Diffusion and evaporation kinetics of large islands and vacancies on surfaces

The diffusion and evaporation kinetics of two-dimensional islands and vacan cy islands on surfaces are studied over a wide range of island sizes. These kinetic processes are central in surface phenomena such as thin film coars ening, island aggregation, and coalescence on surfaces. Several studies hav e utilized scaling theories to infer the atomic level mechanisms responsibl e for the kinetics of island diffusion and evaporation. Using a dynamic Mon te Carlo model, we study a model system where two-dimensional islands diffu se via an evaporation-condensation mechanism on a face-centered-cubic (100) surface. We examine the diffusion (evaporation) kinetics for isolated isla nds as a function of the island's size in the range of 100 to 100 000 atoms . The diffusion coefficient and the island evaporation rate exhibit a power law scaling of the island size. We find crossover behavior in the scaling exponents between the regime of intermediate sized islands (between 100 and 1000 atoms) and large islands (greater than 1000 atoms). At high coverages , we also examine these quantities for vacancy islands. We find that interm ediate island sizes exhibit unusual scaling behavior. (C) 1999 American Ins titute of Physics. [S0021-9606(99)70330-2].