THERMODYNAMICS OF BINARY ALLOY THIN-FILMS

The thermodynamics of ordering binary alloy thin films with non-neutra l or 'polarizing' boundary conditions is studied within the frame of a n Ising-like Hamiltonian with nearest-neighbor interactions. The finit e-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 na ture of the surface field (Delta) which acts close to the surface and leads to segregation of one of the components. The finite-size and sur face effects along with the discreetness of the system entail novel fe atures on the phase diagrams that are not present in continuous theori es and/or in the usual mean-field theory (Bragg-Williams) that neglect s short-range order correlations, Temperature-chemical potential and t emperature-concentration phase diagrams are presented as well as conce ntration and long-range order profiles.