Microstructure and wettability of novel Al-containing diamond-like carbon films deposited by a hybrid sputtering system

Abstract Al-doped diamond-like carbon (DLC) films having various Al contents were fabricated by a co-sputtering system. The designed Al target power was increased from 10 to 70 W to obtain different Al contents. The effect of Al content on the surface morphologies, carbon bonding structure, residual stress, and the wetting property of films was systematically investigated. The results show that the Al content in films increased with increasing the sputtering power of Al target, and the surface roughness of the films increased with increase of Al content. It was also found that the carbon bond, including sp2─C and sp3─C bonds, was a function of the Al content. The sp2─C bond fraction and the ratio of sp2/sp3 increased with increasing Al content, implying more graphitization in the films. Meanwhile, the residual stress of films decreased by adding Al content. In addition, the contact angles of the films increased from 68.8° for the pure DLC film to 107.7° for the film with moderate Al doping, implying that the wettability of the films transformed from the hydrophilicity state to the hydrophobicity state. Accordingly, the surface energy of the films decreased from 42.45 to 18.43 mJ/m2. This change was attributed to the improved sp2-C bond fraction and surface roughness of the films. The findings of this study provide a feasible method of designing and fabricating DLC films with low residual stress and controllable wettability properties.