibrational properties at high pressures and temperatures of the lower mantle. We have projected ionic velocities from ab initio molecular dynamics trajectories onto vibrational normal modes and computed the mode-mode correlation function from which we extract phonon frequencies and life times at finite temperatures. These correlations clearly indicate that normal modes with imaginary frequencies at 0 K are stabilized with increasing temperature. To overcome the finite size effect inherent in molecular dynamics simulations, a renormalized second-order force constant matrix in real space is constructed from the phonon frequencies at finite temperature and the phonon polarization vectors. Phonon dispersions and vibrational density of states are then determined by Fourier interpolation using the renormalized force matrix. These temperature dependent dispersions allow us to investigate thermodynamics and thermal elastic properties at lower mantle conditions. [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W43.00012: \textit{In situ} neutron diffraction study of SII CO deuterohydrate clathrate Jinlong Zhu, Shiyu Du, Xiaohui Yu, Hongwu Xu, Sven Vogel, Changqing Jin, Yusheng Zhao SII CO clathrate has been successfully synthesized at $\sim$ 100 bar and 252 K. During the synthesis process, SI CO clathrate was formed first as an intermediate phase and then transformed to SII clathrate. Structural parameters of SII CO clathrate at temperatures from 25 K to 260 K have been determined from Rietveld analysis of neutron diffraction data. With decreasing temperature, the decrease of lattice parameter can be described by a two-order polynomial thermal expansion equation. The molecular lengths of CO in the small and large cages decrease linearly with decreasing temperature. There is one CO molecule in each small cage, whereas two CO molecules occupy in each large cage. CO molecules are not localized at the cage centers. Rather, they exhibit disordered distributions in both small and large cages, while the CO in small cage shows a donut shape nuclear distributions around the cage center, the CO in large cage delocalized from the cage center and more disordered with increasing temperature. [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W43.00013: Study of growth mechanism and atomic structure of Au-Pd core-shell nanocube by Cs-corrected scanning transmission electron microscopy Nabraj Bhattarai, Gilberto Casillas, J. Jesus Velazquez Salazar, Arturo Ponce, Miguel Jose-Yacaman Au-Pd core-shell nanocubes of controlled sizes from 14 nm to 30 nm were synthesized using seed mediated growth process. The Pd shell layers were controlled from some monolayers to 10 nm. The stepwise growth mechanism from nucleation and growth of Au nanoparticles to final core-shell nanocube was studied by using conventional transmission electron microscopy (TEM) and Cs-corrected scanning transmission electron microscopy (STEM). It was found that the nanocubes grew from octahedral Au seeds due to fast growth along \textless 111\textgreater\ directions and concavity occurred because of high reduction rate of ascorbic acid (AA). The concave nanocube showed a change in strain-release mechanism as the Pd shell grew from a few layers to a 30 nm nanocube. Shockley partial dislocations (SPD), stacking faults (SF) and edge dislocations were found to be the mechanism to release the mismatch strain. The smallest size nanocube with HIFs will be suitable in order to maximize the catalytic activity per unit weight and mass specific activity. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W43.00014: Study of B1 (NaCl-type) to B2 (CsCl-type) pressure-induced structural phase transition in BaS, BaSe and BaTe using first-principles computations Sanjay Khare, Xiuquan Zhou, Jason L. Roehl, Cora Lind We have studied the pressure-induced phase transitions from NaCl-type (B1) to CsCl-type (B2) structure in BaS, BaSe and BaTe by using {\it ab initio} density functional theory computations in the local density approximation. The Buerger and WTM\footnote{M. Watanabe {\it et. al}, Acta Crystallogr., Sect. A {\bf 33}, 294 (1977).} mechanisms were explored by mapping the enthalpy contours in two and four dimensional configuration space for the two mechanisms, respectively. Transition pressures for BaS, BaSe and BaTe were determined to be 5.5 GPa, 4.9 GPa and 3.4 GPa, respectively. From these configuration space landscapes, a low enthalpy barrier path was constructed for the transitions to proceed at three different pressures. We obtained barriers of 0.18, 0.16 and 0.15 eV/pair (17.4, 15.4 and 14.5 kJ/mol) for the Buerger mechanism and 0.13, 0.13 and 0.12 eV/pair (12.5, 12.5 and 11.6 kJ/mol) for the WTM mechanism at the transition pressures for BaS, BaSe and BaTe, respectively, indicating that the WTM mechanism is slightly more favorable in these compounds. We describe the difference of the two mechanisms by differences in their symmetry and atomic coordination. [Preview Abstract] |
Thursday, March 21, 2013 5:18PM - 5:30PM |
W43.00015: The quasi-Bragg law, transforming the icoshedral diffraction pattern onto a hierarchic structure Antony Bourdillon Previously, we have demonstrated [1]: 1) The golden section $\tau $ is as fundamental to the icosahedral structure (length /edge) as $\pi $ is to the sphere (circumference /diameter). 2) The diffraction series are in restricted Fibonacci order because the ratio of adjacent terms $f_{n}/f_{n-1}$ does not vary, but is the constant $\tau $. The series is therefore geometric. 3) The matrix fcc Al is an approximant for i-Al$_{6}$Mn. 4) A three dimensional stereographic projection and a quasi-Bragg law are derived, correctly representing the diffraction series in powers of $\tau $ [2], without redundancy. 5) By the normal conventions of electron microscopy, the diffraction patterns are completely indexed in three dimensions. Now we describe significant consequences: 1) The diffraction pattern intensities near all main axes are correctly simulated, and all atoms are located on a specimen image. 2) The quasi-Bragg law has a special metric that we have measured. Atomic locations are consistently calculated for the first time. 3) Whereas the Bragg law transforms a crystal lattice into a reciprocal lattice in diffraction space, the quasi-Bragg law transforms a geometric diffraction pattern into a hierarchic structure. 4) Hyperspatial indexation [3] is superceded.\\[4pt] [1] Bourdillon, A.J., APS conference, Louis Obispo, Nov. 2-3 2012.\\[0pt] [2] Bourdillon, A. J.,\textit{ Sol. State Comm.} \textbf{2009}, 149, 1221-1225.\\[0pt] [3] Duneau, M., and Katz, A., \textit{Phys Rev Lett} \textbf{54}, 2688-2691 [Preview Abstract] |
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