Interaction of oxygen with Ni3Al(111) at 300 K and 1000 K

We have investigated the oxidation of Ni3Al(111) at 300 K and 1000 K with STM and work function change measurements. Oxygen exposure at 300 K initially increases the work function, indicating oxygen chemisorption. Exposures above 5 L lead, however, to a rapid decrease of the work function, indicative of oxygen incorporation. This process is accompanied by a strong surface roughening which leads to a disordered surface. Annealing this surface at 1000 K results in the formation of "strawberry"-shaped oxide islands on the substrate terraces. Adsorption of oxygen at 1000 K produces a well-ordered oxide phase that gives rise to a Moire pattern with a periodicity of 2.5 nm. This pattern disappears for bias voltages below similar to 3 V, accompanied by a strong decrease in the apparent height of the oxide layer. This effect can be explained in terms of the band gap of the alumina layer. (C) 1999 Elsevier Science B.V. All rights reserved.