Surface electromigration and self-diffusion on gold films studied via scanning tunneling microscopy

The evolution of monolayer islands, voids and terraces on the surface of polycrystalline gold films due to atomic self-diffusion and upon current stressing (electromigration) is studied using scanning tunneling microscopy. At room temperature with no current stressing, isolated islands and voids shrink, while in regions having high step density the area of terraces remain nearly constant, suggesting that surface dynamics is dominated by atom diffusion along the terraces. In contrast, when current is driven through the film, we occasionally find enlargement of voids and islands. In addition, we observe migration of steps leading to variations of terrace areas and, in some cases, to step bunching, indicating a significant contribution from atoms hopping over steps. Our data on the evolution of monolayer islands and atomic steps also provide information on activation energies for detachment from steps.