THE AL/AL2O3 INTERFACE FORMATION AS STUDIED BY ELECTRON SPECTROSCOPIES

The Al Al2O3(0001) interface formation has been investigated by low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS), X-ray induced photoemission spectroscopy (XPS) and Auger electron spectroscopy (AES). Aluminium reacts at the surface of alumina, giving rise to an aluminium-rich substoichiometric surface region, after a limited diffusion into the first atomic layers. At this point, a ( 31 × 31)R ± 9° reconstruction is observed by LEED, indentical to the diagram which is obtained after heating stoichiometric alumina above 1250°C. For coverages larger than 5 monolayers, metallic Al lines appear, the surface becomes rough, and the LEED patterns disappear due to charging effects. These observations are related to the formation of Al clusters above 5 monolayers. Further metal deposition leads to island growth and, for several tens of angstroms, the metallized surface becomes smooth again. The Al2O3(0001) Fuchs-Kliewer phonons are decreasing with increasing aluminum coverage. Theoretical considerations show that the presence of a uniform metallic layer on top of an ionic crystal such as Al2O3(0001), with a sharp unreacted interface, would immediately screen the surface modes of the substrate. © 1990.