Photostimulated anodic oxide film formation

An explanation of the photostimulated formation of anodic oxide films is given in terms of the photoquenching of the internal electric field. A description of this phenomena is presented within the framework of the point defect model. For the stationary situation, concentration profiles for oxygen ion vacancies across the film, in the dark and under super band-gap illumination conditions, are derived. For the nonstationary case a transport model is presented that accounts for the observed linear dependence of the film thickness L(t) on √t for the photostimulated formation of anodic films on zirconium in (1 M) H3PO4. This model can be used to derive the product of the diffusion coefficient of the oxygen vacancies DO and changes in their concentration at the metal/film interface. With DO=5×10−17 cm2 s−1, a change in the m/f interfacial oxygen vacancy concentration of 3.4×1022 cm−3 is found.