Dispersive Raman spectra observed in graphite and single wall carbon nanotubes

The disorder-induced D-band and some other non-zone center Raman modes of graphite and single wall carbon nanotubes are assigned to phonon modes in their respective Brillouin zones. In disordered graphite, the weak, dispersive phonon modes, which have been known but never assigned so far, are well described by the double resonance Raman process. All weak Raman peaks observed for sp2 carbons are useful for determining the phonon dispersion relations of graphite. In carbon nanotubes, all semiconducting nanotubes and some metallic nanotubes have van Hove singular k points for their electronic and phonon energy dispersion curves at the Γ point of the Brillouin zone. A corresponding Raman process is relevant to explain the observed D-band and intermediate frequency spectra.