Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A32: Fullerenes |
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Sponsoring Units: DCMP Chair: Tunna Baruah, University of Texas, El Paso Room: Baltimore Convention Center 329 |
Monday, March 13, 2006 8:00AM - 8:12AM |
A32.00001: The measuring the conductance of carbon fullerene and onion. Makoto Yoshida, Yoshihiko Kurui, Yoshifumi Oshima, Kunio Takayanagi In this study, we simultaneously observed the conductance and the structure of carbon nano-materials (C60 and carbon onion) using transmission electron microscopy(TEM). This TEM is combined with scanning tunneling microscope (STM) system. C60 and carbon onion was fabricated and sandwiched between two gold electrodes of STM. As a results, the C60 and carbon onion show a metallic conductance (the same order magnitude of 2e$^{2}$/h) at the low bias. These values are near to results of previous theoretical reports. Further more, we obtained the conductance variation which is strongly affected by the connection between the C60 and metal electrodes. [Preview Abstract] |
Monday, March 13, 2006 8:12AM - 8:24AM |
A32.00002: On the zero-bias anomaly in K-doped $C_{60}$ on Ag(100) Noah Bray-Ali, Amy Khoo, Jeffrey Neaton, Steven Louie, Ryan Yamachika, Andre Wachowiak, Michael Crommie, Joel Moore The fullerene molecule $C_{60}$ is known to undergo a strong Jahn-Teller distortion when electrons are added. Recent STM/STS experiments indicate that a single $C_{60}$ molecule on a Ag(100) surface can be controllably doped with charge-donating potassium atoms;~[1] moreover, the experiments suggest that the molecular electronic structure can be tuned so that a single electronic orbital lies near the Fermi level. Starting from a Hamiltonian with parameters inferred from companion density functional theory (DFT) calculations of $K_{x}C_{60}$ on Ag(100), we use Wilson's numerical renormalization group to compute the spectrum near the Fermi level of a doped $C_{60}$ molecule coupled to a metallic continuum. The result compares favorably with spectroscopic measurements of the zero-bias anomaly and, together with the DFT calculations, explains the electronic structure of this system over a range of dopings. \newline \newline [1] R. Yamachika, M. Grobis, A. Wachowiak, and M.F. Crommie, {\it Science} {\bf 304}, 281-284 (2004). [Preview Abstract] |
Monday, March 13, 2006 8:24AM - 8:36AM |
A32.00003: Ab initio modeling of STM elastic and inelastic tunneling spectra of tetramantane on Au(111) surface. Emmanouil Kioupakis, R. Yamachika, Y. Wang, X.H. Lu, M.F. Crommie, Steven G. Louie The recent discovery of the higher diamondoids in crude oil has stimulated interest in their study and several potential technological applications of these molecules have already been proposed. In studying the electronic properties of molecular or nanoscale structures on surfaces, the scanning tunneling microscope is usually the probe of choice. Currently, scanning tunneling microscopy experiments of isolated tetramantane molecules on a (111) gold surface are being carried out. We have performed ab initio pseudopotential density functional theory calculations of the electronic properties of tetramantane and provide a comparison of the elastic and inelastic tunneling spectra between our simulation and the ongoing experiment. This work was supported by the NSF Grant Nos. DMR04-39768 and EEC-0425914 and U.S. DOE Contract No. DE-AC03-76SF00098. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A32.00004: Anomalous electric conductivity in C60-Ag co-deposited films at low temperature Genki Yoshikawa, Yuki Tsuruma, Susumu Ikeda, Koichiro Saiki The C60-Ag interface has attracted interest recently. In addition to charge transfer from Ag to C60 or metallization of C60, temperature dependent gap was observed at the Fermi level of the C60 monolayer on Ag, suggesting the possibility of interfacial superconductivity. In order to clarify the effect of this interfacial electronic state on the transport properties, we measured the electric conductivity of the C60-Ag complex films. To increase the interface area, Ag and C60 were co-deposited on the insulating substrate, such as mica, maintained at 23 K, suppressing the aggregation of Ag atoms. The electric conductivity of the C60-Ag co-deposited films was measured in-situ in a temperature range of 23-300 K. Two peaks were observed in the conductivity curve around 50 K and 85 K. They disappeared once the film was annealed up to room temperature. This phenomenon was observed when the Ag/C60 ratio is approximately 1 to 6 while we studied in the range of 0.5-20. We confirmed that these peaks were not caused by the influence of Joule heating or residual gases. The observed anomalous electric conductivity strongly suggests the formation of peculiar structure and electronic states in the films at low temperature. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A32.00005: Novel orientational ordering in a K-doped C$_{60}$ monolayer Ryan Yamachika, Yayu Wang, Andre Wachowiak, Michael Grobis, Dung-Hai Lee, Amy Khoo, Steven Louie, Michael Crommie Orientational ordering, which originates from broken rotational symmetry, is a central feature of a broad range of materials including liquid crystals, quantum magnets, and some biological systems. By doping C$_{60}$ monolayers with alkali impurities, the symmetry of C$_{60}$ molecules can be broken, opening up the possibility for unique two-dimensional molecular orientational ordering. Here we present a scanning tunneling microscopy/spectroscopy study of K$_{x}$C$_{60}$ monolayers on Au(111), $x\ge $4. We find novel orientational orderings in the C$_{60}$ monolayers at different doping levels, which coincide with strong variations in the monolayer local density of states. This demonstrates the importance of the interplay between Coulomb repulsion, electron-phonon coupling, electronic quadrupolar interactions, and direct orbital overlap in determining the behavior of fullerene nanostructures. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A32.00006: Study of Trapping Sites for Beryllium Atom in C$_{60}$-Fullerene and Electron Capture for $^{7}$Be Nucleus. Lee Chow, Archana Dubey, Gary S. Collins, R.H. Scheicher, R.H. Pink, Dip N. Mahato, T.P. Das First-Principles Hartree-Fock studies of Be atom in C$_{60 }$-fullerene are being carried out for the trapping sites and electron densities at the $^{7}$Be nucleus for these sites, the latter expected to be helpful for understanding the significantly higher electron capture rate for $^{7}$Be as compared to a number of other materials experimentally studied including graphite [1]. Possible trapping sites including those found from Hartree-Fock investigations [2] on muonium (H atom) and additional ones above and below the surface perpendicular to C-C bond centers are being investigated. Results will be presented and discussed. \newline \newline [1] T. Ohtsuki et al, Phys. Rev. Lett. 93, 112501-1 (2004) and references therein. \newline [2] O. Donzelli, T. Briere and T.P. Das, Sol. St. Comm. 90, 663(1994); Indian J. Phys. 67(Spec. Issue), 35(1993). [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A32.00007: Novel Silicon-Carbon Nanostructures: A DFT Study on the Stability of Si$_{60}$C$_{2n}$ (n= 3, 10, 12) Clusters. A. Srinivasan, M.N. Huda, A.K. Ray In this work, we extend our previous work on Si$_{60}$C$_{2n}$ (n=1, 2) clusters by the addition of six, twenty and twenty-four carbon atoms on the surfaces of the Si$_{60}$ cages by substitution and inside the cage at various symmetry orientations [1]. The theoretical formalism used is the generalized gradient approximation to density functional theory and full geometry and spin optimizations have been performed using the Gaussian 03 software. For the silicon atom, the Hay-Wadt pseudo-potential with the associated basis set is used for the core and the valence electrons, respectively. For the carbon atom, the Dunning/Huzinaga double zeta basis set is employed. Different electronic properties of these nanostructures will be discussed in detail. The binding energy per atom for these nanostructures increases with the number of carbon atoms, with the structures having carbon atoms on the surface being more stable. The stability of the nanostructures depends on the orientation of the carbon atoms, as well as on the natures of Si-C and C-C bondings. [1] A. Srinivasan, M. N. Huda and A. K. Ray, Phys. Rev. A, in press; A. Srinivasan and A. K. Ray, J. Nanosci. and Nanotech., in press. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A32.00008: What is the Goundstate Structure of Intermediate-sized Carbon Clusters? M. Yu, I. Chaudhuri, C.S. Jayanthi, S.Y. Wu Recent study on the equilibrium structures of quantum dots of tetravalent semiconductors such as Si clusters revealed that the ground state structures of these clusters with diameters d$<$5 nm are icosahedrons comprising of tetrahedral building blocks rather than corresponding bulk-truncated clusters[1]. Among tetravalent semiconductors, carbon is the only element whose atoms could form sp, or sp$^{2}$ or sp$^{3}$ bonding configurations, leading to compact, fullerene, and bucky-diamond clusters[2]. It is then natural to raise the question as to what is the ground-state structure for the carbon cluster C$_{n}$ for a given $n \quad \ge $ 20? We have recently initiated a preliminary study on the relative stability of carbon clusters C$_{n}$ with $n $up to 700, using a molecular dynamics scheme based on a self-consistent and environment-dependent Hamiltonian developed at the U. of Louisville in the framework of the linear combination of atomic orbitals[3]. Our preliminary result indicates that in the range of $n$ studied, the carbon fullerene clusters are still the most stable clusters, in contrast to the icosahedral cluster being the ground state structure for a series of discrete $n$ values for the other tetravalent clusters. We will also discuss the other electronic properties of intermediate-sized carbon clusters. This work was supported by the U.S. DOE (DE-FG02-00ER4582). [1] Y. Zhao, \textit{et al}\textbf{\textit{.,}} Phys. Rev. Lett. \textbf{93}, 015502 (2004). [2] J. Y. Raty, \textit{et al.}\textbf{\textit{,}} Phys. Rev. Lett. \textbf{90}, 037401 (2003). [3] S.Y. Wu, \textit{et. al}., \textit{Handbook of Materials Modeling }Vo.\textbf{l,} p.2935 (2005). [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A32.00009: Electronic structure and electron-phonon coupling in carbon diamondoids studied by scanning tunneling microscopy Yayu Wang, X.H. Lu, R. Yamachika, A. Wachowiak, E.S. Kioupakis, S.G. Louie, M.F. Crommie, J.E. Dahl, S.G. Liu, R.M.K. Carlson Diamondoids are hydrocarbon molecules with diamond-like cage structures. Their structural complexity and chemical bond tunability make them ideal building blocks for creating novel nanostructures. We have used cryogenic scanning tunneling spectroscopy to examine the electronic structure of individual diamondoid molecules on the Au(111) surface. We observed variations in the filled and empty state local density of states for individual 121-tetramer diamondoid molecule. Despite a large HOMO-LUMO gap ($\Delta \quad >$ 5eV) around the Fermi energy, there exists a strong interaction between the tunneling electrons and the diamondoid C-H stretch mode, as revealed by inelastic tunneling spectroscopy (IETS). We further show that the strength of the electron-phonon coupling has a distinct spatial distribution with the dominant inelastic channel localized to a specific region of the diamondoid molecule. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A32.00010: NMR Probes of the Molecular Orientational Dynamics of the Endohedral Fullerene Sc$_{3}$N@C$_{80}$. Joe Martindale, Krzysztof Gorny, Charles Pennington, Page Phillips, Steven Stevenson We report NMR lineshapes and spin-lattice relaxation times for both $^{13}$C and $^{45}$Sc in the endohedral fullerene Sc$_{3}$N@C$_{80}$. The data show rapid reorientation of the molecule with an activated temperature dependence for the motion over the observed temperature range (50 -- 350 K). The ratchet to rotator transition found in C$_{60}$ is not observed in Sc$_{3}$N@C$_{80}$. The measurements strongly suggest the motion of the encapsulated Sc$_{3}$N derives from the reorientational dynamics of the C$_{80}$ cage, however without the Sc$_{3}$N being fixed to the cage in the motional narrowing regime. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A32.00011: Towards Implementation of a Solid State Quantum Computer Based on Endohedral Fullerenes D.V. Pelekhov, P. Banerjee, I.H. Lee, K.C. Fong, Yu. Obukhov, J. Martindale , P. C. Hammel, J.P. Phillips , S. Stevenson We report on progress investigating the feasibility of fabricating a Solid State Quantum Computer based on endohedral fullerenes (fullerenes containing species with unpaired electron spins). The results of experiments on endohedral fullerene systems using Magnetic Resonance Force Microscopy, conventional Electron Spin Resonance and Scanning Tunneling Microscopy will be presented. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A32.00012: Quasi Small-World Nanomaterials : Quantum Studies M.A. Novotny, Jeremy Yancey, Steven Gwaltney, Serkan Caliskan We present results for two studies of quasi-small-world nanomaterials [1,2]. These are materials that would have the connectivity governed by small-world (SW) networks. Hence these materials should have both their critical behavior and transport properties governed by mean-field fixed points, not finite-dimensional fixed points. One study utilizes density-functional-theory to obtain reasonable carbon-based molecules that should have the SW property. In particular, several candidates for quasi- SW nanomaterials (or molecules) based solely on carbon will be presented. Trends in the energy per atom of various types of SW nanomaterials and numbers of carbon atoms will be presented. The transmission coefficient and conductivity for related quantum models of SW nanomaterials connected to metal leads will also be presented. [1] M.A. Novotny, et al, J. Appl. Phys, vol. 97, p.10E510 (2005). [2] M.A. Novotny and S.W. Wheeler, Brazilian J. Phys., vol. 34, p. 395 (2004). [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A32.00013: Dynamics of Bulk vs. Nanoscale WS$_2$: Local Strain and Charging Effects J. L. Musfeldt, S. Brown, R. D. Luttrell, J. Cao, R. Rosentsveig, R. Tenne We measured the infrared vibrational properties of bulk and nanoparticle WS$_2$ in order to investigate the structure- property relations in these novel materials. In addition to the symmetry-breaking effects of local strain, nanoparticle curvature modifies the local charging environment of the bulk material. Performing a charge analysis on the \emph{xy}-polarized E$_{1u}$ vibrational mode, we find an approximate 1.5:1 intralayer charge difference between the layered 2H material and inorganic fullerene-like (IF) nanoparticles. This effective charge difference may impact the solid-state lubrication properties of nanoscale metal dichalcogenides. [Preview Abstract] |
Monday, March 13, 2006 10:36AM - 10:48AM |
A32.00014: Collective excitations in concentric metallic nanoshells Shyamalendu Bose, Edward Zale Invention of nanoshells made of a silica core coated with an ultra-thin metallic layer [1] has opened a floodgate of many applications in medical and other fields. Most of these applications are triggered by the fact that the nanoshells have unusual electronic and optical properties which can be controlled by controlling the inner and outer radii of the nanoshell. Employing a classical hydrodynamic model, we have obtained a general expression for the resonant frequencies (plasmons) of the electrons for N concentric nanoshells. Results obtained using this theory will be compared with previous calculations for two concentric nanoshells [2] and possible applications of the new results will be discussed. 1. S.J. Oldenburg, \textit{et al}., Chem. Phys. Letts. \textbf{288}, 243 (1998). 2. E. Prodan, \textit{et al}.., Science \textbf{302}, 419 (2003). [Preview Abstract] |
Monday, March 13, 2006 10:48AM - 11:00AM |
A32.00015: A $^{13}$C NMR Spectroscopic Investigation of Carbon Nanohorns Hideto Imai, Panakkattu Babu, Eric Oldfield, Andrzej Wieckowski, Daisuke Kasuya, Takeshi Azami, Yuichi Shimakawa, Masako Yudasaka, Yoshimi Kubo, Sumio Iijima $^{13}$C NMR spectroscopic investigation of carbon nanohorn aggregates (CNH) shows that they consist of two components, characterized by different chemical shifts and spin-lattice relaxation (T$_{1})$ behavior. The first component with a chemical shift of 124 ppm and faster T$_{1}$ is assigned to the nanotube-like horns on the particles' surface. The second component with a chemical shift of 116 ppm and much slower T$_{1}$ is assigned to the graphite-like part of the CNH. Integrated peak area measurements indicate a 1:2 ratio of nanohorns to the graphite-like substrate. The lack of a Knight shift and the absence of a clear Korringa relaxation for either component of T$_{1}$ ruled out any metallic behavior and indicate a relaxation behavior characteristic of semiconducting materials with paramagnetic centers arising from structural defects. We also observed an anomalous change in T$_{1}$ in the nanohorn domains near 17 K, suggesting the development of an antiferromagnetic correlation between localized electron spins. [Preview Abstract] |
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