Accelerated wetting transition from hydrophilic to hydrophobic of sputtered Cu films with micro-scale patterns

Abstract Hydrophobic surfaces have attracted increasing interest due to their versatile applications. Recently, hydrocarbon adsorption and its influence on the wettability has aroused great attention, some hydrophilic surfaces could turn into hydrophobic with gradual adsorption of organic compounds from ambient air. In this work, we demonstrated that micro-square holes can effectively accelerate and magnify the wetting transition, reducing the transition period of sputtered Cu films from hydrophilic to hydrophobic, finally, water droplet pinned tightly to the film surfaces. XPS results revealed that hydrocarbon adsorption caused an obvious increase in surface C content, which contributed further to the hydrophobicity enhancement and surface energy decrement over exposure time. To clearly explain the accelerated transition mechanism, we discussed extensively how the wetting on patterned Cu films evolved. Calculations according to the Wenzel and Cassie-Baxter theory showed that the final wetting state on patterned Cu films was in Cassie-Baxter regime and the holes were responsible for the observed transition. This study not only provides deep insights into the wetting transition mechanism of sputtered Cu films, but further guides how to effectively achieve stable hydrophobic surfaces with adhesive properties through rationally designed patterns.