Microstructure of the surfactantlike effect in Ni/Ag(100) and (111)

Recent experiments on Ni/Ag systems have shown that the growth mode can be a floating monosubstrate or bisubstrate layer burying the deposited film. We study this surfactant effect by both mean-field and Monte Carlo kinetic approaches. The kinetic tight-binding Ising model in mean-field approximation gives quasisteady profiles consistent with local equilibrium concepts. In this framework, we find two and one capping Ag monolayers for Ag(100) and Ag(111), respectively, on a mostly pure Ni monolayer. Monte Carlo simulations reveal that this Ni ''sandwich'' structure is in fact made of embedded Ni precipitates with low interface energy regular polyhedra shapes. The cluster distribution is found to be larger for the less compact surface [i.e., (100)] and to obey the ''Ostwald ripening'' law.