Surface coupling effect on wetting and layering transitions

The effect of the surface coupling J(S) on the dependency of the layering transition temperature T-L as a function of the thickness N, of a spin-1/2 Ising film, is studied using the mean field theory. It is found that for J(s) greater than a critical value (J(sc) = 1.30), the layering transition temperature decreases when the film thickness N increases for any values of the surface magnetic field H-s. While, for J(s) < J(sc), the behaviour of the layering transition temperature T-L, as a function of N, depends strongly on the values of H,. Indeed, we show the existence of three distinct behaviours of TL, as a function of the film thickness N, separated by two critical surface magnetic fields H-sc1 and H-sc2, namely: (i) for H-s < H-scl, T-L increases with N; (ii) for H-scl < H-s < H-sc2, T-L increases for small values of N, and decreases for large value ones; (iii) while for H-s > H-sc2, T-L decreases with increasing the film thickness. Furthermore, depending on the values of J(s), the wetting temperature T-w (T-w = T-L when N --> infinity for a given material), can be greater or smaller than the layering transition temperature of a film of thickness N of the same material. (C) 2003 Elsevier Science B.V. All rights reserved.