Local electronic properties of nanotubes:: heterojunctions and doped multiwall tubes

Electronic properties of carbon nanotube heterostructures are studied by investigating the behavior of the local density of states (LDOS) along the tubes. We determine how these properties change from the metallic to the semiconducting side of a nanojunction. We show that Friedel-like oscillations may not always be evident on the metallic side, and found clear exponential decays of the LDOS on the semiconducting side. Both behaviours are explained using a simple picture that relates the LDOS to the bulk electronic structure of the constituent parts of the system, being independent of the specific junction. Local electronic structure of metallic nanotubes have been also investigated as a function of the nanotube radius. We find that the LDOS exhibit well defined oscillations which may be directly predicted from size quantization effects. Calculations of total energy changes are performed in impurity-doped-multiwalled nanotubes and the results are shown to be determined essentially by the same electronic properties as those of the constituent tubes.