An investigation of the surface energy and optical transmittance of copper oxide thin films prepared by reactive magnetron sputtering

Copper oxide films have been sputter deposited on glass substrates by reactive radio frequency (rf) magnetron sputtering, using a solid copper target and an argon-oxygen gas atmosphere. The films were characterised by scanning electron microscopy/energy dispersive analysis of X-rays, X-ray photoelectron spectroscopy, atomic force microscopy, profilometry, spectrophotometry and surface energy measurements. The effect of input rf power and oxygen flow rate during deposition on the dispersive, polar and acid-base components of the surface energy of the copper oxide films was investigated. The components of the surface energy were determined by the Owens-Wendt and the Van Oss-Chaudhry-Good method. The Lifshitz-van der Waals dispersive interaction force was found to be the major contributor to the surface energy of the films and the origin of their hydrophobicity. Optical transmission in the prepared films was measured by spectrophotometry in the 400-850 nm wavelength region. We observed a maximum transmission of between 40% and 80% for copper oxide films prepared at a low rf power of 200 W, for the oxygen flow rates investigated. The optical bandgap values of the films ranged between 2.4 and 2.05 eV. The dependence of the optical properties of the films like optical transmittance and optical bandgap on deposition parameters like input rf power and physical properties like thickness and roughness was investigated in the wavelength range 400-850 nm. This information is expected to underlie the successful development of durable copper oxide films for technological applications requiring controlled optical transmission in the visible.