Chemical alteration of thin alumina films on aluminum during hydrogen-atom exposures

Hot-rolled and partially oxidized Al foil surfaces were examined before and after H-atom exposures using X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) to monitor the changes which occur at the sample surfaces. The near-surface region of the native oxide of the hot-rolled Al foil contains primarily C and O. Cl and Ca contamination also are present at the outermost atomic layer according to ISS. H-atom exposures reduce the amount of carbonates and hydrocarbons but causes an enrichment of sulfur in the outermost layer of the foil. The O-to-Al ratio is reduced, and the AlOx species initially present is converted to Al2O3. After sputtering the Al foil to remove the Cl, C, and Ca contaminants, the Al was exposed to oxygen at 10−7 Torr for 10 min. The near-surface region of this re-oxidized surface contains both Al metal and Al2O3. Exposing this partially oxidized surface to H-atoms produces a chemically-induced driving force which causes subsurface O to migrate toward the surface of the foil. This results in an increase of the Al2O3 concentration at the sample surface. These results suggest that the thickness of Al oxide layers may be controlled using H-atom exposures. Furthermore, the amounts of carbon contamination can be decreased and possibly eliminated without reducing the alumina.