First-principles investigation of the early stages of Pd adsorption on Au(111)

We present the results of density functional theory simulations of the adsorption of Pd on the Au(111) surface at low coverage. The potential energy surface for Pd adatoms is determined and found to be shallower than that related to atomic-size features observed in scanning tunneling experiments. The commonly found Pd–Pd repulsion within Au also applies in the case of adatoms on a perfect Au(111) surface interacting with surface/subsurface ones, despite the role of the latter entities in the island nucleation on the real, reconstructed surface. Alteration of the surface lattice parameter or of the stacking of Au layers, featured by the Au(111)-(22\times \sqrt {3}) surface, is also modeled and found not to modify the energetics of Pd islands. The appearance of Pd monomers in simulated scanning tunneling topographies is discussed and shows an important contribution by the Au surface state in determining the relative height of surface and subsurface Pd atoms, in agreement with recent experimental findings.