A Monte Carlo study of surface segregation in alloys

The Monte Carlo method has been applied to the study of surface segregation in a multi-layer, regular solution model of alloy surfaces. Three different alloy configurations have been investigated: semi-infinite slabs, thin films and small particles. The results show that the alloy component with the lowest surface energy tends to segregate to the first three or four surface atom layers and that segregation is greater in clustering alloys than in ordering alloys. Furthermore, segregation is more pronounced in low coordination surfaces, as evidenced by a comparison of {110} and {100}-oriented surfaces of fcc alloys. The degree of surface segregation in thin films and small particles (in the particle size range studied) tends to be smaller than in semi-infinite slabs, because of mass conservation constraints, and decreases with decreasing film thickness and particle size. The results obtained are contrasted with previous calculations and possible avenues for improving surface segregation models are discussed.