Superstructures on thin Al2O3 grown on Ni3Al(0 0 1)

Thin ordered layers of Al2O3 grown on a metallic Ni3Al(0 0 1) substrate were studied using UHV STM and LEED. The oxidation of the substrate at 800 K and 1100 K forms different structural phases of Al2O3. Oxidation of Ni3Al(0 0 1) at 800 K leads to a simple surface pattern, while oxidation at 1100 K results in a variety of surface patterns revealing superimposed quasi-periodic superstructures larger than expected from a simple moiré model. Atomic resolution achieved with STM on the Al2O3 surface allows us to determine all possible mutual orientations of the crystalline lattices. The spectroscopic STM dI/dV plots indicated different electronic properties at various points on the oxide superstructure. We conjecture that they can be attributed to ordering of structural patches distributed in a regular way.