Ordering transition of gases adsorbed on a C₆₀ surface: Monte Carlo simulations and lattice-gas models

A monolayer of C60 molecules on a flat surface provides an unusual substrate for the adsorption of simple gases. Both the lattice constant and the corrugation are larger than is typical of most traditional surfaces. These differences give rise to different phenomena, such as unusual commensurate phases. This paper discusses the ordering transition of various gases corresponding to the filling of the honeycomb array of threefold coordinated hollow sites located between C60 molecules. That transition is investigated with Monte Carlo simulations and analytical (lattice-gas) models. The value of the resulting transition temperature (Tc) depends on the form assumed for the long-range interaction and the role of many-body effects, i.e., screening, due to gas molecules' close proximity to the C60 layer. The effect of three-body interactions is found to be large in all cases considered.