Enhancement of mechanical, tribological and morphological properties of nitrogenated diamond-like carbon films by gradient nitrogen doping

Abstract

Diamond-like carbon (DLC) films with gradient nitrogen (N) doping were synthesized by direct-current (DC) magnetron sputtering method. The effects of N doping on composition, adhesion, mechanical, tribological and morphological properties were investigated by Raman spectra, nano-scratch tester, nano-indenter and atomic force microscopy (AFM). The results of nano-scratch tester showed that the adhesion of DLC film was enhanced due to N introduction. The results of AFM, nano-scratch tester and nano-indenter showed that the doping method of gradient increased N component had a significant improvement in surface roughness and mechanical properties compared with the conventional N doping method. The gradient N doping (NG-DLC) films also exhibited better tribological properties compared to conventional N doping (NC-DLC) film. The adhesion and roughness were well achieved and improved simultaneously by utilizing a gradient N-doped deposition method for the first time. The relationship between tribological and mechanical properties was deduced and demonstrated. A model based on wave superposition theorem was built to interpret the relationship between surface roughness and N concentration during the deposition. The simulation results showed great agreement with the experimental results.