Modeling image potential surface states on silver and gold surfaces covered with self-assembled monolayers of alkanethiols and alkaneselenols

A one-dimensional potential based on nearly free electron (NFE) theory and the method of images is used to describe image potential surfaces states on roughened Ag and Au surfaces covered with self-assembled monolayers of alkanethiols and alkaneselenols. NFE is applied to produce the model potential in both the substrate and headgroup portion of the monolayer, and calculated image state energies are in excellent quantitative agreement with experimental energies. The image plane is located beyond the headgroup layer that is chemisorbed onto step edges, and the electrons move perpendicular to step edges and parallel to terraces.