Spectroscopic analysis of different types of single-wall carbon nanotubes

– The Raman response of the radial breathing mode in single-wall carbon nanotubes was analyzed for excitation with 10 different laser lines. The line shape was fitted with 14 Voigtian oscillators which could be correlated to tubes of different helicity. The strongest lines were observed between 172 and 199 cm. For an assignment frequencies evaluated from a density functional calculation and scattering intensities for the resonance transitions were used. The 5 strongest lines observed are consistent with scattering from tubes with 11 different helicities. From the evaluation of the scattering intensities the nearest-neighbor integral between two carbon atoms on the curved sheet was found to be 2.6± 0.5 eV. Since the discovery of carbon nanotubes this material attracts increasing interest in the community of scientists studying nanomaterials. However, the fundamental properties of the individual tubes could not be investigated until a technology was provided to prepare large amounts of single-wall nanotubes (SWNTs). This possibility was first demonstrated by Thess et al. [1] using laser evaporation of a graphite target doped with 2% Ni/Co catalyst. The resulting tubes were found to have a rather uniform diameter and to condense into bundles or ropes with a triangular structure. From the X-ray analysis the length of the unit cell for this structure is 1.7 nm, corresponding to a diameter of 1.38 nm for the individual tubes. At this point the quantitative descriptions of the structure and electronic properties of cylindrical graphene sheets became important as they were developed a few years before [2,3]. The single-wall tubes consist of a graphene sheet rolled up along an arbitrary lattice vector with components (n,m). Tubes with n = m are labeled armchair, tubes with either n = 0 or m = 0 are labeled zigzag. All other tubes are chiral. The observed diameter of 1.38 nm is consistent with (10, 10) and (17, 0) tubes. The rolled-up graphene sheet represents an exactly one-dimensional lattice with the fun-