Size effects in surface segregation

The effect of the slab thickness (d) on the segregation behavior has been investigated for a phase separating system in a slab consisting of atomic planes parallel to the free surfaces. The calculations were carried out using the Fowler-Guggenheim approximation in the monolayer limit. It is shown, that by varying the surface fraction xi, a surface phase transition can occur, similar to a semi-infinite system where a change in temperature can lead to a phase transition (S-shaped segregation isotherm). Furthermore, the existence of a minimum on the free energy curve versus d was examined. It was demonstrated that such a minimum can exist in the nanocrystalline region. (C) 1998 American Institute of Physics.