Mechanisms of atomic diffusion on the flat, stepped, and faceted surfaces of Al(110)

Using first-principles calculations based on density-functional theory, we elucidate mechanisms and energy barriers for atomic diffusion on Al(110), Al(100), and Al(111), up and down (100) and (111) steps on Al(110), and between the (100), (111), and (110) facets of Al. We find that the energetically preferred mechanism for adatom diffusion on Al(110) is a diagonal exchange between the adatom and the substrate, which leads to isotropic diffusion on this anisotropic surface. Similarly, diagonal exchange involving three atoms is the preferred mechanism for atoms to ascend and descend the (100) and (111) steps. The descent of atoms over the (100) steps is hindered by diffusion to the step edge while for the (111) steps, it is hindered by diffusion over the edge. Energy barriers to ascend from (110) to (100) or (111) facets depend on facet height. Neighboring adatoms can significantly influence diffusion-energy barriers and simple approaches cannot predict this complex behavior. The energy barriers for dimers to climb from the (110) to the (100) and (111) facets are lower than those for isolated adatoms.