The influence of different silicon adhesion interlayers on the tribological behavior of DLC thin films deposited on steel by EC-PECVD

Diamond-like carbon (DLC) is a hydrogenated amorphous carbon (a-C:H) thin film material owing to its unique tribological properties that may open great opportunities for new applications. However, DLC presents low chemical affinity with metallic alloys and high intrinsic stress, prompting film delamination and poor adherence on the substrate. In the present work, we performed a systematic study about structural and tribological properties of a-C:H thin films grown on steel by introducing adhesive silicon-containing interlayers deposited at different processing temperatures and times. The studied bi-layers were deposited by electrostatic confinement plasma enhanced chemical vapor deposition (EC-PECVD) and were characterized by several techniques. The results showed that the adhesive interlayers produced from tetramethylsilane are chemically structured as a non-stoichiometry hydrogenated amorphous silicon carbide alloy (a-SiCx:H). Its structure, chemical composition and thickness are very dependent on deposition conditions. The thickness of the interlayers increases with deposition time and decreases with deposition temperature. The interlayer contains less hydrogen and silicon atoms at higher deposition temperatures, with enhanced formation of Si-C bonds in its structure. This last chemical event is correlated with the rise in the critical load values found for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 573 K to 823 K. On the other hand, the interlayer contains less carbon atoms at higher deposition times, decreasing the critical load values for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 5 min to 10 min.