Physical Review B 64, 205403 - 10 (2001)

Influence of packing on the vibrational properties of infinite and finite bundles of carbon nanotubes

L. Henrard, V.N. Popov, A. Rubio

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 interpretation 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-frequency 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 has a non-negligible intensity for crystals formed with nanotubes of radii larger than 7 Å. For finite number of tubes in a bundle, two breathinglike intense modes appear as a specific signature. Finally, our simulation for inhomogenous bundles made of a large number of tubes does not reveal any specific signature of the individual tubes in the low-frequency Raman spectra.

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http://dx.doi.org/10.1103/PhysRevB.64.205403