Purified carbon nanoparticles investigated with HREM and Raman spectroscopy

Previous studies of fullerene-related materials (nanotubes, onions, etc.) have been almost exclusively performed with electron microscopy methods due to the heterogeneous character of the deposits produced in the electric arc. We report Raman spectra of carbon nanotubes which have been purified following the procedure of Ebbesen et al. The purity of the sample has been confirmed by high-resolution electron microscopy. The Raman spectra of carbon nanotubes with an average diameter of 10-12 nm show very little disorder-induced scattering and no curvature-induced phonon softening, in contrast to unpurified material which contains a large number of carbon nanoparticles. These experimental findings are confirmed by lattice-dynamical calculations. Preliminary low-loss EELS measurements on nanotubes reveal significant differences for the graphite interband transition and collective valence-electron plasmon excitation, which are attributed to the cylindrical structure of the nanotubes.