Ionic monolayers on metals: I. layers of like ions

We estimate the energy of a layer of like ions adsorbed on an atomically smooth face of a metal crystal. We consider only adions of large radius, so that the method of electrostatic images can be used in evaluating the energy. For periodic layers of high density, we find large deviations from the dipole approximation of Topping. Also, we estimate the increase in electrostatic energy accompanying disordering of a layer, and use the result to discuss thermal disordering of Na and Cs layers on W(110). We emphasize that the charge transfer to a layer of like ions must be small. For example, O and S anions of integral charge cannot form densely packed layers on metals.