An extended Derjaguin-Landau-Verwey-Overbeek theory approach to determining the surface energy of copper oxide thin films prepared by reactive magnetron sputtering

Copper oxide films were sputter deposited on glass substrates by reactive rf magnetron sputtering, using a solid copper target and an argon-oxygen gas atmosphere. The films were characterized by scanning electron microscopy, atomic force microscopy, and spectrophotometry. The effect of input power and oxygen flow rate on the dispersive, polar, and acid-base (AB) components of the surface energy of the films was evaluated. The extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to analyze the factors controlling the interaction of copper oxide films with their environment. The components of the surface energy were determined by the Owens-Wendt and the Van Oss-Chaudhury-Good approaches, using water, ethylene glycol, and diiodomethane as the probe liquids. The Lifshitz-Van der Waals (LW) dispersive interaction force was found to be the major contributor to the surface energy of the films. In addition, we observed that other phases of copper oxide such Cu₂O and mixed Cu₂O/CuO are also hydrophobic. Black optically absorbing CuO has been previously identified as a hydrophobic phase. Transparent Cu₂O films hold substantial promise as antistiction coatings in micromirror arrays for micro-electromechanical systems applications. Copper oxide films also have potential aerospace applications as low friction coatings.