A Study of the Adsorption of Monoatomic Adsorbate Adlayers on FCC and HCP Metals Using the Sphere-in-Contact Model

We have recently shown that the sphere-in-contact model can be used as an educational and research tool in various contexts, such as the visualization of carbon structures (e.g. graphene, carbon nanotubes, carbon nanocones and graphite), heterogeneous catalysts, metal nanoparticles and organic molecules. In this study we present how it can be used to model the adsorbate structure of a monoatomic elements on the hexagonal close-packed surface of HCP and FCC metals to study long range ordering phenomena of monoatomic adsorbates on metals. We have used atoms of varying radius and colour to represent the metal surface atoms and the adsorbate atoms. The study reveals that many surface configurations are possible for a fixed adsorbate coverage (θ) by the movement of the adsorbate atoms in response to surface adsorbate-adsorbate repulsions. The movement of the particles (e.g. particle diffusion) can be seen directly in the model and this is caused by the user intervention. This has great educational but also research value as one can directly see how the adsorbate atoms reorder on the surface of a metal. We calculate the repulsive interaction energy of adsorbates using the sphere-in-contact model and are able to identify which surface adsorbed configuration is the lowest energy one. We find that this model will be useful in the rational design of catalytic materials and materials coatings with new technological applications where long range ordering of surface adsorbates is essential.