THE AU SI(111) SYSTEM STUDIED BY OPTICAL 2ND-HARMONIC GENERATION/

The room temperature growth of Au on Si(lll) 7 x 7 has been followed c ontinuously with second-harmonic generation, and at selected coverages with low energy electron diffraction and Auger electron spectroscopy, during the evaporation of the first 15 monolayers. A fast decay of th e second-harmonic signal in the submonolayer regime is associated with disordering of the 7 x 7 structure. This is followed by a local maxim um at about 1 monolayer coverage. The origin of this maximum is not ye t fully understood. In the range from 2 to 5 monolayers, the signal va riations reflect the formation of Au islands with areas of free Si in between. Above 5 monolayers second-harmonic generation shows increasin g order in the system which is ascribed to the creation of an ordered Au/Si interface, starting when a closed Au layer is formed. Annealing of the room temperature deposited Au layer leads to interface ordering even at low temperatures where no superstructure is observable with l ow energy electron diffraction.