Resonant Raman Scattering in Carbon Nanotubes

Abstract

We present resonant-Raman scattering results on single and multi-walled carbon nanotubes in the range 1.5 to 2.6 eV. In addition to the known resonance of metallic tubes with a maximum at ≈︂1.9 eV we determine the resonance profile of semiconducting single-walled tubes. For a diameter of d0 = 1.3 nm it has a flat minimum between 1.8 and 2.3 eV and a resonance above and below that. For tubes with d_0 = 1.45 Å all resonance energies decrease by about 0.1 eV. For multi-walled tubes a monotonic increase in Raman intensity with excitation energy is observed which is explained as a smearing out of the square-root singularities in the electronic density of states of 1D systems.