Anodic oxide film growth on thin magnetron sputter-deposited titanium layer

A ~ 100 nm thick sputter-deposited titanium layer on electropolished aluminium is used for the investigation of anodic film growth in 1 M H3PO4. It is found that the thin titanium layer could not provide sufficient current efficiency for titanium anodic film growth when anodized to the voltage over 80 V due to the occurrence of oxygen evolution. The ruptures of titanium anodic film and the sputtering layer are induced by the development of oxygen bubbles. The penetrated phosphoric acid electrolyte in the ruptured regions of sputtering titanium layer contacts with the aluminium substrate, which is leading to the anodic oxide growth of aluminium. The thickness of the titanium anodic film increases from 10 to 100 V, however, it is reduced from 100 to 150 V due to the thinning of titanium layer. Over 80 V, the sputtering layer at some regions where it is completely ruptured, the anodic film growth of titanium could not be created. A thicker aluminium anodic film is formed on such regions due to the direct connection with the electrolyte.