THE INTERACTION OF NI ADSORBATE WITH THE AG SI(111) SURFACE/

The change of atomic structures and compositional ratios by isochronal annealing of Ag-Ni binary adsorbates at the Si(111) surface has been studied by means of LEED-AES-RBS techniques at temperatures from 200 d egrees C to 700 degrees C. It is found that the surface coverage of Ni deposited on the Si(111)-root 3 X root 3-Ag surface decreases to 0 ML on annealing at 250 degrees C for 15 min, while the Ag surface covera ge is not changed by Ni deposition and subsequent annealing up to 350 degrees C. It is also found on annealing at 350 degrees C that Ag on t he Si(111)-root 19 X root 19-Ni surface produces the root 3 X root 3 L EED pattern and the Ni coverage by AES decreases to 0 ML. These result s indicate that Ag and Ni atoms are not bound to each other on the Si( 111) surface, and that Ag atoms preferentially occupy the surface with forming the root 3 X root 3-Ag structure and Ni atoms dissolve into t he Si bulk. Moreover, it is found that the room temperature deposition of Ni onto the Si(111)-3 X 1-Ag surface produces a mixed structure of root 3 X root 3 and 3 x 1, which is changed into the single root 3 X root 3 structure by subsequent annealing at 200 degrees C. It indicate s that Ag atoms move from the 3 x 1-Ag site into the root 3 X root 3-A g site due to the co-existence of Ni adsorbates.