STM STUDY OF ROOM-TEMPERATURE ADSORPTION OF AU ON THE SI(111)-(7X7) SURFACE - EVIDENCE FOR THE REACTION OF AU ATOMS WITH SI REST ATOMS

The initial stages of Au adsorption at sub-monolayer coverages on the Si(111)-(7 x 7) surface at room temperature have been studied by scann ing tunneling microscopy (STM). At very low Au coverages (Theta simila r to 0.01 monolayers) STM images show that some of the triangular sub- unit cells have slightly larger apparent height. These peculiar featur es are interpreted as being caused by the redistribution of charge in the 7 x 7 unit cell following the adsorption of Au atoms on Si rest at om sites. STM images suggest that there is a charge transfer from the rest atoms to the adatom and this charge transfer is different in faul ted and unfaulted sub-unit cells. The interpretation of the STM result s is found to be consistent with the theoretical predictions.