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 |     _________________________________________________________________
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 |   "The atomic structure of single wall carbon nanotubes probed by STM"
 |   
 |   A. Hassanien1, M. Tokumoto1, Y. Kumazawa2, H. Kataura2, Y. Maniwa2, 
 |   S. Suzuki2, and Y. Achiba2
 |   
 |   1Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki
 |   305-8568, Japan
 |   2Tokyo Metropolitan University, Minami-osawa, Hachi-oji, Tokyo
 |   192-0397, Japan
 |   
 |   [Abstract]
 |   A detailed three dimension structural analysis of single walled carbon
 |   nanotubes (SWNT) are studied by scanning tunneling microscopy operated
 |   at room temperature in ambient conditions. On a microscopic scale the
 |   images show that the tubes are condensed in ropes as well as separated
 |   with nearly uniform diameter ranges between 1.2 to 1.7 nm. For a
 |   single wall nanotube rope, the outer portion shows highly oriented
 |   nanotubes with no difference in their chirailty. On a separated
 |   nanotubes, atomically resolved images show variable chairality ranges
 |   between 7-27 degrees with no one type dominates. From STM and STS
 |   measurements we could confirm the correlation between chirality and
 |   the electronic properties, namely the tuning from metallic to
 |   semiconducting. We also observed a rectifying behavior correlated with
 |   chiral angle - an important observation for nano-devices application.
 |   
 |     _________________________________________________________________
 |                                      
 |   
 |   "Photophysical properties in C60 and higher fullerenes"
 |   
 |   Kikuo Harigaya
 |   
 |   [Abstract]
 |   The optical excitations in C60 and higher fullerenes, including
 |   isomers of C76, C78, and C84, are theoretically investigated. We use a
 |   tight binding model with long-range Coulomb interactions, treated by
 |   the Hartree-Fock and configuration-interaction methods. We find that
 |   the optical excitations in the energy region smaller than about 4 eV
 |   have most of their amplitudes at the pentagons. The oscillator
 |   strengths of projected absorption almost accord with those of the
 |   total absorption. Next, off-resonant third order susceptibilities are
 |   investigated. We find that third order susceptibilities of higher
 |   fullerenes are a few times larger than those of C60. The magnitude of
 |   nonlinearity increases as the optical gap decreases in higher
 |   fullerenes. The nonlinearity is nearly proportional to the fourth
 |   power of the carbon number when the onsite Coulomb repulsion is 2t or
 |   4t, t being the nearest neighbor hopping integral. This result,
 |   indicating important roles of Coulomb interactions, agrees with
 |   quantum chemical calculations of higher fullerenes.
 |   
 |     _________________________________________________________________
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 |   
 |   [$@Ld$$9g$o$;@h(J]
 |   $@FAK\T$(J TEL: 0298-54-5437 E-mail: madoka@etl.go.jp

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