Heterogeneous nucleation of binary alloy particles

Abstract

The nucleation and growth of alloy particles on substrates represent the initial stages of the formation of alloy thin films. Their structure and composition may be strongly influenced by the condensation behaviour of the individual components. We have investigated the cases of AuAg, AuPd, and AgPd on NaCl(100) cleavage surfaces at 300°C in uhv. It was found that the condensation coefficients of the single components decreased by roughly one order of magnitude in the sequence Pd, Au, Ag. Consequently, the composition of the nucleated particles differed considerably from that of the respective vapor beams. This difference increased in the sequence AuAg, AuPd, AgPd under otherwise equal conditions. In any case, it was found that the preferred nucleation of the component with the higher condensation coefficient increased the condensation coefficientof the other component. The results were interpreted by a suitably modified adatom diffusion model as well as by Monte Carlo calculations and this made it possible to determine differences of atomic energy parameters of the components with relatively high accurary. These parameters contain the energy of adatom adsorption and of surface diffusion, and were found to be consistent for the investigated triplet of alloys.