INVESTIGATION OF THE ELECTONIC STATES OF SINGE-WAL CARBON NANOTUBES PROBED BY RESONANCE RAMAN SCATTERING

我们有方法光学滥用spectra and resonance Raman spectra for various kinds ofsinglewall carbon nanotubes (SWNTs) with different diameter distributions fabricated by thelaser-furnace and carbon arc methods using NiCo, Ni, RhPd, RhPt，NiY catalysts. We developed a "splay method" to make SWNT thin film and measured the opticalabsorption.我们发现三个absorption bands from near infrared to visible which are flecting π ->π - 1 transitions between spike-like density of states originating from the one-dimensional vanHove singularities. The absorption structures with changing The diameter of The SWNT. Itwas found the first and the second absorption peaks correspond to the optical transitionssemiconductors and the third one the metallic SWNTs. Raman spectrum taken with the laser excitationat the absorption band of metallic SWNTs shows a Fano line shape which is characteristics ofmetallic materials. Thus，我们命名third absorption band as "metallic window".Most of synthesis methods provide “bundles”of SWNTs. Thus，这是非常重要的，以投资bundle的效果，它是expected that the doped brominemolecules can be removed by the evacuation if the molecules located around isolated SWNTs whilemolecules inside SWNTs bundles cannot be removed. Using this doping-dedoping technique，我们已经有了明确的关联Raman scattering of isolated SWNTs.我们发现了isolated metallicSWNTs do not show Fano line shape anymore. This indicates clearly that the Fano interference isintrinsic to the metallic SWNT "bundles". Further，我们发现高已获得的SWNTs samples show very thick bundle structures.我们已经掌握了resonance Raman scattering of the purified samples and found that the radial breathing modes showlarge up-shifts which is predicted by theoretical calculation about Van der Waals interactionsbetween swnts。

We have measured optical absorption spectra and resonance Raman spectra for various kinds of single-wall carbon nanotubes (SWNTs) with different diameter distributions fabricated by the laser-furnace and carbon arc methods using NiCo, Ni, RhPd, RhPt, NiY catalysts. We developed a "splay method" to make SWNT thin film and measured the optical absorption. We found three absorption bands from near infrared to visible which are reflecting π -> πィイD1*ィエD1 transitions between spike-like density of states originating from the one-dimensional van Hove singularities. The absorption structures changes with changing the diameter of the SWNT. It was found that the first and the second absorption peaks correspond to the optical transitions of semiconductors and the third one the metallic SWNTs. Raman spectrum taken with the laser excitation at the absorption band of metallic SWNTs shows a Fano line shape which is characteristics of metallic materials. Thus, we named the third absorption band as "metallic window".Most of synthesis methods provide "bundles" of SWNTs. Thus, it is very important to investigate the effect of the bundle. It is expected that the doped bromine molecules can be removed by the evacuation if the molecules located around isolated SWNTs while the molecules inside SWNTs bundles cannot be removed. Using this doping-dedoping technique, we have measured resonance Raman scattering of isolated SWNTs. We found that the isolated metallic SWNTs do not show Fano line shape anymore. This indicates clearly that the Fano interference is intrinsic to the metallic SWNT "bundles". Further, we found that highly purified SWNTs samples show very thick bundle structures. We have measured the resonance Raman scattering of the purified samples and found that the radial breathing modes show large up-shifts which is predicted by theoretical calculation about Van der Waals interactions between SWNTs.