Monte Carlo Simulations of Underpotential Deposition.

M. C. GIMÉNEZ; E. P. M. LEIVA

Monastery of Benediktbeuern (Germany)

Simposio; 11th International Fischer-Symposium on "Microscopy in Electrochemistry"; 2009

The adsorption of a metal monolayer or submonolayer for the systems Ag/Au(100), Au/Ag(100), Ag/Pt(100), Pt/Ag(100), Au/Pt(100), Pt/Au(100), Au/Pd(100) and Pd/Au(100) was studied by means of lattice Monte Carlo simulations. It was found that, taking into account some general trends, such systems can be classified into two big groups. The first one comprises Ag/Au(100), Ag/Pt(100), Au/Pt(100) and Au/Pd(100), which have favourable binding energies as compared with the homoepitaxial growth of adsorbate-type atoms. When the simulations are performed in the presence of substrate-type island in order to emulate surface defects, the islands remain almost unchanged, and the adsorbate atoms successively occupy kink sites, step sites and the complete monolayer. The second group is composed of Au/Ag(100), Pt/Ag(100), Pt/Au(100), and Pd/Au(100), for which monolayer adsorption is more favourable on substrates of the same nature than on the considered substrates. When simulations are carried out in the presence of islands of substrate-type atoms, these tend to disintegrate in order to form 2-D alloys with adsorbate atoms. On the other hand, a new model to study the efect of on top coadsorption of anions in underpotential deposition is formulated. It considers a lattice-gas model with pair potential interactions between nearest neighbors. As test system, the electrodeposition of silver on gold is studied by means of grand canonical Monte Carlo simulations. The influence of anions on the adsorption isotherms is analyzed. It is found that as the interaction between silver atoms and anions increases, the monolayer adsorbs at more negative chemical potentials. For large interactions between silver atoms and anions, a expanded structure occurs for the silver monolayer.