Electronic properties of tetrahedral amorphous carbon (ta-C) films containing nanotube regions

The electronic and optical properties of nitrogen doped tetrahedral amorphous carbon (ta-C:N) are compared with those of a new form of carbon ta-C film in which nanotube regions are included (ta-C:(NT)). It is found that nanotubes in ta-C inhibit the N doping effect in ta-C and leads to a reduction in conductivity. The results point to the nanotube regions acting as electronically isolated graphitic regions in ta-C. The refractive index in ta-C:(NT) is found to have the opposite dependency on wavelength to that of ta-C. It is proposed that the refractive index can be used as a signature for the presence of nanotubes and other large graphitic regions in ta-C.