Influence of packing on the vibrational properties of infinite and finite bundles of carbon nanotubes - art. no. 205403

The quantitative analysis of the vibrational properties of carbon nanotubes is a key issue for the interpretation of Raman experiments. In particular. a reliable characterization of the atomic structure of single-wall carbon nanotubes produced under various conditions is mainly based on the interpre tation of low-frequency (100-300 cm(-1)) Raman spectra. In the present work . we analyze the influence of the packing of the tubes on these low-frequen cy modes. We find that the low-frequency spectra of crystals of single-wall carbon nanotubes present two intense Raman modes instead of a single fully symmetric A(1g). mode characteristic of isolated tubes. The second mode ha s a non-negligible intensity for crystals formed with nanotubes of radii la rger than 7 Angstrom. For finite number of tubes in a bundle, two breathing like intense modes appear as a specific signature. Finally, our simulation for inhomogenous bundles made of a large number of tubes does not reveal an y specific signature of the individual tubes in the low-frequency Raman spe ctra.