On the Relation Between Growth Instabilities and Internal Stress Evolution during Galvanostatic Ti Thin Film Anodization

Abstract

Sputtered Ti thin-film electrodes have been anodized, both continuously and in an interrupted way, under galvanostatic conditions in 1.0 M H2SO4 up to forming voltages in the range of 5-40 V. The internal stresses developing in the anodic oxide film have been followed in situ during anodizing using a high-resolution curvature measurement technique. The observed stress evolution is discussed in relation to the oxygen evolution reaction and other growth instabilities previously reported in the literature. The onset of the oxygen evolution reaction, which significantly reduces the growth efficiency, is observed to induce very large compressive stresses. The latter are likely to result from oxygen evolution inside the oxide film. At some stage during film growth, the growth efficiency is observed to return to its initial high value, and the instantaneous stress in the film changes from compressive to tensile. A tentative explanation is proposed for the observed phenomena, taking into account the kinetics of the oxygen evolution reaction inside the film. (C) 2008 The Electrochemical Society.