A study was made of the adsorption-induced surface reconstruction phenomenon by using the so-called four-position model for the H2/W(001) system. In the framework of the lattice-gas scheme, the model contained 4 equilibrium positions for the W surface atom and the adsorption sites were located between them. Adsorption-induced reconstruction phenomenon occurred when the surface metal atoms structure goes through a second-order phase transition from a c(2 x 2) order to disorder. The ground-state map was calculated and, as a result, 3 possible fundamental structures emerged for both metal and adsorbed atoms. By Monte Carlo simulations and finite-size scaling analysis, the critical temperature was calculated and consequently the phase diagram for the surface metal structure as well as for the adsorbed atoms. A novel result was that it was observed, in the framework of this model, that a reconstruction transition was possible only if the adsorbed layer presented a (2 x 1) ordered phase. Other adsorbate structures, such as a c(2 x 2) phase, did not affect the critical behaviour of the surface metal atoms arrangement, however, it was shown that the phase diagram for the adsorbed phase was strongly modified by the surface metal atoms structure.

A Model for Adsorption-Induced Surface Reconstruction - Ground-State and Phase Diagrams. F.Nieto, V.Pereyra: Surface Science, 1998, 399[1], 96-108