Optical absorption from graphitic clusters of hydrogenated amorphous carbon thin films

The optical absorption of hydrogenated amorphous carbon films (a-C:H) was measured by spectroscopic ellipsometry. The a-C:H films were deposited at different substrate temperatures by rf-plasma of methane. A volume distribution of graphitic cluster size was assumed to reproduce the experimental spectra of the absorption coefficient. The changes in the absorption coefficient and the optical gap, induced by deposition temperature, have been interpreted in terms of changes in the graphitic cluster size of the network. The increase in the deposition temperature produces an increase in the size of the graphitic clusters.