Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y16: Fullerenes and Composites |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Rajendra Zope, University of Texas at El Paso Room: B115 |
Friday, March 19, 2010 8:00AM - 8:12AM |
Y16.00001: Structural and magnetic properties of Tc$_n$@C$_{60}$ endohedral metallofullerenes: An {\em ab initio} study Eunja Kim, Philippe F. Weck, Kenneth R. Czerwinski, David Tom\'anek We use {\em ab initio} spin density functional calculations to study the equilibrium structure and magnetic properties of Tc$_n$@C$_{60}$ endohedral metallofullerenes. The radionuclide $^{99{\rm m}}$Tc is well established in biomedicine as a potent {\em in vivo} diagnostic radiopharmaceutical; its encapsulation in the inert C$_{60}$ shell is expected to limit possible cytotoxicity of radiometal nanoparticles catabolized by the biological host. We find that C$_{60}$ can endohedrally accommodate Tc$_n$ clusters with up to $n=7$. The encapsulation does not change significantly the structure of the enclosed clusters, but reduces the magnetic moment due to a stronger Tc--C hybridization for the larger clusters. [Preview Abstract] |
Friday, March 19, 2010 8:12AM - 8:24AM |
Y16.00002: ABSTRACT HAS BEEN MOVED TO S1.00091 |
Friday, March 19, 2010 8:24AM - 8:36AM |
Y16.00003: Electronic Transport in B- and N-doped Fullerenes: BC$_{59}, $BC$_{60}$, NC$_{59 }$ and NC$_{60}$ Xiaoliang Zhong, Ravindra Pandey, Alexandre Rocha, Shashi Karna The electron transport via boron and nitrogen doped fullerenes (i.e. BC$_{60}$, NC$_{60}$, BC$_{59}$ and NC$_{59})$ are studied using first principles methods coupled with non-equilibrium Green's Function formalism. The predicted conductivity for the doped fullerene is higher than that of the pristine fullerene. A substantial conduction is predicted for BC$_{59}$ at higher bias voltage of $>$1.0 V. The hybrid states near the Fermi region involving contact gold atoms appear to play an important role in determining the conductivity of these systems. [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 8:48AM |
Y16.00004: Investigation of Gd$_{3}$N@C$_{2n}$ (40 $\leq$ $n$ $\leq$ 44) family by Raman and inelastic electron tunneling spectroscopy Brian Burke, Jack Chan, Keith Williams, Jiechao Ge, Chunying Shu, Wujun Fu, Harry Dorn, James Kushmerick, Alexander Puretzky, David Geohegan The structure and vibrational spectrum of Gd$_{3}$N@C$_{80}$ is studied through Raman and inelastic electron tunneling spectroscopy (IETS) as well as density functional theory (DFT) and universal force field (UFF) calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd$_{3}$N$-$C$_{80}$ bond which reduces the ideal icosahedral symmetry of the C$_{80}$ cage. The vibrational modes involving the movement of the encapsulated species are a fingerprint of the interaction between the fullerene cage and the core complex. We present Raman data for the Gd$_{3}$N@C$_{2n}$ (40 $\leq$ $n$ $\leq$ 44) family as well as Y$_{3}$N@C$_{80}$, Lu$_{3}$N@C$_{80}$, and Y$_{3}$N@C$_{88}$ for comparison. Conductance measurements have been performed on Gd$_{3}$N@C$_{80}$ and reveal a Kondo effect similar to that observed in C$_{60}$. [Preview Abstract] |
Friday, March 19, 2010 8:48AM - 9:00AM |
Y16.00005: The structures of a C$_{60}$ monolayer on Au(111) Heekeun Shin, Katariina Pussi, Renee Diehl, Ajay Shukla, Vincent Fournee, Julian Ledieu The in-phase and (2$\surd $3x2$\surd $3)R30\r{ } structures of monolayer C$_{60}$ on Au(111) have been studied by scanning tunneling microscopy and dynamical low energy electron diffraction. The in-phase domains exhibit a (2x2) superlattice in high resolution STM images at 57K, in which one of the four molecules in the unit cell has a three-lobe intramolecular shape. After annealing at 663K, most of the monolayer was converted to R30\r{ } domains. The C$_{60}$ molecules in the (2$\surd $3x2$\surd $3)R30\r{ } domains image as random bright or dim objects, with a 50:50 ratio of bright to dim. At room temperature, there are conversions from bright to dim and vice versa, but such conversions are suppressed at 57K. The dynamical LEED analysis of (2$\surd $3x2$\surd $3)R30\r{ } structure will be presented. [Preview Abstract] |
Friday, March 19, 2010 9:00AM - 9:12AM |
Y16.00006: Surface Geometry of $\mathrm{C}_{60}$ on Ag(111) Hsin-I Li, Katariina Pussi, Julian Ledieu, Heekeun Shin, Renee Diehl The geometry of adsorbed $\mathrm{C}_{60}$ influences its collective properties. We report the dynamical low-energy electron diffraction and scanning tunneling microscopy studies to determine the geometry of a $\mathrm{C}_{60}$ monolayer, Ag(111)-($2\sqrt{3}\times 2\sqrt{3}$)$30\,^{\circ}$-$\mathrm{C}_{60}$ and related density functional theory calculations. The stable monolayer has $\mathrm{C}_{60}$ molecules in vacancies that result from the displacement of surface atoms. $\mathrm{C}_{60}$ bonds with hexagons down, with their mirror planes parallel to that of the substrate. The results indicate that vacancy structures are the rule rather than the exception for $\mathrm{C}_{60}$ monolayers on close-packed metal surfaces and closely related to the anneal. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:24AM |
Y16.00007: Low temperature Scanning Tunneling Spectroscopy of C60 films on the Cu(100) surface David R. Daughton, Nancy M. Santagata, Jay A. Gupta In contrast to other single crystal metal surfaces, C60 adopts four unique orientations on the Cu(100) surface. The intramolecular structure of C60 stabilized in monolayer films on a Cu(100) surface has been studied with low temperature (5 K) scanning tunneling microscopy and spectroscopy. We present the first spectroscopy and spatial imaging of molecular orbital resonances from LUMO to LUMO+3 for the four distinct adsorption geometries. Shifts in the LUMO state indicate different degrees of charge transfer for the four geometries. We aim to correlate changes in C60 electronic structure with chemical modification via electron-induced polymerization. Density functional theory (DFT) computations of the C60/Cu(100) system have been carried out in support of the experimental results. [Preview Abstract] |
Friday, March 19, 2010 9:24AM - 9:36AM |
Y16.00008: Ca coated boron nanostructures: Energetics and possible usage for hydrogen storage Tunna Baruah, Marco Olguin, Rajendra Zope We investigate the adsorption of calcium atoms on the surface of novel boron fullerenes and the alpha boron sheet using density functional theory within the generalized gradient approximation. Recent theoretical works show that the B$_{80}$ fullerene coated with one Ca atom on each pentagonal ring is capable of storing up to 60 H$_2$ molecules, yielding a gravimetric density of 8.2 wt.\%. We have performed a detailed investigation of Ca adsorption on the B$_{80}$ fullerene. In contrast to recent results, our calculations show that a single Ca atom prefers to occupy a hexagonal site rather than a pentagonal site. The calculations on Ca$_{12}$B$_{80}$, Ca$_{20}$B$_{80}$ and Ca$_{32}$B$_{80}$ indicate that Ca atoms prefer to uniformly coat the whole surface over selectively occupying the pentagonal or hexagonal sites. We have examined the feasibility of H$_2$ storage on Ca$_{32}$H$_{80}$ in the range 7.2 - 8.2 wt\%. Our calculations indicate that the uniformly coated Ca$_{32}$B$_{80}$ fullerene is not capable of achieving a hydrogen storage capacity of 7.2 wt. \% or higher. It is necessary to somehow reduce the Ca concentration on the B$_{80}$ surface to achieve a 8.2 wt. \% of hydrogen. [Preview Abstract] |
Friday, March 19, 2010 9:36AM - 9:48AM |
Y16.00009: Analytical Description of Asymmetric Reflectance in Percolation Films Nicholas Kuhta, Viktor Podolskiy, Aiqing Chen, Keisuke Hasegawa, Miriam Deutsch We develop a quantitative description of giant asymmetry in reflectance, recently observed in semicontinuous metal films. The developed scaling-theory-based technique adequately explains the spectral properties of semicontinuous composites, as well as provides insight into the origin of an experimentally observed absorbance anomaly in the vicinity of percolation threshold. Scaling theory suggests that the origin of the anomalous minimum in absorbance at the percolation threshold lies in the dramatically reduced correlation length in our solution-derived films as compared to their vacuum-deposited counterparts. The latter phenomenon is consistent with the restriction of the electron mean free path, often observed in solution-derived plasmonic nanostructures. [Preview Abstract] |
Friday, March 19, 2010 9:48AM - 10:00AM |
Y16.00010: Elastic Waves in the Porous Materials, Sizing of the Inhomogenieties. Hasson M. Tavossi Theoretical models for porous materials include porosity as an input parameter and not the average pore size, among other factors. It has been shown that porous materials with the same porosity but different average pore sizes can have very different elastic wave properties. Experimental results show that average pore-size has a significant effect on both wave attenuation and pass-band frequencies of the porous materials having the same porosities. Most porous materials with open pores act as pass-band filters for the transmitted elastic waves. Experimental results are obtained for elastic wave frequency filtering and attenuation as a function of average pore size and frequency, for materials of the same porosity. Pass-band and attenuation is expressed as a function of the average pore size, when other material properties are kept constant. Inhomogenieties are introduced in the material as defect and their effects on transmitted wave dispersion, attenuation and pass band are analyzed. The goal of this research is to determine size and location of inhomogenieties or defects in the porous materials from the transmitted wave spectrum. [Preview Abstract] |
Friday, March 19, 2010 10:00AM - 10:12AM |
Y16.00011: Energy transfer of dye molecule-containing zeolite monolayer studied using polarized photoluminescence spectroscopy Hyunjin Lim, Hyeonsik Cheong, Jin Seok Lee, Kyung Byung Yoon The inter- and intra-molecule energy transfers in dye molecules in zeolite crystals were studied using polarized photoluminescence spectroscopy. We used nanoporous zeolite L crystal and two kinds of dye molecules, pyronine B (PyB) and Y (PyY), as the host and guest materials, respectively. The dye- containing zeolite monolayer was vertically oriented to the substrate. From the depolarization ratio, we can confirm that the PyB are tightly confined and line up along the channel direction of the zeolite. On the other hand, PyY is smaller than PyB and can be positioned perpendicular to the channel direction of the zeolite. The luminescence of PyB embedded in zeolite pores was blue-shifted, but that of PyY embedded in zeolite pores was not changed compare to the dye molecules in solvent. When the polarization direction of the incident beam was perpendicular to the c-axis of zeolite monolayer, a red- shift relative to the parallel polarization case was observed. This result shows the energy transfer from intra-channel dye molecules to the dye molecules outside the pores. The depolarization ratio of the PyY-containing zeolite monolayer was lower than that of randomly dispersed PyY molecules in solvent. From this, we infer that there is an inter-molecule energy transfer inside the zeolite pores. [Preview Abstract] |
Friday, March 19, 2010 10:12AM - 10:24AM |
Y16.00012: Effects of Loading Mode, Pore Morphology, and Thermal Treatment on the Mechanical Behavior of Ultra-Low-Dielectric-Constant Mesoporous Amorphous Silica Films M. Rauf Gungor, James Watkins, Dimitrios Maroudas We present a systematic molecular-dynamics analysis of the mechanical behavior of regular mesoporous amorphous silica structures with ultra-low dielectric constants under various modes of applied straining within the elastic limit near room temperature. We examine structures with spherical and cylindrical pores of nanometer-scale diameters. We compute the elastic moduli of the mesoporous structures and analyze their structural stability under tensile and compressive straining as a function of density and pore diameter. We find that the elastic moduli decrease with decreasing pore size and derive modulus-density relationships. The mesoporous films are generally stronger under tensile than compressive straining. The strength of films with cylindrical pores depends on the mechanical loading direction with respect to the pore axes. Thermal treatment of the mesoporous structures below the glassy transition temperature leads to a mild increase of their elastic moduli. [Preview Abstract] |
Friday, March 19, 2010 10:24AM - 10:36AM |
Y16.00013: ABSTRACT WITHDRAWN |
Friday, March 19, 2010 10:36AM - 10:48AM |
Y16.00014: Elucidation of the Microstructure of Carbon-Carbon Composites by Raman Microscopy Sergey Mamedov, Fran Adar, Eunah Lee, Andrew Whitley Carbon-carbon composites are used in aerospace materials as well as some automotive, high-end sports and helmet applications. Their advantages include stiffness, strength, and light weight. Because of the importance of their applications, especially in aerospace, any technique that can characterize them is of interest. Images of a composite created on Raman microscope has been used to characterize a carbon-carbon composite. It is shown the information is encoded in both details of the spectral features and polarization behavior. Polarized Raman maps were collected using the 633nm laser and the 300g/mm grating. At each point in the map there is a spectrum that includes the G mode, the D mode (when present) and the overtone and combination bands between 2400 and 3300 cm$^{-1}$. Using multivariate techniques to extract information from the hyperspectral cube, it was possible to create Raman images where the fibers and the matrix carbon are differentiated, even though the spectral differences are quite subtle. Correlations between the polarized Raman images and standard polarized light microscopy enables determination of the orientation of the graphite planes in the matrix which can effect the physical properties of the composite. [Preview Abstract] |
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