RAMAN-SCATTERING OF LIGHT AND IR ABSORPTION IN CARBON NANOTUBES

Raman light scattering and IR absorption spectra of samples containing multilayer carbon nanotubes in different stages of purification by th e selective oxidation technique have been investigated. It was found t hat the Raman spectra of carbon nanotubes exhibit softening of the mod e at 1582 cm(-1) corresponding to E-2g vibrations of graphite hexagons and a line at 120 cm(-1) due to the radial vibrations of nanotubes. I n IR absorption spectra measured in the region of 0.07-0.3 eV, several sets of lines with a spacing of 15 meV (120 cm(-1)) between lines of each group have been detected. We suggest that each group corresponds to electron transitions generating electron-hole pairs in semiconducti ng nanotubes and contains a phononless 00-line and its phonon replicas with spacing between them equal to the ''breathing'' mode energy of 1 20 cm(-1). Measurements of electric conductivity at a frequency of 930 0 MHz indicate that, in addition to semiconducting nanotubes, the samp les contain nanotubes with properties of a highly disordered semimetal . (C) 1998 American Institute of Physics. [S1063-7761(98)02305-1].