Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session S24: Fullerenes (not nanotubes) |
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Sponsoring Units: DCMP Chair: Dan Finkenstadt, Naval Research Laboratory Room: Morial Convention Center 216 |
Wednesday, March 12, 2008 2:30PM - 2:42PM |
S24.00001: Magnetic molecules made of nitrogen or boron-doped fullerenes Chih-Kai Yang By using density functional theory we investigate the electronic structure of a fullerene C60 molecule doped with nitrogen atoms. We find that as long as the number of the impurity atoms is odd the doped fullerene turns magnetic, with its magnetic moment determined by the way the impurities are bonded with the carbon cage. For even number of impurities the pairing of the electrons exclude the appearance of magnetism. Similar results also apply to fullerenes doped with boron. This simple way of creating single molecular magnets should be useful for the application in magnetic detection, quantum information, and spintronics. [Preview Abstract] |
Wednesday, March 12, 2008 2:42PM - 2:54PM |
S24.00002: Electron-phonon coupling in C$_{60}$ using exact-exchange functional Jonathan Laflamme Janssen, Michel C\^ot\'e The superconductivity in C$_{60}$ doped crystals is now well understood as a phonon mediated interaction. The strength of the electron-phonon coupling can be deduced by Raman and PES measurements which can then be used to assess the density-functional theory results. Although experimental and computed electron-phonon coupling agree on the total magnitude of the coupling, they do not on the contributions of the individual vibrational modes. Density-functional theory calculations indicate that high frequency modes are responsible for most of the coupling whereas experiments suggest that low frequency modes are the dominating contribution. Up to now, only calculations using the local density approximation (LDA) were performed. In this study, we investigate the effect of exact-exchange functionals, such as B3LYP, on the computed electron-phonon coupling of the different vibrational modes. [Preview Abstract] |
Wednesday, March 12, 2008 2:54PM - 3:06PM |
S24.00003: Electron Transfer and Localization in Endohederal Metallofullerenes Shenyuan Yang, Mina Yoon, Christian Hicke, Zhenyu Zhang, Enge Wang Endohedral metallofullerenes constitute an appealing class of nanoscale building blocks for fabrication of a wide range of noval materials. One open question of fundamental importance is the precise nature of charge redistribution with the carbon cages (C$_{n})$ upon metal encapsulation. Using ab initio density functional theory, we systematically study the electronic structure of metallofullerenes, focusing on the spatial charge redistribution. For all large metallofullerenes ($n>$32), the valence electrons of the metal atoms are all transferred to the fullerene states. Surprisingly, the transferred charge is found to be highly localized inside the cage near the metal cations, rather than uniformly distributed on the surfaces of the carbon cage as traditionally belied. This counterintuitive charge localization picture is attributed to the strong metal-cage interactions within the systems. These findings may prove to be instrumental in the design of novel fullerene-based functional nanomaterials. [Preview Abstract] |
Wednesday, March 12, 2008 3:06PM - 3:18PM |
S24.00004: Light Alkaline-Earth-Metal Coated Carbon Fullerenes as Effective Hydrogen Storage Media Mina Yoon, Shenyuan Yang, Christian Hicke, Enge Wang, David Geohegan, Zhenyu Zhang We propose functionalizing carbon nanostructures with light alkaline-earth metals for use as hydrogen storage media. To support this idea, we investigate the feasibility of coating C$_{60}$ fullerenes with light alkaline-earth metals and analyze the hydrogen storage capacities of the resulting compounds. We find a new and unique binding mechanism responsible for the strong binding between Ca or Sr atoms and C$_{60}$. Our theory explains experiments showing that C$_{60}$ can be evenly covered by a monolayer of Ca or Sr atoms. The coating results in a charge redistribution leading to electric dipolar fields around the metal atoms through which the fullerene surface becomes an ideal hydrogen-attractor with a binding strength larger than that of alkali carbon complexes but small enough to prevent hydrogen dissociation as in the case of transition metal decorated fullerenes. With a hydrogen uptake of more than 8.4wt\% and a binding energy of $\approx$ 0.4eV/H2 on C$_{60} $C$_{32}$ Ca is superior to currently used coating elements. [Preview Abstract] |
Wednesday, March 12, 2008 3:18PM - 3:30PM |
S24.00005: An Investigation of Magnetic, Electronic and Structural Properties of Metallofullerenes S. Vincent Ong, Meichun Qian, Shiv Khanna Gadolinium based endohedral metallofullerenes Gd$_{3}$N@C$_{80}$ functionalized with OH radicals have been found to enhance the relaxivity by orders of magnitude over conventional agents and are being sought as new contrast agents in magnetic resonance imaging (MRI). Using state of the art density functional theory (DFT) in the regime of the local density approximation with the on-site Coulomb interaction (LSDA+U), we have carried out theoretical studies to determine the electronic and magnetic properties of gadolinium-based and lutetium-based nitride fullerenes, namely Lu$_{3-x}$Gd$_{x}$N@C$_{80}$ (x = 1-2). While Gd$_{3}$N@C$_{80}$ has previously shown promising features as a contrast agent, the idea of replacing gadolinium atoms by lutetium has been proposed to result in a mixed-metal species for multi-modal imaging. Our results indicate that Lu$_{2}$GdN@C$_{80}$ is the most stable of all possible configurations with a binding energy 16.57 eV, can be considered for use as both an MRI contrast agent, due to gadolinium's high magnetic moment, and as a potential radioactive therapeutic or diagnostic agent, by neutron activation of a lutetium radioisotope. These results along with details of electronic structure will be presented. [Preview Abstract] |
Wednesday, March 12, 2008 3:30PM - 3:42PM |
S24.00006: First-Principles Investigation of C$_{60}$-Pd Interface Lan Li, Hai-Ping Cheng Conductivity and hybridization of C$_{60}$-Pd nano-system have been investigated using density functional calculations. From analysis of geometry, energetics and electronic structures, the interaction of C$_{60}$ mono-layer and Pd clusters gives rise to electronic charge transfer at the interface and facilitates the dissociation and uptake of hydrogen, which lead to hydrogen storage. The first-principles studies are carried out by self-consistent plane-wave method. The interaction between ions and electrons is described by projector-augmented wave (PAW) approach. In our calculations, the C$_{60}$ monolayer is doped by the Pd$_{n}$ atoms on $h$-BN with $n$ = 1-4 and 15, but it also forms a metal-C$_{60}$ nano-array with the Pd clusters. Charge transfer occurs at the interface, from the Pd atoms towards the C$_{60}$ monolayer. This electronic property strongly depends on the nature and number of metal atoms. A large amount of charge transfer between the Pd atoms and the C$_{60}$ monolayer indicates a strong interaction under the ionic effect, in contrast with the interaction of the C$_{60}$ monolayer and a metallic surface. The $h$-BN surface merely gains 0.1 electrons via C$_{60}$, proving that $h$-BN is an insulating material. We also find that Pd is a good catalyst for dissociation and storage of hydrogen on the C$_{60}$ molecules. Hydrogen is sufficiently dissociated in the presence of the Pd atoms/clusters, which assists in bonding of the individual H atoms to C$_{60}$. Dehydrogenation of C$_{60}$H$_{x}$ is also discussed in energetics. [Preview Abstract] |
Wednesday, March 12, 2008 3:42PM - 3:54PM |
S24.00007: Investigation of Trapping Positions for Beryllium Atom in C$_{60}$ Fullerene and Electron Densities at$^{ 7}$Be Nucleus. Lee Chow, Archana Dubey, H.P. Saha, Gary S. Collins, R.H. Scheicher, N.B. Maharjan, S.R. Badu, R.H. Pink, M.B. Huang, T.P. Das We are investigating, using first-principles Hartree-Fock Roothaan procedure, the trapping sites for $^{7}$Be atom in C$_{60}$ Fullerene, following broadly the same procedure as in earlier work by our group for trapping of muonium [1]. A number of possible sites, including the center of the C$_{60}$ and various positions near the fullerene surface both outside and inside C$_{60}$ are being studied including the effect of relaxation in the positions of neighboring C atoms. Electron densities at the $^{7}$Be nucleus will be presented for the sites where the binding energy is positive to attempt to understand the observed anomalous electron capture rate compared to other systems where trapped $^{7}$Be atom has been studied [2]. Results of our investigations for$^{ 7}$Be atom in graphite and graphene will also be presented for comparison with $^{7}$Be in C$_{60}$. Possible influence of many-body effects will be discussed. [1] O. Donzelli, T. Briere, T.P. Das, Sol St. Comm. \underline {90 }663(1994), Indian J. Phys. \underline {67 }(Special Issue) 35 (1993) [2] Ohtsuki et al, Phys. Rev. Lett. \underline {93},112501, (2004) [Preview Abstract] |
Wednesday, March 12, 2008 3:54PM - 4:06PM |
S24.00008: Transfer of a Single Carbon Fullerene at Small Nano-Gap Yoshifumi Oshima, Yoshihiko Kurui, Kunio Takayanagi A single carbon fullerene shows jump-to-contact behavior in conductance evolution when bringing an electrode close to it. Theoretically, the jump-to-contact behavior has been explained by deformation of the fullerene, but, it has not been proved experimentally. In this study, we investigated the geometry of the fullerene at the moment of jump-to-contact using transmission electron microscope -- scanning tunneling microscope system. A single carbon fullerene was synthesized in-situ [1]. We sometimes observed that the single carbon fullerene was transferred back and forth between both electrodes at the bias voltage of 0.6 V when the gap distance became almost 1nm which was still tunneling regime in conductance. Such a transfer was never observed when the bias voltage was lower than 0.1 V. Since the conductance showed the order of 10$^{-1}$ G0 in pulse at the moment of transfer, the fullerene was suggested to be expanded along the gap to have a contact with the opposite electrode. [1] M. Yoshida et al., Jpn. J. Appl. Phys. 46, L67 (2007). [Preview Abstract] |
Wednesday, March 12, 2008 4:06PM - 4:18PM |
S24.00009: Boron Fullerenes: An Electronic Structure Study Arta Sadrzadeh, Olga Pupysheva, Ihsan Boustani, Boris Yakobson Using \textit{ab initio }calculations, we study electronic structure and frequency modes of B$_{80}$, a member of boron fullerene family made from boron isomorphs of carbon fullerenes with additional atoms in the centers of hexagons. We also investigate geometrical and electronic structural properties of double-rings with various diameters, which are important as building blocks of boron nanotubes, and as the most stable clusters among the studied isomers with no more than 36 atoms. Double-rings also appear as building blocks of B$_{80}$. Furthermore, we investigate the possibility of further stabilizing some of fullerenes by depleting them. [Preview Abstract] |
Wednesday, March 12, 2008 4:18PM - 4:30PM |
S24.00010: Magic Number of a Spherical Ca Cluster on C$_{60}$ Sungjong Woo, Young-Kyun Kwon Since the discovery of fullerenes, there have been a lot of interest in investigating the metal-fullerene clusters. Mass spectrum on the metal(M) covering on a C$_{60}$ complex showed a peak at M$_{32}$C$_{60}$. This magic number was theoretically explained using the geometry based on the C-Ca binding. However, such theories could not clearly reveal why the peak at M$_{32}$C$_{60}$, especially for calcium clusters, is so prominent compared to smaller number of metal atoms. Using {\it ab initio} MD simulations, we have found that for Ca covering with less than 32 atoms, Ca atoms tend to be retracted to a cluster rather than to be bound on each face of C$_{60}$ even though the Ca atoms are deposited symmetrically. Such a cluster does not have specific number of atoms and it is bound to C$_{60}$ through van der Waals interaction. However, once Ca forms a spherical shell with 32 atoms, the structure is quite rigid so that it will not be retracted to a cluster. We have also found that the interaction between an individual Ca atom and each C$_{60}$ face gets loosen so that C$_{60}$ can rotate within Ca$_{32}$ sphere. The phonon spectrum has been obtained by spectral analysis and electronic orbitals of Ca$_{32}$C$_{60}$ will also be presented. [Preview Abstract] |
Wednesday, March 12, 2008 4:30PM - 4:42PM |
S24.00011: First principles study of cubane and alkali doped C60 solids Young-Moo Byun, Vincent Crespi Alkali doped fullerene (C60) solids have been studied widely due to their interesting physical properties. Lately, an experimental group succeeded to dope cubane (C8H8) into the octahedral voids of faced-centered-cubic (FCC) C60 solids, demonstrating that not only atoms (and polyatomic cations), but also small neutral molecules can intercalated into C60 solids. We study the electronic properties of cubane-doped C60 solids using first-principles techniques and show that C60 solids doped with both cubane and alkali metals, in which alkali metals such as K and Rb occupy the tetrahedral voids are energetically favorable. Cubane molecules substantially dilate the C60 lattice, resulting in a very large density of states in a single-particle treatment and pronounced tendency towards electronic instability. [Preview Abstract] |
Wednesday, March 12, 2008 4:42PM - 4:54PM |
S24.00012: First principles electronic structure calculation of interstitial P doped C$_{60}$ solid. Shizhong Yang, Guang-Lin Zhao, Diola Bagayoko C$_{60}$ solid has a very low thermo-conductivity that can be utilized to improve the \textit{figure-of-merit} of thermo-electric devices. The selection of suitable doping elements and doping concentrations in C$_{60}$ bulk semiconductors, for best performance in thermoelectric applications, is of great interest. In this work, we calculated the electronic structure of solid C$_{60}$, interstitially doped with P, at concentrations varying from 1:240 to 1:60. We employed a density functional potential and the plane wave method. Both local density approximation (LDA) and generalized gradient approximation (GGA) potentials were considered. The stability, the electron densities of states, dopant location, carrier type, volume change, and charge transfers of P doped C$_{60}$ were calculated and compared to those of B, N, and Co doped C$_{60}$ solids. In the 1:60 doping case, we found that P doped C$_{60}$ solid is an n-type semiconductor with the dopant energy levels in the band gap, close to the top of conduction band. This work was supported in part by the Department of the Navy, Office of Naval Research (ONR, Grant No. N00014-4-1-0587) and by the National Science Foundation (Award No. HRD0503362 ). [Preview Abstract] |
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