Optical properties of amorphous carbon films deposited by magnetron sputtering of graphite

The thermal stability of amorphous carbon (a-C and a-C:H) has been studied by ellipsometry and spectrophotometry in the visible and near-UV range (1.5–5.6 eV). The dielectric function of amorphous carbon has been derived and analyzed using the Kramers-Kronig technique. The conventional analytical approach is shown to be insufficient for the analysis of thermally treated samples. The fundamental absorption edge is analyzed with respect to collective effects in nanoscale fragments of the graphite-like component of the amorphous carbon structure. Two types of graphite-like clusters contributing to the spectral dependence of the fundamental absorption edge and modified by thermal treatment are revealed.