Thermodynamics of binary alloy thin films

The thermodynamics of ordering binary alloy thin films with non-neutral or ‘polarizing’ boundary conditions is studied within the frame of an Ising-like Hamiltonian with nearest-neighbor interactions. The finite-temperature behavior is obtained by means of the pair approximation of the cluster variation method which is the lowest approximation that takes into account short-range correlations. The analysis focuses on the dependence upon film thickness of the phase diagrams and on the nature of the surface field (Δ) which acts close to the surface and leads to segregation of one of the components. The finite-size and surface effects along with the discreetness of the system entail novel features on the phase diagrams that are not present in continuous theories and/or in the usual mean-field theory (Bragg-Williams) that neglects short-range order correlations. Temperature-chemical potential and temperature-concentration phase diagrams are presented as well as concentration and long-range order profiles.