Surface films formed on aluminum by different pretreatments. I. XPS analysis of thickness and chemical composition.

Pure aluminum was a) electropolished in HClO4/CH3COOH solution (E.P.)or b) chemically polished in HNO3/H3PO4 solution (C.P.) or c) immersed in H3PO4/CrO3 solution after treatment E.P. or C. P.. The films formed were analyzed by XPS to estimate thickness and chemical composition.It was found that the thickness of the films was in the range of about 3.5 to 5.0nm, and that appreciable amounts of electrolyte anions were included in the films. Except for phosphate the electrolyte anions included were found to be in reduced form.The films formed by electropolishing consisted of aluminum oxide with small amounts of OH- (or H2O) and Cl- ions, while those formed by chemical polishing included NO2- and PO43- ions.Immersion in H3PO4/CrO3 caused the Cl- and NO2- ions to disappear from the surface and films included high concentrations of OH- (or H2O), CrIII and PO43- ions.