Growth of high-density small Ag islands on the Si(111)7x7 surface with adatom defects

We studied the growth of Ag islands on the Si(111)7 x 7 surfaces with missi ng adatoms created by 0.5-keV Ar-ion bombardment. Ag atoms were deposited a t room temperature, and the growths were observed by using scanning tunneli ng microscope. In the initial stage, bright spots including several Ag atom s appeared on triangular half unit cells of the 7 x 7 reconstruction. The s pots appeared as to avoid missing adatom sites. As the coverage increased, the number of the spots increased, and occasionally spots in neighboring ce lls kissed to form clusters. At similar to 0.8 monolayer, the surface was m ostly covered by the clusters of kissing spots, but the avoiding growth of the spots at the missing adatom sites caused gaps between the clusters here and there. In further deposition, three-dimensional (3D) Ag islands starte d to nucleate on the clusters. The size and density of the 3D islands stron gly depended on the number of missing adatoms at the initial surface. With an increase of missing adatoms, the island size decreased while the island density increased drastically. The change in the island size and density we re attributed to the substantial increase of the density and the reduction of the surface migration of the Ag atoms due to the gaps. [S0163-1829(99)12 143-X].