Investigation of hydrocarbon-plasma-generated carbon films by electron-energy-loss spectroscopy

Abstract

The bonding in hard, hydrogenated, amorphous carbon films ($a$-C:H) prepared by plasma decomposition of benzene was investigated by high-resolution electron-energy-loss spectroscopy. In all asgrown films we find that one-third of the carbon atoms are trigonally bonded and two-thirds of the carbon atoms are tetrahedrally bonded. For the trigonally bonded part, the dielectric properties reveal a transformation from polymeric state for samples prepared with low ion energy to a more graphitic state for films prepared with higher ion energy. Upon annealing, the number of carbon atoms in ${\mathrm{sp}}^{2}$ configuration increases. The graphitization of the films is observed in two steps at 200\ifmmode^\circ\else\textdegree\fi{}C and at 400\ifmmode^\circ\else\textdegree\fi{}C. A closing of the optical gap and a delocalization of the $\ensuremath{\pi}$ electrons is observed between 400\ifmmode^\circ\else\textdegree\fi{}C and 600\ifmmode^\circ\else\textdegree\fi{}C.