The influence of the magnetron sputtering deposition parameters on optical properties of a-C:H thin films

Tetrahedral, highly hydrogenated amorphous carbon films were deposited using rf sputtering of graphite by a magnetron sputter source in Ar/CH4 atmosphere. The optical band gap, Urbach energy and refractive index of the deposited films were studied as a function of the bias voltage applied to the substrate during deposition and gas pressure. The films were characterized by visible spectroscopy, The variation of the optical band gap is considered as the result of the transition from unsaturated graphitic sp(2) bonds to tetrahedral diamond-like sp(3) bonds in the film. The variation of the refractive index is correlated with the density and optical band gap of the films.