Growth and structure of ultrathin alumina films on the (1 1 0) surface of γ-Al4Cu9 complex metallic alloy

Abstract

The first stages of oxidation of the (1 1 0) surface of a γ-Al4Cu9 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 × 10−8 to 2 × 10−7 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 ± 0.12 eV at−1) was ascribed to the presence of two vacancies in the γ-Al4Cu9 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.