INITIAL-STAGES OF AU ADSORPTION ON THE SI(111)-(7X7) SURFACE STUDIED BY SCANNING-TUNNELING-MICROSCOPY

Initial stages of Au adsorption up to coverage of Theta similar to 3 m onolayers (ML) on the Si(111)-(7 x 7) surface at room temperature (RT) have been studied by scanning tunneling microscopy (STM). At very low Au coverages (Theta similar to 0.01-0.05 ML) STM images show that som e of the triangular subunit cells have slightly larger apparent height which is interpreted to be due to the adsorption of Au atoms on the S i rest atom sites. At higher coverages (Theta>0.1 ML) small Au cluster s form preferentially on top of the Si center adatoms and,;to a less e xtent, on top of the Si corner adatoms. Stacking fault does not have a n appreciable effect on Au adsorption in this coverage regime. The res ults for Au are compared to the data on the adsorption of other metals on the Si(111)-(7 x 7) surface and mechanisms governing preference of the adsorbates for a particular bonding site are discussed.