THE ALUMINUM SAPPHIRE INTERFACE FORMATION AT HIGH-TEMPERATURE - AN AES AND LEED STUDY

We report the heteroepitaxy of Al(111) on alpha-Al2O3(0001) realized at 470 degrees C by aluminium evaporation and characterized by Auger spectroscopy (AES) and low energy electron diffraction (LEED). This crystalline growth is preceded by suboxide formation due to the superficial oxygens of the sapphire substrate, and the nucleation of aluminium crystallites with a (111) surface randomly oriented around the (0001) axis. Epitaxial growth dominates with the relationship[($) over bar 211](111)Al parallel to(($) over bar 2110)(0001)Al2O3. Aluminium evaporation onto a sapphire crystal held at 720 degrees C generates a uniform etching of the substrate similar to the silicon-beam etching of sapphire, in contrast to what is observed for the re-evaporation of a room-temperature-grown Al layer which leads to a severely damaged surface, Increasing the growth temperature reduces the sticking coefficient of the aluminium on alpha-Al2O3(0001) and does not seem to affect the depth-limited character of the reaction. The results are discussed on the basis of the complex crystallographic structure of sapphire and its surface phase changes induced either by thermal treatments or reactive metal deposition. The sensitivity of Auger spectroscopy towards chemical shifts related to metal reaction is underlined.