Second-order resonant Raman spectra of single-walled carbon nanotubes

An analysis of the second-order resonant Raman spectra of single-walled carbon nanotubes using different laser energies in the range 1.58–2.71 eV is presented. Major emphasis is given to the overtones and combination modes associated with the two dominant features of the first-order spectra, the radial breathing mode and the tangential mode. Both of these modes, as well as their second-order counterparts, are associated with resonant enhancement phenomena arising from electron-phonon coupling to the unique one-dimensional density of electronic states for the single-wall carbon nanotubes.