Reversible Optical Changes Within Anodic Oxide Films on Titanium and Niobium

Abstract

During passage of cathodic current, large and reversible changes in ellipsometric parameters are interpreted in terms of changes in absorption and/or refractive index of surface anodic oxide films on Nb and Ti without significant change in thickness. A model based on dissolution and ionization of deposited hydrogen satisfactorily accounts for the slow reversible change in the optical absorption of films on Nb and for the impedance changes previously reported. More rapidly reversible changes in both absorption and refractive index occur in films on Ti. The decrease in refractive index is consistent with the reversible formation of at negative potentials.