ELECTRON MOMENTUM SPECTROSCOPY STUDIES ON THE OXIDATION OF ALUMINUM

Electron momentum spectroscopy has been used to measure the electronic structure of aluminium after exposure to increasing amounts of oxygen . The experimental valence band results showed the structural features of aluminium oxide beginning to dominate the free electron contributi on of metallic aluminium as the exposure increased. The interpretation of this is that the aluminium oxide layer increases in thickness as t he exposure increases, eventually saturating at a thickness of about 5 Angstrom. After subtracting the intensity of the underlying Al metal contribution from the oxidised states the valence band features of alu minium oxide were resolved even after exposure to only 600 L of oxygen . It is estimated that only about 5 A of aluminium oxide is formed at this stage. A quantitative comparison was made to a linear muffic-tin orbital (LMTO) calculation for spherically averaged alpha-Al2O3. Best agreement was obtained for the results of the lowest oxygen exposure ( 600 L). The chemical shifts of the Al 2p core level were also measured in separate experiments for two intermediate oxygen exposures between the aluminium and aluminium oxide cases for further characterisation. These measurements show that electron momentum spectroscopy is able t o obtain the electron bands and the momentum densities of very thin di sordered surface layers. (C) 1997 Elsevier Science B.V.