An embedded atom analysis of Au clusters on a Ni surface

Abstract

The embedded atom model (EAM) was utilized to analyze the cohesive energy and atom positions of Au clusters on a (111) Ni surface. The cohesive energy per atom of Au in the clusters decreased as the cluster size increased, and the cohesive energy per atom in large monolayer clusters was less than the bulk chemical potential indicating that monolayer clusters were favored over three-dimensional clusters. For all monolayer and three-dimensional clusters analyzed, the monolayer was of lower energy for the same number of Au atoms. Small Au clusters (less than 17 atoms) were calculated to have the bulk lattice parameter or to be in a slight state of compression and to assume a “tent” type shape with the center atom pushed away from the Ni substrate. For larger Au clusters the outer atoms in the cluster passed over saddle points between Ni atoms on the (111) surface and occupied positions that created stacking faults in the cluster; also, the Au cluster was significantly strained in tension after the Au atoms at the edge of the cluster passed the Ni saddle-point positions. The Ni substrate surface was significantly strained in tension particularly for large Au cluster sizes. Au atoms on the outer edge of large clusters were displaced into the substrate and Ni surface atoms outside the cluster were displaced out of the surface; this could provide an effective mechanism for blocking cluster mobility.