Deposition of amorphous hydrogenated carbon films on steel surfaces through the enhanced asymmetrical modified bipolar pulsed-DC PECVD method

Abstract

Deposition of amorphous hydrogenated carbon (a-C:H) films employing an asymmetrical bipolar pulsed-DC plasma enhanced chemical vapor deposition (PECVD) system, an active screen that worked as an additional cathode represented a step forward for thin film growth by using lower pressure and higher plasma density than the conventional PECVD system. Acetylene gas was used as a precursor. In order to overcome the low adherence of the a-C:H films on steel substrates, an amorphous silicon interlayer was deposited as an interface between the substrate and the films, using silane as a precursor. The films were analyzed according to their microstructural, mechanical, and tribological properties as a function of the substrate bias voltage. The film's atomic arrangements and the hydrogen content of the films were estimated by means of Raman spectroscopy. The total stress was evaluated through the measurement of the substrate curvature, using a profilometer, while nanoindentation experiments helped determine the films' hardness and elastic modulus. The friction coefficient and the wear rates of the films were determined using a tribometer in unlubricated sliding friction experiments, while the critical load of failure was determined by a classical scratch test. The results showed that the use of the employed experimental setup and an amorphous silicon interlayer improved the a-C:H films' deposition onto steel substrates, producing good adhesion, low compressive stress, and a high hardness. The composition, microstructure, and mechanical and tribological properties of the films were dependent on the applied bias voltage. These results suggest that a combination of a modified pulsed-DC PECVD system, the use of an active screen as a cathode, and acetylene as a precursor gas for growing a-C:H films may represent a new and useful alternative for mechanical and tribological applications.