Electrodeposition of NiPd monolayer on Au(1 1 1): An in situ scanning tunneling microscopy study

We investigate the morphology of the first monolayer of NiPd alloys electrodeposited on Au(1 1 1) by in situ scanning tunneling microscopy. The detailed analysis of the average height of the alloy monolayer and the in-plane distribution of its corrugation maxima suggest a microstructural transition at around 30% Pd content. Below 30% Pd content, the NiPd monolayer is a solid solution while phase separation occurs at the nanometer scale above this value. A simple thermodynamic model is presented, which shows that this structural transition may be accounted for by considering the balance between the interface energies and the configuration entropies of the alloy and the Ni and Pd pure phases.