Improvement of mechanical properties of amorphous carbon films deposited on polycarbonate plastics

Amorphous carbon films have been deposited on polycarbonate surfaces using laser ablation technique. The polycarbonate substrates were treated with oxygen plasma prior to film deposition. Mechanical properties of the films were examined as a function of plasma pretreatment time. Results showed that the mechanical behavior of the carbon film improved with pretreatment time. A one-hour pretreated sample exhibited no cracking, good adhesion, low stress and a hardness of 5 GPa which is 20 times higher than that of bare polycarbonate. Spectroscopic ellipsometry was used to characterize the film and interface properties in order to understand the effect of plasma on polycarbonate surface. Computer modeling of the ellipsometry data revealed that the improvement of mechanical behavior of the films is due to the modifications of the polycarbonate surfaces after the oxygen plasma treatment. Further correlation studies of surface modification by oxygen plasma was carried out by atomic force microscopy and stress measurement. Optical emission spectra from the plasma plume during laser ablation showed that the neutral and ionic carbon atoms were the dominant species. We believe their presence plays a major role in controlling the properties of our diamond-like carbon films.