TRANSITIONS IN CRITICAL SIZE FOR METAL(100) HOMOEPITAXY

For submonolayer nucleation and growth of islands during metal (100) h omoepitaxy, we precisely characterize transitions, with increasing tem perature, 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 tet ramers are stable, but not, e.g., pentamers. A criterion is also prese nted for the ultimate breakdown of ''i=3'' due to double-bond scission . Various transition temperatures and key energies are thereby determi ned for Ag, Cu, Fe, Ni and Pd.