Tailoring the structure and property of silicon-doped diamond-like carbon films by controlling the silicon content

Diamond-like carbon (DLC) films have been extensively studied over the past decades due to their unique combination of properties; in particular, silicon-doped DLC (Si-DLC) films are of significant interest for tribological effects. But there are contradictory reports in the literature with regard to the effect of silicon content on the properties of DLC films. In this study, Si-DLC films were deposited by hollow cathode plasma immersion ion implantation (HCPIII) method, using mixtures of C2H2, Ar and diluted SiH4 (SiH4/Ar 10:90). The influences of Si addition on the surface morphology, structure, mechanical and tribological properties were investigated by a combination of surface analysis methods, nanomechanical and friction measurements. It was observed that addition of Si into DLC films lead to a decrease in the Raman band intensity ratio ID/IG. The root mean square values of Si-DLC films were increased along with the increase of Si concentration. Both the hardness and elastic modulus suffered degradation when the silicon concentration was low, but these properties recovered when Si concentration increased. The Si-DLC film with tensile stress and compressive stress can be obtained by choosing distinct contents of Si in the film. The coefficient of friction (COF) of Si-DLC films against GCr 15 steel ball under atmosphere firstly increased as the Si concentration increased up to 8.41 at.%, then COF of Si-DLC films decreased with a further increase of Si concentration. The mismatch in the bond length, the difference of the mechanical property and the alteration of the colliding particles' energy were determined to be the basis for the changes in these properties.