Phase diagram and phase transitions of the adsorbate system S/Ru(0001): a Monte Carlo study of a lattice gas model

Abstract

We investigate the phase diagram and the critical properties of the adsorbate system sulphur/ruthenium(0001) in the coverage region 0 < Θ < 1/3 using Monte Carlo simulations of a lattice gas model on a triangular lattice. From experiments it is known that for low coverages an island phase appears in the phase diagram of this system at low temperatures. To capture this feature we include in our lattice gas model a weak third neighbour attraction in addition to the repulsive first and second neighbour forces. The phase diagram obtained from simulations of this model is in very good agreement with the experimental phase diagram. The critical properties of the lattice gas model are found to be compatible with the results of experiments on the system sulphur/ruthenium(0001). Finer details of the phase diagram, e. g. the location of tricritical points, which may be difficult to assess experimentally will also be discussed.