Differential heat of adsorption in the presence of an order–disorder phase transition

We studied the coverage dependence of the differential heat of adsorption in the presence of an order–disorder phase transition, by employing theoretical mean-field and quasi-chemical approaches and Monte Carlo simulation, in the framework of the lattice-gas model. For a square lattice, with repulsive interactions between the nearest-neighbor adatoms, Monte Carlo reveals the existence of singularities in the differential heat at critical coverages, which are not observed through the theoretical approaches. The differential heat of adsorption appears as a sensitive quantity to the phase transition, allowing a very accurate determination of the phase diagram.