Nucleation and growth of metallic submonolayers on compact metal surfaces

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Abstract
By use of the molecular-dynamics method we study the high-temperature nonequilibrium and equilibrium properties of a metallic overlayer on a compact metal surface. The system is modeled by the embedded-atom method, and consists of a Pt slab with a large ideal (111) surface (cross section of 930 atoms) on which Ag atoms are randomly distributed with coverages FTHETA=0.10, 0.25, 0.30. We simulate the short-time (τ∼1 ns) process by which the adatoms form dynamically stable aggregates in local equilibrium with a dilute two-dimensional vapor. We analyze the equilibrium properties of the adlayer as a function of T and FTHETA. We compute the cluster size distribution, the adatom radial-distribution function, the diffusion coefficient, and we characterize the cluster shape by the ratio of its principal moments of inertia. At all FTHETA and T the Ag islands grow pseudomorphically on Pt(111). At high temperatures (T∼1000 K) the clusters are fluidlike. There is no evidence of peculiar stability at the sizes corresponding to the filling of two-dimensional close-packing shells (‘‘magic numbers,’’ N=7, 10, etc.). At intermediate temperatures (T=600–800 K) the size distribution is shifted toward larger aggregates and, at low coverage, starts to display stability peaks at the magic numbers. The larger clusters develop a solidlike core surrounded by a fluidlike boundary. At the lowest temperature of our study (T=400 K) the clusters display a high degree of local order. The size distribution function is restricted to small N’s by the slowing down of the cluster growth beyond the nucleation stage. At FTHETA=0.10 the stability peaks at N=7 and 10 are apparent. We discuss the influence of a step on the behavior of the system.

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