Copper is converted to cuprous oxide after being exposed to oxygen plasma treatment in a reactive ion etcher. X-ray diffraction indicates the formation of (111)-oriented cuprous oxide films. Films exhibit p-type conductivity with high carrier concentrations due to a large number of copper vacancies. The optical bandgap of 2.45 eV is significantly larger than reported bulk values of 2.0-2.2 eV. This blue shift is due to the small crystallite size of the film. (C) 2010 Elsevier B.V. All rights reserved.