Properties of argon adlayers deposited on graphite from Monte Carlo calculations

Properties of argon adlayers deposited on a graphite substrate are calculated using a high resolution Monte Carlo calculation. Nine different surface densities are examined ranging from very partial to slightly beyond a complete monolayer. At low densities the calculated specific heats show two peaks. One is very sharp and one is broad. The sharp peak is shown to signal on orientational transition of the adlayer, and the broad one signals melting. The melting curve is calculated and compared with experiments, as are the lattice parameters at various temperatures. It is shown that second layer promotion plays an important role in the behavior of adlayers at some densities and temperatures. The orientational angle of the adlayer, with respect to the sublattice, is determined at various temperatures, and it is argued that the rotational transition is due to the relaxation of stress on the adlayer. It is found that the rotational transition disappears when the surface density increases beyond about 84% of that of a complete monolayer. This is in accord with experimental evidence. In order to identify and characterize the features of adlayers, various order parameters and probability distributions are calculated.