The structure of passive film formed on Ti in pH 8.5 buffer solution was examined by comparing the photocurrent for both the passive film and the thermally grown oxide on Ti in air at 400 degrees C. The passive films formed on Ti in pH 8.5 buffer solution showed optical band gap energy of 3.36 eV, while the thermally grown oxide film on Ti was found to have band gap energy of 3.1 eV. The higher value of band gap energy of passive film was attributed to the less crystalline or more disordered structure of passive film compared to that of the therinal oxide. This fact was supported by the higher disorder energy of passive film, determined from the absorption tail of photocurrent spectrum, than that of thermal oxide. (c) 2006 Elsevier B.V. All rights reserved.