Electronic transitions in single-walled carbon nanotubes: A resonance Raman study

Resonance excitation profiles of the high-frequency peaks in the Raman spectra of single-walled carbon nanotubes normalized to the scattering intensity of CaF₂ are presented. We find separate resonances of metallic and semiconducting tubes throughout the visible and the near-IR excitation range. The resonance shift of samples with different mean diameters confirm the inverse proportionality of the resonant transition energy to the tube diameter. Smaller diameter tubes are found to have sharper resonances than larger tubes due to a 1/d^2 dependence of the Raman cross section.