Surface segregation in ternary alloys: a BFS study of Ni-Al-Cu(100) surface composition

Atomistic simulations of surface segregation constitute an essential tool i n determining the surface composition and structure of binary or higher ord er alloys. The presence of metastable stares, where widely different surfac e composition profiles are energetically possible, are severe tests for the ability of experimental techniques for accurately determining the composit ion of the surface. A clear example of such phenomenon is analyzed in this paper, where the Bozzolo-Fenante-Smith (BFS) semiempirical method for alloy s is applied to the study of surface composition of Ni-rich Ni-Al-Cu alloys . A wide range of Cu concentration is considered, showing distinct segregat ion trends characterizing the low-Cu and high-Cu concentration regimes. The existence of metastable states with energy close to that of the ground sta te is identified and shown to drive the resulting segregation pattern. The results of several Monte Carlo/Metropolis simulations are shown, highlighti ng the role of the initial state used in the simulation and the temperature treatment of the sample. (C) 1999 Elsevier Science B.V. All rights reserve d.