Ion migration and film morphologies in anodic alumina films formed in selenate electrolyte

Film morphologies and ionic migration are investigated for anodic oxides formed galvanostatically on electropolished aluminum in selenate electrolyte. Anionic selenium species that migrate at ∼0.2 to 0.3 times the rate of O2- ions were present in barrier films. Further, porous films could be generated by the use of sputtering-deposited aluminum substrates, although the film thickness is limited to ∼70 nm. Re-anodizing in pentaborate electrolyte at high efficiency revealed also a cationic selenium species that migrates at ∼0.6 to 0.7 times the rate of Al3+ ions, suggesting that the migration of selenium is affected by the morphology and growth mechanism of the film. © 2012 The Electrochemical Society.