Electronic properties of barium-intercalated single-wall carbon nanotubes

The structural and electronic properties of barium-intercalated single-wall carbon nanotubes were investigated using high-resolution electron energy-loss spectroscopy in transmission. The intercalation is fully reversible and causes an expansion of the intertube distance in the nanotube bundles similar to that in a Cs-doped nanotube. The analysis of the core-level excitations shows that, in contrast to the alkali-metal intercalated nanotubes, there is hybridization between nanotube and barium states and the barium intercalation gives rise to a perturbation of the nanotube electronic states above the Fermi level. As a consequence of hybridization and charge transfer the formation of a free charge carrier plasmon is observed. In the case of the highest doping, the unscreened plasmon energy is about two times higher than that of the fully alkali-metal-doped nanotubes.