An exceptionally high barrier (0.35eV) for surface self-diffusion, and a negative additional energy (-0.053eV) for step-down diffusion, were measured for Pd on Pd(111). Both figures agreed with the proposed role of free-electron like surface states. In spite of the above negative value, layer-by-layer growth was not observed, and this was attributed to the low pre-exponential factor for step-down diffusion. Pre-adsorption of O increased the energy for step-down diffusion, but flattened the films. This again was attributed to the pre-factor for diffusion. These results demonstrated the importance of entropic effects in diffusion and growth.

Energetic and Entropic Contributions to Surface Diffusion and Epitaxial Growth. A.Steltenpohl, N.Memmell: Physical Review Letters, 2000, 84[8], 1728-31