Improving the mechanical property of amorphous carbon films by silicon doping

The aim of the present work was to optimise the deposition process of a-C:Si films and to establish the relationships between the structure, surface morphology, elementary and phase composition and the mechanical and tribological properties with respect to the C/Si ratio in the films. The a-C:Si films were formed via sputtering a composite silicon-graphite target by pulse arc discharge. The C/Si atomic concentration ratio was changed varying the C/Si mass concentration ratio of the cathode. Raman spectrometry showed that Si doping leads to a reduction in size of Csp(2) clusters and to an increase of degree of disorder in the film structure with increasing the Si concentration. XPS analysis revealed the presence of the C-Si bonds in the films, which are typical for silicon carbide, with Csp(2)/Csp(3) reducing at the increase of Si concentration in the film. It has been shown that the doping of the a-C films with Si results in decreased both the residual stresses and the surface energy, and influences the films friction kinetics, primarily friction coefficient. In general, the a-C:Si films properties depend on the silicone concentration and the certain Si concentration threshold value can provide the surface microstructure stabilisation, which is dealt with the graphitisation temperature increase, presumably due to SixOy formation at the film surface that leads to the improved tribological properties of the a-C:Si films.