Extra-relaxation effects in ultra-thin Al2O3 films on metal substrates

The oxidation of NiAl(110) was investigated in the temperature range betwee n 300 K and 1300 K by using Anger electron spectroscopy, X-ray photoelectro n spectroscopy, and low energy electron diffraction. The adsorption of N2O an clean NiAl(110) at 300 K leads only to selective oxidation of the surfac e aluminium without any apparent surface reconstructions. Stepwise annealin g of the heavily oxygen-doped samples from 600 K to 1300 K in ultra-high va cuum results firstly in the onset of randomly oriented oxide surface then f inally fairly well-ordered Al2O3 films. The much wider energy separation be tween the core (or Auger transition) levels of metallic Al-0 and oxidic Al3 + states for thicker oxide films is believed to be due to a lower degree of extra-relaxation by metallic electrons and, therefore, would, imply better quality for oxide films with similar thicknesses.