Effect of impurities on surface stress on an atomic scale

Abstract

Atomic-scale calculations of stress induced by a transition metal adsorbate on a metal surface are presented. A newly developed many-body potential is used. We show that Co adatoms strongly reduce local surface stress and lead to an inhomogeneous stress distribution. Barriers of jump and exchange diffusion are determined for Co on Au~001!. We predict that the exchange process is energetically favorable. Molecular dynamics calculations are performed to determine the coverage dependence of the adsorbate-induced surface stress. While the concept of surface stress was introduced by Gibbs at the beginning of the 19th century, 1 the importance of surface stress has become widely appreciated only in the last 10 years. 2 Results of many investigations demonstrated a strong impact of stress on surface diffusion, 3 surface reconstruction 4 and surface morphology. 5 One can consider surface stress as a new parameter in experimental and theoretical investigations on surface growth modes and physical properties of nanostructures. 6 To our knowledge, it is not yet possible to measure stress directly. In all experiments only changes in stress, caused by adsorbates or reconstruction, were determined. Therefore, theoretical studies of surface stress, both ab initio and semiempirical, are of a great importance. First-principle calculations of surface stress for several clean metals were performed by Needs et al. 7 They found that the kinetic energy of electrons introduce the largest contribution to stress. Ab initio studies of Fiorentini et al. 8 showed that the reconstruction of the late 5 d metals is related to the large tensile stress on these surfaces. Semiempirical calculations of surface stress of various metals were performed by means of the embedded atom method and Finnis-Sinclair potentials. 9 Several ab initio and semiempirical studies on surface stress in semiconductors were reported. 10