Resonance Raman scattering and diameter-dependent electronic states in single-wall carbon nanotubes

Resonance Raman scattering has been measured with laser wavelengths of 450-800 nm on single-wall carbon nanotubes with diameters of 1.1-1.4 nm. The observed intensity enhancements of the Raman peaks reveal resonance electronic transitions at 700, 750 and 780 nm for nanotubes with energies of the breathing mode at 184, 171 and 162 cm^-1, respectively. Calculations show that these nanotubes have diameters of 1.21, 1.29 and 1.37 nm, respectively, and exhibit metallic electronic structures produced by the zone-folding effect. It is shown that metallic and semiconducting nanotubes can be distinguished by Raman scattering.