Electrodeposition of Ag, Pd and Au on Ni monolayer islands on (1 × 1)-Au(111) by in-situ scanning tunneling microscopy

We study the initial stage of the electrodeposition of Ag, Pd and Au on Ni submonolayers deposited on unreconstructed Au(111) by in-situ scanning tunneling microscopy. At submonolayer coverage all the deposited Ag forms islands on the Au substrate. Ag partially wets the Ni island edges but does not nucleate on top of the Ni islands. On the other hand, we found a completely different behavior for Pd and Au which nucleate on top of the Ni islands, undergo place exchange with the Ni atoms and also form rims wetting the entire Ni island edges. By selectively dissolving the Ni, we evidence an unexpected behavior: the initial stage of Pd place exchange occurs at the minima of the Ni moiré whereas it occurs at the maxima in the case of Au. The origin of the difference between Pd and Au preferential place exchange site is attributed to the presence of a hydrogen overlayer.