SELF-DIFFUSION OF ADATOMS ON FCC(110) SURFACES

We investigate the mechanisms and associated energies of diffusion for the Ni/Ni(110), Cu/Cu(110), Pd/Pd(110) and Ag/Ag(110) systems using the corrected effective medium (CEM) method. On the (110) surface, cross-channel diffusion can occur via atomic exchange of the adsorbate atom with an atom of the channel wall or by hopping over the short-bridge site located in the channel wall. We find that the barrier for cross-channel diffusion is much smaller for the atomic exchange path. In-channel diffusion occurs via hopping over the long-bridge site. We find that the activation barrier associated with in-channel diffusion is smaller than the activation barrier associated with cross-channel diffusion by 0.17, 0.01, 0.03 and 0.08 eV for Ni, Cu, Pd and Ag, respectively. We also investigate convergence of the activation barriers by varying the number of active atoms in the simulations. Decreases of 0.3-0.6 eV are found as the number of active atoms is increased from nearest neighbors to a (converged) large number of active atoms; this is due to relaxation of the strain. The decreases are nearly identical for the in-channel and cross-channel mechanisms.