Submonolayer island formation and the onset of multilayer growth during Ag/Ag(100) homoepitaxy

Results from a scanning tunneling microscopy study are presented for the initial stages of Ag/Ag(100) homoepitaxy, and behavior is analyzed via Monte Carlo simulations of an appropriate lattice-gas model. Submonolayer nucleation and growth of two-dimensional islands is examined for substrate temperatures, T, between 295 and 370 K. The variation with flux of the mean island density, N_av, reveals that island formation is effectively irreversible at 295 K, and leads to an estimate of 0.38 eV for the terrace diffusion barrier (using an attempt frequency of 10¹³/s). The variation of N_av with T reveals a transition to reversible island formation at around 320 K. This transition temperature (and the T-dependence of N_av) are used to extract an effective value of 0.3 eV for the bond energy of an adsorbed dimer, assuming nearest-neighbor pairwise-additive interactions between adsorbed atoms. We indicate how the actual dimer bond energy could differ, e.g. in the presence of biased diffusion of separated adatom pairs which enhances their recombination, and thus increases effective dimer stability. The onset of multilayer growth, and specifically the formation of second-layer islands, is examined at 295 K to assess the degree of interlayer transport. Comparison with simulations yields an estimate of 30 meV for the effective value of an additional step-edge barrier (using an attempt frequency of 10¹³/s). Using this result, subsequent multilayer kinetic roughening is predicted, consistent with experimental observations.