Microstructure evolution and wettability regulation of air-exposed hydrogen-free diamond-like carbon films

Abstract

Regulation of surface wettability is of vital significance to diamond-like carbon (DLC) serving as multi-functional coatings in many important fields. In this study, hydrogen-free DLC films with highly adjustable surface wettability induced by surface local hybridized structures were deposited on silicon substrates by RF magnetron sputtering under different substrate temperatures and RF powers. A non-monotonic dependency of surface wettability on the hybridization states, which is just inverse for polar and non-polar liquids, was found on the homogeneous DLC films with nanoscale surface roughness. In particular, the wetting transition from hydrophilicity to hydrophobicity occurred on the DLC films in contact with water. A clear picture about the essential correlation of surface wettability to microstructures of DLC films was drawn in terms of detailed analysis of surface energy components associated with the evolution of sp2-C bonds or clusters in content, type and distortion. Further, a possible mechanism accounting for the wetting transition of the DLC films was also proposed. This work aims to reveal the wetting nature of hydrogen-free DLC films versus graphite and diamond, and provide an available strategy to fabricate high-performance DLC films with special surface wettability used in aqueous environment.