CHEMICAL ALTERATION OF THIN ALUMINA FILMS ON ALUMINUM DURING HYDROGEN-ATOM EXPOSURES

Hot-rolled and partially oxidized Al foil surfaces were examined befor e and after H-atom exposures using X-ray photoelectron spectroscopy (X PS) and ion scattering spectroscopy (ISS) to monitor the changes which occur at the sample surfaces. The near-surface region of the native o xide of the hot-rolled Al foil contains primarily C and O. Cl and Ca c ontamination also are present at the outermost atomic layer according to ISS. H-atom exposures reduce the amount of carbonates and hydrocarb ons but causes an enrichment of sulfur in the outermost layer of the f oil. The O-to-Al ratio is reduced, and the AlOx species initially pres ent 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) Tor r for 10 min. The near-surface region of this re-oxidized surface cont ains both Al metal and A1(2)O(3). Exposing this partially oxidized sur face to H-atoms produces a chemically-induced driving force which caus es subsurface O to migrate toward the surface of the foil. This result s in an increase of the Al2O3 concentration at the sample surface. The se results suggest that the thickness of Al oxide layers may be contro lled using H-atom exposures. Furthermore, the amounts of carbon contam ination can be decreased and possibly eliminated without reducing the alumina. (C) 1998 Elsevier Science B.V.