DLC-SiOx nanocomposite films deposited from CH4 : SiH4 : O2 gas mixtures

Nanocomposite DLC-SiOx films were deposited by PECVD from CH4: SiH4:O2 gas mixtures. The effects of gas mixture composition and self-bias voltage on the optical and mechanical properties of these films were investigated. Results show that high optical gap (~3 eV) coatings can be obtained at low oxygen contents in the gas mixture (~5 vol.%). At low self-bias voltages, oxygen incorporation increases the deposition rate of the films. On the other hand, at bias voltages larger than 200 V oxygen incorporation decreases the deposition rate revealing that etching of the films is dominant. Nevertheless, oxygen is incorporated into the films mainly as SiOx, competing with the formation of the DLC phase. Residual internal stress of the films are reduced to about 1 GPa, while hardness is approximately constant in the range from 13 to 14 GPa. All investigated DLC-SiOx nanocomposite films turned out to be more hydrophilic than pure DLC as determined by contact angle measurements.