Thickness determination of thin anodic titanium oxide films

The determination of oxide film properties as the relative permittivity epsilon r requires knowledge of the film thickness. Coulometry, as well as visible reflectometry, are fast and simple methods for determining the thickness of thin anodic oxide films on Titanium (99.9%) and a titanium alloy (TiAlV6-4). A comparison of the results shows the specific disadvantages and limitations of each method. On the one hand, the reflectometry yields a too-small film thickness and the authors therefore developed a simple correction algorithm for the reflectometric data. On the other hand, coulometry is not suitable as a thickness determination in the case of side reactions such as oxygen evolution. However, the complementary approach to the thickness determination, by using both reflectometry and coulometry, brings reliable thickness values of visible reflectometry down to >=5 nm. Furthermore, the comparison between coulometry and reflectometry allows the estimation of the current efficiency when the oxide formation is attended by side reactions.