Oxygen-induced migration of Ag nano-clusters on Si(111)-7 X 7 surface

The oxygen-induced migration of Ag clusters on Si (111)-7 x 7 surface was observed by in-situ STM. All experiments were carried out in UHV system. The Si (111)-7 x 7 surface was obtained by directly heating to 1200 degreesC for several times. At the beginning of Ag clusters growth on the Si (111)-7 x 7 surface, Ag clusters formed the uniform and well-ordered arrays on the surface. The monomers, dimers and clusters of Ag were observed. After exposure to oxygen, some Ag clusters vanished and conglomerated into bigger clusters. As known, there are two kinds of adsorbed oxygen species on the Si surface, ad-ins and ins-ins. The Ag clusters appear to move easily on the surface until being trapped by adsorbed atomic oxygen and pinned around the adsorbed oxygen. It was confirmed that the migration of Ag clusters is caused by oxygen decoration. The statistical results show that the Ag clusters diffuse much easily on partly oxidized Si (111)-7 x 7 surface than on Si (111)-7 x 7 surface. It was also found that the strong interaction between Ag cluster and adsorbed oxygen species causes a distinct change of the property of adsorbed oxygen, i.e. a change of surface ins-ins oxygen into ad-ins oxygen species, reflecting the role of substrate at room temperature.