Electronic properties of clean and Li-doped single-walled carbon nanotubes

We have investigated the electronic properties of clean and Li-doped single-walled carbon nanotubes (SWCNTs) using several spectroscopic techniques. For the clean sample the overall shape of the valence band photoemission and X-ray absorption spectra show the characteristic features of C atoms in sp2 hybridization, as in graphite. C 1s photoemission spectrum shows instead a broader peak, with a full width at half maximum of 0.43 ± 0.02 eV. Close to the Fermi level and at low loss energy, peaks due to van Hove singularities have been observed in the photoemission and electron energy loss spectra of SWCNT mats, respectively. At 150 K, the Li doping saturates at a Li/C concentration of about 0.06, causing a shift of the photoemission peaks towards higher binding energy by about 0.25 eV, and an increase in the spectral intensity near the Fermi level. This result is consistent with an electron charge transfer from Li atoms and the partial filling of the SWCNT conduction band.