Growth and structure of ultrathin alumina films on the (1 1 0) surface of gamma -Al sub(4)Cu sub(9) complex metallic alloy

The first stages of oxidation of the (1 1 0) surface of a gamma -Al sub(4)Cu sub(9) complex metallic alloy were investigated by combining x-ray photoemission spectroscopy, low energy electron diffraction and scanning tunnel microscopy studies. Oxidation at room temperature in the 2 x 10 super(-8) to 2 x 10 super(-7) mbar oxygen pressure range occurs in two steps: a fast regime is followed by a much slower one, leading to the formation of a thin aluminium oxide film showing no long range order. Cu-O bonds are never observed, due to fast oxygen induced aluminium segregation. The low value of the estimated activation energy for aluminium diffusion (0.65 + or - 0.12 eV at super(-1)) was ascribed to the presence of two vacancies in the gamma -Al sub(4)Cu sub(9) structure. Annealing at 925 K the oxide film formed at room temperature leads to the formation of small crystallized domains with a sixton structure similar to structures reported in the literature following the oxidation of Cu-9%Al(1 1 1), NiAl (1 1 0) and FeAl(1 1 0) surfaces as well as ultrathin Al films deposited onto Cu(1 1 1) or Ni(1 1 1) surfaces. Two contributions were observed in the O1s peaks, which have been ascribed to loosely bound oxygen species and oxygen belonging to the sixton structure respectively.