Band filling and correlation effects in alkali metal doped carbon nanotubes

We have investigated modification of the electronic structure of the vertically aligned multi-walled carbon nanotubes (MWCNTs) as a function of sodium doping. The changes in band structure can be largely associated with shifts of the Fermi level position relative to the multi-walled carbon nanotube band structure. The changes in the apparent density of states in the vicinity of the Fermi level suggest effects associated with the repulsive on-site Coulomb interaction (the correlation energy) although the intrinsic poor screening in the quasi-one-dimensional carbon nanotubes, particularly near the tube termination, cannot be neglected entirely, The results are compared with 'unaligned' single-walled and multi-walled carbon nanotube films (or mats).