Surface-induced ordering in phase separation systems: influence of concentration and orientation

With regard to the modern way of analysing surface phenomena at an atomisti c scale, new questions appear. This is particularly the case with the tende ncy to either order or phase separate, for which experiments reveal a possi ble reversal from the bulk to the surface. Our aim in this paper is to show , through a microscopic theoretical model derived from the tight-binding sc heme, that such a behaviour can be understood. We are thus able to predict how the tendency to form heteroatomic or homoatomic pairs evolves with the number of broken bonds (surface orientation) and the alloy concentration (a t least in the dilute limits). This is illustrated in the case of the Ag-Cu system, which presents a strong phase separation in the bulk and for which many experiments reveal a large variety of surface behaviours. (C) 1999 El sevier Science B.V. All rights reserved.