An atomistic simulation study of a solid monolayer and trilayer of n-hexane on graphite

We present all-atom molecular dynamics simulations of n-hexane on the basal plane of graphite at monolayer and trilayer coverages. In keeping with experimental data, we find the presence of ordered adsorbed layers at both coverages. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate lattice to a fully commensurate structure on increasing the coverage from a monolayer to a trilayer. The zig-zag backbone planes of all the alkane molecules lie parallel to the graphite surface at the trilayer coverage, while a few molecules are observed to attain the perpendicular orientation at monolayer coverage