Microstructure and mechanical properties of CeO2 doped diamond-like carbon films

A kind of rare earth oxide, CeO2, was doped into the diamond-like carbon (DLC) films with thickness of 180–200 nm, using unbalanced magnetron sputtering. All the adhesion strength of CeO2 doped DLC films is increased, while the residual compressive stress is obviously decreased compared to pure DLC film. Specially, the residual compressive stress of the deposited films are reduced by 90%, when the CeO2 content is in the range of 5–7%, from a value of about 4.1 GPa to 0.5 GPa. When the CeO2 content is increased to 10%, the deposited films possess the highest adhesion strength of 85 mN, 37% higher than that of pure DLC film. The nanohardness and elastic modulus exist a transition point at 8% of CeO2 content within the DLC film. Before this value, nanohardness and elastic modulus of CeO2 doped DLC films are lower than those of pure DLC film, and after this value, they are higher or adjacent to those of pure DLC film. Auger electron spectroscopy shows a more widened interface of 6% CeO2 doped DLC film compared to pure DLC film. The enhancement of adhesion strength is mainly attributed to the widening of the film-substrate interface, as well as the decrease of residual compressive stress.