POTENTIAL MODULATED REFLECTANCE SPECTROSCOPY OF ANODIC OXIDE-FILMS ON TITANIUM

Potential modulated reflectance (PMR) spectroscopy has been used to investigate thin anodic oxide films formed on titanium in sulphuric acid. The origin of the reflectance modulation is discussed and the experimental results are compared with theoretical calculations based on the three layer model. The overall shape and the dependence of the PMR spectra on film thickness have been modelled satisfactorily by assuming that the band gap of the oxide in the presence of an electric field is increased due to dielectric polarisation. The potential dependence of the modulated reflectance response for films of constant thickness was related to the electric field distribution in the oxide and the analysis showed that the modulated reflectance response is dominated by electroabsorption. The results demonstrate that PMR spectroscopy offers a more reliable method than Mott-Schottky plots for determining the flat-band potential of the oxide. © 1990.