The oxidation of the NiAl(111) surface

The oxidation of NiAl(111) was investigated in the temperature region between 300 and 1500 K by HREELS (high resolution electron energy loss spectroscopy), AES (Auger electron spectroscopy) and LEED (low energy electron diffraction). The adsorption of oxygen up to saturation at room temperature leads to the formation of a thin amorphous Al-oxide film. After annealing the oxygen-covered sample to temperatures between 900 and 1100 K a well-ordered Al-oxide with hexagonal symmetry is found. The HREEL spectrum exhibits losses at 53, 79 and 110 meV. This suggests the formation of thin ordered gamma'-Al2O3 films on the surface. After annealing the sample above 1100 K the HREEL spectrum exhibits only two losses at 78 and 113 meV which are attributed to thin alpha-like Al2O3 layers. These Al-oxide overlayers contain less oxygen and the surface is facetted. The surface consists in (111) terraces and (110) facets which form triangular pyramids.