Spectroscopic analysis of high order optical transition in semiconducting and metallic carbon nanotubes

We have studied line shape analysis of the Rayleigh scattering spectra of high order transition in structure assigned single wall nanotubes. For both semiconducting single wall nanotubes and metallic single wall nanotibe, we found that the main Rayleigh lines fit very well to an excitonic model, while a free carrier model failed to reproduce the spectroscopic features. We have presented on the systematic observations of phonon sidebands in the Rayleigh spectra of S33 and S44 transitions in semiconducting species. These features have been predicted to arise from exciton-phonon bound states. Such sidebands are not present near the M22 Rayleigh feature in metallic species. This is consistent with the reduced strength of excitonic interactions in metallic nanotubes. These finding provided direct evidence for an excitonic description of higher order optical transitions in single wall nanotubes Rayleigh spectra of invidual suspended nanotubes were obtained using a commercial supercontinuum laser system. The raw spectra were corrected for the super continuum spectrum and for the systematic dependence of the scattering cross section for an infinite cylinder.