RESONANT RAMAN EFFECT IN SINGLE-WALL CARBON NANOTUBES

A resonant Raman study of single-wall carbon nanotubes (SWNT) using se veral laser lines between 0.94 and 3.05 eV is presented. A detailed li neshape analysis shows that the bands associated with the nanotube rad ial breathing mode are composed of a sum of individual peaks whose rel ative intensities depend strongly on the laser energy, in agreement wi th prior work. On the other hand, the shape of the Raman bands associa ted with the tangential C-C stretching motions in the 1500-1600 cm(-1) range does not depend significantly on the laser energy for laser exc itation energies in the ranges 0.94-1.59 eV and 2.41-3.05 eV. However, new C-C stretching modes are observed in the spectra collected using laser excitations with energies close to 1.9 eV. The new results are d iscussed in terms of the difference between the 1D electronic density of states for the semiconducting and metallic carbon nanotubes.