Low-frequency Raman modes in Cs- and Rb-doped single wall carbon nanotubes

Single wall carbon nanotubes (SWNT) doped at saturation by alkali-metals ar e investigated by Raman scattering The Raman profiles in the frequency rang e of the tangential modes (TM) are close for Cs and Rb doping and only weak ly dependent on the laser energy. This loss of resonance is assigned to a l oss of Van Hove singularities in the electronic density of states. The most striking intrinsic features of the doped compounds are two low-frequency p eaks assigned to modes involving both radial motions of tubes and alkali-at oms vibrations. (C) 2001 Elsevier Science B.V. All rights reserved.