Monte Carlo simulation of Cu segregation and ordering at the (110) surfaceof Cu75Pd25

The segregation to the (110) surface of a Cu75Pd25 single crystal is modell ed as a function of temperature by Monte Carlo simulations combined with th e embedded atom method (EAM). Using EAM parameters from literature, optimis ed for the six transition metals of the Cu and Ni groups, does not yield sa tisfactory results: too low a bulk order disorder transition temperature T- c and, contrary to experimental evidence, Pd surface segregation and a diso rdered surface layer are obtained. These observations are contradicted by t he LEIS results of Bergmans et al. [Surf. Sci. 345 (1996) 303] that reveale d an ordered bulk with an oscillating concentration profile at least up to 600 K and a Cu-enriched surfacer They also observed a (2 x 1)LEED pattern c aused by ordering in the second layer. In this work the EAM parameters are recalculated and optimised precisely for the Cu Pd alloy system under study . The results of the simulations are now in perfect agreement with the expe rimental findings: a bulk critical order-disorder temperature in agreement with the bulk Cu- Pd phase diagram, an oscillating concentration profile. C u segregation to the surface and a second atomic layer exhibiting a substan tial degree of ordering that accounts for the observed (2 x 1) LEED pattern . (C) 1998 Elsevier Science B.V. All rights reserved.