Comparative study on structure and wetting properties of diamond-like carbon films by W and Cu doping

Abstract

By specifically selecting the carbide-forming metal (W) and non-carbide-forming metal (Cu) as the doped metal, we fabricated the W and Cu doped diamond-like carbon (W-DLC and Cu-DLC) films by hybrid ion beam system, respectively. And a comparative study on structure and wetting properties of W-DLC and Cu-DLC films was focused. For Cu-DLC films, the wettability transformation from hydrophilicity (76.56°) to hydrophobicity (105.6°) was observed. While in case of W-DLC films, the wettability of films maintained the hydrophilicity (73.6±3.93°) within the presented W concentration. Based on the surface energy calculation and electronic structure analysis from first-principles calculations, we firstly gained insight into the wettability behavior of W-DLC and Cu-DLC films in terms of the bond characteristics formed between doped metal and C atoms. Results showed that the anti-bonding characteristic between Cu and C atoms reduced the polar components of surface energy and dangling bonds, contributing to the improvement of hydrophobic property, while the non-bonding characteristic for WC bond resulted in the appearance of dipoles, leading to the hydrophilic character. It was in particularly concluded that the different bond characteristic between metal and C atoms played a key role in the wettability of metal doped DLC films. The obtained results offer a facile strategy to design DLC films with tailored wettability properties for the promising hydrophobic applications.