Electro-chemo-mechanical properties of anodic oxide (passive) films formed on Cu, Ni and Fe

Abstract Electro-chemo-mechanical properties of anodic oxide (passive) films formed on metals have been reviewed focusing on the results of stress variations caused by anodic oxidation of Cu, Ni, and Fe thin film electrodes in deaerated pH 8.4 borate buffer solution at 25 °C. The surface stress varies toward compressive direction due to adsorption of OH on Cu from aqueous solution as well as adsorption of oxygen on metals from gas phase. The stresses are generated with the growth of three-dimensional anodic oxide films on metals. The magnitude and sign (tensile or compressive) of the intrinsic film stress were determined by taking the residual stress of the substrate and the dielectrostriction into consideration. The tensile or compressive intrinsic film stress depends on p-type or n-type semiconductive properties of the anodic oxide films, which is explained in terms of the void formation or oxide formation in the metal side at the metal/film interface. Furthermore, the stress variation toward compressive direction during cathodic reduction of the anodic oxide films is explained in terms of the volume expansion due to the formation of intermediate species.