Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session Y25: Fullerenes and Nanographite |
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Sponsoring Units: DCOMP DMP Chair: Tunna Baruah, Howard University Room: LACC 501A |
Friday, March 25, 2005 11:15AM - 11:27AM |
Y25.00001: Electronic transport, structure, and energetics of endohedral Gd@C82 metallofullerene and nanopeapods L. Senapati, J. Schrier, K. B. Whaley Electronic structure and transport properties of the fullerene C$_{82 }$and the metallofullerene Gd@C$_{82}$ are investigated with density functional theory and the Landauer-Buttiker formalism for transport. The metal binding site for Gd is found to differ from that in Sc, Y, and La metallofullerenes, and is located on the C$_{2}$ symmetry axis, adjacent to the C-C double bond. Insertion of Gd into C$_{82 }$causes a slight deformation of the carbon structure in the vicinity of the Gd atoms. Significant overlap of the electron distribution is found between Gd and the C$_{82}$ cage, with the transferred Gd electron density localized mainly on the nearest carbon atoms. This charge localization reduces some of the conducting channels for the transport, resulting in a reduction in the conductivity of the Gd@C$_{82}$ species relative to the empty C$_{82}$ molecule. The electron transport across the metallofullerene is found to be relatively insensitive to the spin of the transported electrons relative to that of the Gd atom. In addition, we present results of transport calculations when the optimized Gd@C$_{82 }$is inserted into a carbon nanotube to form a nanopeapod structure. [Preview Abstract] |
Friday, March 25, 2005 11:27AM - 11:39AM |
Y25.00002: Modification of electronic properties of nanographite due to chemical treatments Dmitriy Dikin, Sasha Stankovich, Xinqi Chen, Richard Piner, Rodney Ruoff, Oleksandr Chernyashevskyy, SonBinh Nguyen Electronic and magnetic properties of nanostructured graphite platelets and individual graphene sheets are highly anisotropic and exhibit high sensitivity to adsorption, doping and intercalation. The magnetization results obtained at room temperature for pristine graphite, graphite oxide, and chemically or thermally reduced graphite oxide show direct correlation between oxidation and reduction treatments. Diamagnetic response for graphite oxides is significantly decreased compared to the pristine material, and is restored back in chemically and thermally reduced samples, so the electronic properties can be modified in a controlled manner. At low temperatures all of the measured samples exhibit paramagnetic behaviour, which dominates for thermally treated graphite oxide. SEM and AFM are also used in our study to analyse the electronic and chemical modifications of nanographite. We gratefully acknowledge the \textit{NASA University Research, Engineering and Technology Institute on Bio Inspired Materials (BIMat)} under award No. NCC-1-02037. SEM was done at the Electron Probe Instrumentation Center at Northwestern University. [Preview Abstract] |
Friday, March 25, 2005 11:39AM - 11:51AM |
Y25.00003: Theoretical calculations on the mechanism of local polymerization and depolymerization of C$_{60}$ Shigeru Tsukamoto, Masato Nakaya, Tomonobu Nakayama, Masakazu Aono A reversible chemical reaction between C$_{60}$ molecules, polymerization/depolymerization, has been realized and controlled using an STM tip: the polymerization and depolymerization occur at negative and positive sample bias conditions, respectively. Using a first-principles calculation method, we investigated the mechanism responsible for the experimental results. The electronic structures were calculated for polymerized and depolymerized structures of C$_{60}$ dimers under negatively and positively ionized conditions as well as neutral condition. When a couple of C$_{60}$ is negatively ionized, the added electron occupies the initially unoccupied bonding orbital between C$_{60}$ molecules. Then the activation barrier of a polymerization is reduced. When a C$_{60}$ dimer is positively ionized, the bonding orbital energetically approaches to Fermi level and the activation barrier of depolymerization process is reduced. [Preview Abstract] |
Friday, March 25, 2005 11:51AM - 12:03PM |
Y25.00004: First principles investigation of one monolayer of C60 on h-BN/Ni(111) Jingguang Che, Hai-Ping Cheng The geometric and electronic structures of a monolayer of C60 on a monolayer h-BN on Ni(111) surface are studied by first principles calculations. The interaction between ions and electrons is described by the projector-argumented wave method. The most stable structure is found to be N on the top and B on the fcc site of Ni(111). The structure in which a hexagon of the C60 molecular is parallel to the substrate is 0.1eV in energy more favorable than that of a pentagon parallel to the substrate. For the most stable adsorption sites of C60 on h-BN/Ni (111), the distance between the bottom hexagon of C60 and the h- BN/Ni substrate is 3.6A. The calculated results show that the energy differences for different orientations are all smaller than 0.2eV. No magnetic moment is found for C60 monolayer. The calculated electronic structures confirm that the h-BN/Ni(111) may be a good insulator platform to study the electronic structures of C60 ultrathin films, since only a weak interaction and a few charge transfer exist between C60 and h-BN/Ni(111). [Preview Abstract] |
Friday, March 25, 2005 12:03PM - 12:15PM |
Y25.00005: The structural and electronic properties of a K-doped C60 monolayer of on h-BN/Ni(111) Hai-Ping Cheng, Jingguang Che The structural and electronic properties of a K-doped C60 monolayer are investigated using first principles calculations based on density functional theory. The K-doped C60 monolayer is deposited on an insulator h-BN monolayer on a Ni(111) surface. The interaction between ions and electrons is described by the projector-argumented wave method (PAW). It is found that K atoms are incorporated into the interstitial sites of the C60 monolayer with a distance of 2.9$\sim$3.0A to the h-BN/Ni substrate, while the distance of a hexagon face of C60 to the substrate is 3.6A. The calculated results indicate that with K doping the electron occupation on bands that are derived from the C60 lowest unoccupied molecular orbital (LUMO) is enhanced. For doping of four K atoms per C60 molecule, the LUMO is almost half- filled. Detailed analysis and comparison with an un-doped C60 monolayer on the same substrate and with pure metal surfaces will be presented. [Preview Abstract] |
Friday, March 25, 2005 12:15PM - 12:27PM |
Y25.00006: Theoretical Study of Stabilization of Fullerene-like Silicon Cages Ajit Hira, Nichole Moya-Leyba, Daniel Bulnes We extend our work on fullerenes$^{1}$, by exploring the stabilization of fullerene-like silicon cages through intercalation of carbon atoms. \textit{Ab initio} theoretical techniques are used to derive the physical and chemical properties of various (Si$_{60})_{m}$C$_{n }$systems (m = 1-3, n =1-10). The first phase of our investigation focuses on endohedral and exohedral complexes of a single Si$_{60 }$with$_{ }$C$_{n }$clusters. Electron correlation effects are incorporated using both Many Body Perturbation Theory (MBPT) and Density Functional Theories (DFT). The second phase of the investigation examines the interactions of the fullerene-like silicon "super molecules" with the small carbon clusters. The properties discussed will include bondlengths, ground-state energies, optimum absorbate distances, dissociation channels, and dissociation energies are presented. Possibilities exist for applications in silicon-based electronics at the nano scale. \begin{enumerate} \item A. S. Hira and A. K. Ray, Phys. Rev. \textbf{A 52}, 141(1995); \textbf{A 54}, 2205(1996). \end{enumerate} [Preview Abstract] |
Friday, March 25, 2005 12:27PM - 12:39PM |
Y25.00007: Theoretical Study of Na3-C60 and Na4-C60 Clusters: Pathways to Nanoscale Contacts Daniel Bulnes, Nichole Moya-Leyba, Erica Velarde, Ajit Hira We continue our interest in fullerene-alkali complexes$^{1-2}$ by investigating the physical and chemical properties of Na$_{3}$-C$_{60 }$and Na$_{4}$-C$_{60}$ systems. Five categories of adsorption sites for the alkali atoms on the fullerene molecule, namely fivefold, threefold, midbond-long, midbond-short and top, are considered. Electron correlation effects, using both Many Body Perturbation Theory (MBPT) and Density Functional Theories (DFT) are incorporated in the calculations for binding energies and optimal intermolecular bondlengths. For these complexes, various properties including bondlengths, ground-state energies, optimum absorbate distances, dissociation channels, and dissociation energies are presented. Possibility of tunneling between different sites is investigated. We also examine implications for the fabrication of nanoscale contacts, and for the study of dynamical systems involving C$_{60}$. \begin{enumerate} \item A. S. Hira and A. K. Ray, Phys. Rev. \textbf{A 52}, 141(1995); \textbf{A 54}, 2205(1996). \item A. S. Hira, Billy Terrazas, Erica Velarde and Desirae Vigil, ``An \textit{Ab Initio} Theoretical Study of Alkali-C$_{60}$ and Alkali-(C$_{60})_{n}$ Clusters,'' Bull. Am. Phys. Soc. \textbf{49}, 599 (March 2004). \end{enumerate} [Preview Abstract] |
Friday, March 25, 2005 12:39PM - 12:51PM |
Y25.00008: Hyperfine coupling of endohedral fullerene Sc@C82 Seung Mi Lee, B.J. Herbert, J.C. Green, D. Nguyen-Manh, A. Ardavan, J. van Tol, A.P. Horsfield, G.W. Morley, K. Porfyrakis, D.G. Pettifor, G.A.D. Briggs The hyperfine coupling of the endohedral metallofullerene, Sc@C$_{82}$, which is a candidate qubit for quantum computing, has been investigated theoretically and experimentally. Using density functional theory (DFT), we have systematically studied the molecular structures and energetics of nine isomers of C$_{82 }$and Sc@C$_{82}$ fullerenes. DFT predicts that the most stable isomer has $C_{2v}$ symmetry with the Sc atom lying off-centre along the $C_{2 }$ symmetry axis and forming partially covalent bonds with a carbon hexagonal ring of the fullerene cage. The hyperfine couplings between the unpaired electron spin and the Sc and C atoms have been calculated and compared to the electron spin resonance (ESR) spectra. The experimental isotropic hyperfine coupling constants confirm the $C_{2v}$ symmetry predicted for the ground state isomer. Furthermore, the calculated anisotropy of the hyperfine coupling tensor is in good agreement with low temperature experimental measurements. www.nanotech.org [Preview Abstract] |
Friday, March 25, 2005 12:51PM - 1:03PM |
Y25.00009: Evidence of nanosegregation and Jahn-Teller effect in Na$_2$C$_{60}$ Katalin Kamar\'as, Gy\"ongyi Klupp, P\'eter Matus, L\'aszlo F. Kiss, S\'andor Pekker, Dario Quintavalle, Andr\'as J\'anossy, Norbert M. Nemes, Craig M. Brown, Juscelino Leao Na$_2$C$_{60}$ is the only known solid fulleride salt containing the divalent fulleride ion C$_{60}^{2-}$. Calculations predict a Jahn-Teller distortion of this ion, similar to the A$_4$C$_{60}$ compounds, to which they are related by electron-hole symmetry. However, by combining various experimental methods, we found that divalent ions exist only above 450 K in solids with composition Na$_2$C$_{60}$; at room temperature and below, methods sensitive to molecular symmetry and charge (infrared absorption, ESR, NMR) detect at least two phases, most probably C$_{60}$ and Na$_3$C$_{60}$. We explain our data by a model where nanosegregated regions of the size 3-30 nm with different Na concentration coexist. The concentration gradient disappears at higher temperature by diffusion of sodium, observed by neutron scattering. High temperature infrared spectra show evidence of a uniaxial (D$_{3d}$/D$_{5d}$) distortion of the fullerene balls. [Preview Abstract] |
Friday, March 25, 2005 1:03PM - 1:15PM |
Y25.00010: Fermi surfaces of pure and K-doped C$_{60}$ monolayer on Cu(111) surfaces studied by high resolution angle-resolved photoemission spectroscopy K.-D. Tsuei, C.-M. Cheng, C.-C. Wang, J.-Y. Yuh The electronic structure of C$_{60}$ on Cu(111) surfaces has been studied by high-resolution photoemission. The LEED pattern for one monolayer C$_{60}$ on a Cu(111) surface shows a sharp (4x4) pattern. In photoemission the LUMO-derived band is a partially filled by charge transfer from Cu surface and the spectrum is similar to that of gas phase C$_{60}^{-}$. The satellite peaks of LUMO indicate strong electron-phonon coupling. Comparing to spectra of K doped films the undoped 1 ML film was found to have nearly half-filled LUMO or ``K$_{3}$C$_{60}$,'' in contrast to 0.8e found in a recent calculation. [1] The Fermi surface was mapped by angle-resolved photoemission. It shows a clear electron-like pocket near the zone center, unlike the hole-like Fermi surface in ``K$_{3}$C$_{60}$'' on Ag(111), [2] due to different C$_{60}$ orientation. In the case of Cu the Fermi surface near the zone center accounts for only 0.1 electrons. Near the K-point at least one hole-like Fermi surface can be observed. The detailed Fermi surface will be discussed. [1] L.-L. Wang and H.-P. Cheng, Phys. Rev. B 69, 045404 (2004). [2] W. L. Yang et al., Science 300, 303 (2003). [Preview Abstract] |
Friday, March 25, 2005 1:15PM - 1:27PM |
Y25.00011: Understanding the Dynamics of Kr@C$_{60}$ : A Far-Infrared Vibrational Study S. Brown, J. Cao, J.L. Musfeldt, N. Dragoe, A. Revcolevski, Y. Yokoyama, S. Ito, A. Takeda, T. Miyazaki, H. Takagi, H. Shimotani, F. Cimpoesu, K. Kitazawa The C$_{60}$ molecule has remarkable ability to encapsulate atoms inside the hollow carbon cage. Here, we report a high-resolution far infrared spectral investigation of endohedral Kr@C$_{60}$. Unexpected softening of the T$_{1u}$(1) mode ($\sim$528 cm$^{-1}$) and sharp peak at $\sim$600 cm$^{-1}$ have been observed throughout the temperature range of investigation. The response of Kr@C$_{60}$ is compared to that of pristine C$_{60} $, and the spectral differences are discussed in terms of local symmetry and prospects of Kr@C$_{60}$ as a building block for organic superconductors. [Preview Abstract] |
Friday, March 25, 2005 1:27PM - 1:39PM |
Y25.00012: Negative Differential Resistance and Current Rectification in C$_{60}$ Multilayers Michael Grobis, Andre Wachowiak, Ryan Yamachika, Michael Crommie Electronic components exhibiting negative differential resistance (NDR) and current rectification (CR) play a crucial role in modern electronic devices. Though most such devices are based on semiconducting technology, several molecular systems have been recently shown to exhibit NDR and CR that involve very different mechanisms. This talk will focus on NDR and CR behavior seen in our scanning tunneling spectroscopy studies of C$_{60}$ multilayers on metal surfaces. The NDR mechanism observed here appears to differ from those seen in previous studies and is consistent with the behavior expected from a bias-dependent tunneling barrier height. [Preview Abstract] |
Friday, March 25, 2005 1:39PM - 1:51PM |
Y25.00013: Doping dependence of C$_{60}$ monolayers studied by scanning tunneling microscopy Ryan Yamachika, Andre Wachowiak, Michael Grobis, Michael Crommie The electronic properties of C$_{60}$ compounds can be tuned by charge-doping them with alkali impurities. This results in an interplay between molecular charge transfer, Coulomb repulsion, phonon coupling, and nearest neighbor interactions. Here we present a scanning tunneling microscopy/spectroscopy study of K doped C$_{60}$ monolayers on Au(111). We find that the morphology and electronic structure of C$_{60}$ monolayers change significantly with doping level. In addition to LUMO/LUMO+1 shifts, we observe strong variations in the low-energy local density of states. [Preview Abstract] |
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