Kinetic Monte Carlo simulation of surface segregation in Pd-Cu alloys

The knowledge of surface composition and atomic arrangement is prerequisite for understanding of catalytic properties of an alloy catalyst. Gaining such knowledge is rather difficult, especially for those possessing surface segregation. Pd-Cu alloy is used in many fields and possesses surface segregation. In this paper kinetic Monte Carlo method is used to explore the surface composition and structure and to examine the effects of bulk composition and temperature on the surface segregation of Pd-Cu alloys. It is shown that the segregation basically completes within 900 s at 500 K. Below 900 K and within 20 min the enriched surface Cu atoms mainly come from the top five layers. For the first time we demonstrate that there exists a bulk-inside flocking or clustering phenomenon (the same component element congregates in bulk) in Pd-Cu alloys. Our results indicate that for alloys with higher Cu content there are small Pd ensembles like monomers, dimers and trimers with contiguous subsurface Pd atoms. (C) 2015 Elsevier B.V. All rights reserved.