The effect of deposition parameters on the properties of gradient a-C:H/Ti layers

Purpose: During the last 20 years DLC (diamond-like carbon) layers became a very attractive material in many medical and engineering applications. While the layer’s stress and adhesion were always a concern, several adhesion improvement methods have been proposed. A majority of those methods consists of either the deposition of an adhesion promoting interlayer or the application of a gradient of chemical composition. In whatever way this reduces the internal stress and improves the adhesion of carbon layers, it also affects the properties of the carbon layer. The aim of this study was to investigate the physicochemical properties of gradient carbon layers manufactured by RF PACVD/MS method at different process parameters. Design/methodology/approach: The a-C:H/Ti gradient layers were deposited onto silicon wafers using a hybrid deposition method which combines PVD and CVD processes in one reaction chamber. Surface topography, adhesion and coefficient of friction (COF) were measured at a nanoscale using Atomic Force Microscopy, Nanoindentation, and Nanotribometry. Findings: The result of this investigation has demonstrated that gradient interlayer deposition parameters affect roughness and tribological properties of outer carbon layer. Research limitations/implications: Presented investigation was performed with mirror-polished silicon wafers to prevent possible interferences caused by variations in surface topography of other typical substrates during polishing. However, the adhesion of carbon layer measured for the silicon substrates can be noticeably different from that measured for metal substrates. Thus, new adhesion investigations have to be done when using these layers on application-specific substrates. Also, additional friction and wear resistance measurements performed under wet conditions (biological serum) should be conducted in a case of medical applications. Originality/value: There are several reports available on the properties of carbon layers deposited subsequently onto the adhesion promoting interlayer. Present work is an attempt to understand and describe influence of adhesion promoting interlayer deposition parameters on the properties of interlayer - layer system as a whole.