Raman spectroscopy of HiPCO single-walled carbon nanotubes at 300 and 5 K

Single-walled carbon nanotubes (SWNTs) produced by the high pressure CO disproportionation (HiPCO method) and purified by controlled thermal oxidation in air have been studied by Raman spectroscopy at 300 and 5 K. Raman spectra have been observed at lambda(exc)=632.8 and 441.6 nm laser excitation in the range of 160-1800 cm(-1). In the low-frequency part of the spectra (the radial breathing mode range) eleven narrow lines can be detected at low temperatures, enabling an estimation of nanotube diameters (0.8-1.3 nm) and chirality. The width at half-maximum intensity of these spectral lines is about 3-4 cm(-1) at 5 K. The Stokes and anti-Stokes spectra are measured at lambda(exc) =632.8 nm at room temperature. The most intense lines in these spectra are caused with the resonant Raman-scattering process. With increasing temperature from 5 to 300 K the shift (3-4 cm(-1)) of the most intense high-frequency component of the tangential mode (G mode) to lower frequency is observed. Based on the analysis of the Stokes/anti-Stokes spectra and the G band shape, the corresponding lines were identified with metallic or semiconducting type of nanotubes. (C) 2003 Published by Elsevier Science Ltd.