ELECTRONIC AND CRYSTALLOGRAPHIC STRUCTURE OF GAMMA-ALUMINA THIN-FILMS

We have investigated the crystallographic and electronic structure of gamma-alumina surfaces obtained by thermal oxidation of Al foil. By co mbining X-ray photoelectron spectroscopy, electron energy loss spectro scopy, transmission electron microscopy and transmission electron diff raction investigations, we have shown that such gamma-alumina surfaces are mainly (100), (1 $($) over bar$$ 10) and (112) oriented and are c haracterized by a specific electronic structure in the band gap. The a ppearance of defect levels decreases the gap from 8.7 eV to 2.5 eV at the surface. These features are correlated to the ionicity of the gamm a-alumina surface and could explain their chemical activity (i.e. acid o-basic properties).