Metal adsorption and adhesion energies on MgO(100).
The calormetically measured heats of adsorption of Cu, Ag, and Pb on MgO(100), previously measured in our group, are correlated with bulk properties of the metals and their sticking probabilities and film morphologies. The low-coverage heats of adsorption (when the metals are mainly in two-dimensional (2D) islands) are used to estimate metal-MgO(100) bond energies within a pairwise bond additivity model. These values correlate well with the observed initial sticking probabilities and saturation island densities of the metals. This supports a transient mobile precursor model for adsorption. The values also correlate with their bulk sublimation energies, which suggests that covalent metal-Mg bonding dominates the interaction at low coverage, probably due to very strong bonding at defects. The heats of adsorption integrated up to multilayer coverages provide the metal-MgO(100) adhesion energies and metal-MgO(100) bond energies for metals in 3D films. These values correlate with the sum of magnitudes of the metal's bulk sublimation energy plus the heat of formation of the bulk oxide of the metal per mole of metal atoms. This suggests that local chemical bonds, both metal-oxygen and covalent metal-Mg, dominate the interfacial bonding for 3D films.
Campbell
Charles T
CT
Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195-1700, USA. campbell@chem.washington.edu
Starr
David E
DE