Transitions in critical size for metal(100) homoepitaxy

For submonolayer nucleation and growth of islands during metal (100) homoepitaxy, we precisely characterize transitions, with increasing temperature, in the critical size, i, above which islands are effectively stable. For strong adatom bonding, we demonstrate universal crossover behavior from i=1 directly to a well-defined ''i=3'' regime where tetramers are stable, but not, e.g., pentamers. A criterion is also presented for the ultimate breakdown of ''i=3'' due to double-bond scission. Various transition temperatures and key energies are thereby determined for Ag, Cu, Fe, Ni and Pd.