Formation of a well-ordered aluminium oxide overlayer by oxidation of NiAl(110)

Abstract

We have investigated the electronic and geometric structure of a thin oxide film grown by oxidation on NiAl(110) using electron spectroscopic techniques, i.e., LEED, EELS, XPS and ARUPS. This film is inert to adsorption of, respectively reaction with many molecules up to temperatures of about 800 K. It is well ordered as deduced from the LEED pattern and covers the whole surface. We find that the oxide film is about 5 Å thick, consisting of aluminium oxide as shown by EELS, XPS and ARUPS. It is most likely formed of two aluminium layers and two quasihexagonal oxygen layers with oxygen surface termination. Since the oxide film is rather thin it only shows a two-dimensional band structure which has been investigated using ARUPS. For the electronic levels of the oxide strong periodic dispersions are observed with bandwidths compatible to dispersion bandwidths calculated for the ΓX direction of α-Al2O3.