Effect of ultra-violet light irradiation on anodic oxide films on titanium in sulfuric acid solution

Photo-corrosion of a 9.2 nm thick oxide film of TiO2 formed anodically on titanium was studied in 0.1 M sulfuric acid solution by in-situ ellipsometry during 325 nm ultra-violet (UV) light irradiation. The UV light irradiation induces a change of the oxide film which is observed by ellipsometry. From the change of the ellipsometric parameters, the thickness decrease of the oxide film is estimated. The results estimated indicate that 5% of photo-induced current is consumed for photo-corrosion of the oxide film. The photo-corrosion rate is proportional to the positive bias relative to the flat-band potential and to the UV light intensity. The mechanism of the photo-corrosion is discussed for the photo-effect of an n-type semiconductive oxide electrode: the photo-corrosion is induced by an accumulation of photo-excited holes at the oxide surface, probably because the accumulation may increase the interfacial potential difference at the oxide|solution interface and weaken the Ti-O bond of the oxide.