High-resolution electron microscopy and inelastic light scattering of purified multishelled carbon nanotubes

Raman spectra of purified carbon deposits containing multishelled carbon nanotubes of average diameter 10–12 nm show narrow vibrational bands and no phonon softening in contrast to unpurified material. This is in agreement with lattice-dynamical calculations using a semiempirical pseudopotential, which predicts no significant phonon softening in this size range. Only a very weak disorder-induced vibrational band at 1356 ${\mathrm{cm}}^{\mathrm{-}1}$ (${\mathit{I}}_{\mathit{G}}$/${\mathit{I}}_{\mathit{D}}$=0.04) is found for the unpurified as well as purified carbon deposits, which suggests that the scattering is originated by structural defects rather than by size effects.