Simulations of Oxygen Monolayer and Bilayer Systems
We present the results of a simulation using a physical model developed to study the equilibrium configurations of adsorbed oxygen on graphite. In the model, an atom-atom potential between the oxygen and graphite was used which depended on the lateral positions of the oxygen molecules as well as the distance above the surface. A cluster model is proposed to study the low density region, for which very little information is available. The nucleation of adsorbed rare gas films on a graphite basal plane has been studied experimentally and interpreted using a two-dimensional cluster model [1,2]. The cluster model used in this study is an extension of the work done by Pan et al.  by including lateral variations of the potential in the gas-surface interaction. Zero temperature minimum energy structures of two-dimensional oxygen clusters with the number of O2 molecules in the cluster, N, ranging from 1 to 16 molecules adsorbed on the graphite basal plane surface are determined. The energies and structures of adsorbed infinite monolayer films are also studied with the energy minimization method which involved a search for possible low temperature superlattices. The acceptability of the superlattices is tested by comparing the superlattice energy to the incommensurate overlayer energy. This calculation, which includes the lateral variations of the gas-surface potential, allows the determination of the orientational epitaxy of the O2 overlayer. Both the δ  and δ′  orientational epitaxy were found in these calculations. The ζ1  and ζ2  phases were also found in these calculations. Initial studies of adsorbed bilayer systems are also presented.
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