Intermediate frequency Raman spectra of defective single-walled carbon nanotubes

We simulated Raman spectra of defective single-walled carbon nanotubes within a non-orthogonal tight-binding model. The creation of defects in the nanotubes effectively lowers their symmetry and makes a large number of phonons Raman-active. The Raman spectra of such nanotubes will be similar in shape to their phonon density of states (PDOS). Assuming that for a low density of defects the change of the PDOS is negligible with respect to that of perfect nanotubes, we used the latter as an approximation of the former. The Raman scattering from perfect nanotubes is essentially resonant. Similarly to above, neglecting the change of the electronic structure due to a low density of defects, we adopted the same resonance conditions for defective nanotubes as for perfect ones. Based on these assumptions, we modeled the resonant Raman spectra of a sample of defective nanotubes by means of the PDOS of perfect nanotubes. The obtained results can be used for interpretation of experimental Raman spectra of defective nanotube samples.