Electronic and structural properties of silicon-doped carbon nanotubes

Predictions of the electronic and structural properties of silicon substitutional doping in carbon nanotubes are presented using first-principles calculations based on the density-functional theory. A large outward displacement of the Si atom and its nearest-neighbor carbon atoms is observed. For the two tubes studied [metallic (6,6) and semiconducting ( 10,0)] the formation energies of the substitutional defects are obtained around 3.1 eV/atom. In the doped metallic nanotube case a resonant state appears about 0.7 eV above the Fermi level, whereas for the semiconductor tube, the silicon introduces an empty level at approximately 0.6 eV above the top of the valence band.