Kinetics of island diffusion on Cu(111) and Ag(111) studied with variable-temperature STM

The diffusion of vacancy islands on Cu(111) and Ag(111) and of adatom islan ds on Ag(lll) has been studied using fast scanning STM. Diffusion of atoms along island edges (periphery diffusion) is much more effective in contribu ting to the diffusion of the islands than diffusion of atoms via terrace si tes, under the conditions considered in this work. Assuming power-law scali ng of the diffusion coefficient with the size of the islands, effective exp onents, beta, between 1.33 and 1.63 were determined. The effective diffusio n barrier E-d was found to be 0.49 eV on Cu and between 0.51 and 0.53 eV on Ag, respectively. Activation energies for the diffusion of atoms along the island edges and for the breaking up of closed island edges (core breakup) were calculated using potentials derived from effective medium theory. Qua litative and quantitative comparisons between the measured and calculated a ctivation energies for diffusion show that one cannot explain the island di ffusion as being governed by one single rate-limiting process. The results are consistent with a mechanism for which both periphery diffusion and core breakup are rate-limiting for island diffusion. (C) 2000 Elsevier Science B.V. All rights reserved.