Stoichiometry dependence of the Raman spectrum of alkali-doped single-wall carbon nanotubes

Li-doped films with controlled stoichiometries were prepared by performing redox reactions between single-wall carbon nanotubes thin films and solutions of organic radical anions. A monotonic upshift of the tangential modes is evidenced for ${\mathrm{Li}}_x\mathrm{C}$ compounds $(0\mathrm{}<~x<~0.17).$ A similar doping dependence of the Raman profile is observed for vapor-phase Rb-doped samples. This universal behavior of the doping-induced upshift of the tangential modes is concomitant to a loss of absorption bands in the optical spectra and to a monotonic increase of the conductivity.