Oxygen evolution within barrier oxide films

Abstract Using residual gas analysis, with scraping of oxide films, it is demonstrated that oxygen gas can be generated within anodic films on Al–Cu alloys and InP. The oxygen is produced by oxidation of O 2− ions of the film material, and is present in numerous bubbles in the bulk film. The generation of oxygen is suggested to be related to the electron energy levels of the film material, which in the case of alumina films are modified by the incorporation of copper species and, from previous work, other non-valve, transition metal species. Oxygen is also present in low amounts in alumina films nominally free of the latter species; the oxygen may be located either in the bulk oxide or at flaws.