ARTICLES Rayleigh and Raman Scattering from Individual Carbon Nanotube Bundles

Rayleigh scattering spectra and Raman spectra from single bundles of aligned single-wall carbon nanotubes (SWNTs) have been obtained with dark field optical microscopy and Raman microscopy. Rayleigh scattering spectrum reveals resonance peaks due to the optically allowed interband transitions in SWNTs. The intensity of the resonance peaks was found to depend strongly on the incident light polarization. These resonance peaks are completely suppressed when the incident light polarization is perpendicular to the nanotube axis, suggesting that the interband transition dipole in SWNTs is orientated parallel to the tube axis. Polarized Raman measurements on aligned nanotubes in a single bundle show that the Raman scattering is polarized along the nanotube axis direction, and Raman scattering signal is strongest when the incident laser is polarized parallel to the tube axis. All strong Raman active modes behave as A1g. Tangential carbon stretching mode Raman scattering from semiconducting tubes shows very little change from bundle to bundle, while that from metallic SWNTs exhibits large variations. The broadened metallic Raman scattering at 1550 cm-1 can be well fitted by a Fano line shape function. This broadened Raman scattering depends sensitively on sample processing conditions. Charge transfer due to chemical doping is proposed to explain the change in Raman scattering from oxidized metallic tubes.