Molecular dynamics simulations for the AgrCu 111/ system: from segregated to constitutive interfacial vacancies

The occurrence of an Ag layer on top of a Cu 111.substrate can result from either deposition AgrCu.or strong segregation at the surface of a dilute Cu Ag. alloy. Molecular dynamics simulations within many-body tight-binding potentials show that two structures compete: one corresponding to a rather uniform Ag 111.layer on top of a Cu 111. substrate leading to a Moire´ structure and the other involving constitutive vacancies forming triangular loops of partial dislocations in the first Cu substrate layer. A useful guide to predict the most efficient relaxation mechanism is to characterize the regions which undergo the largest stress. Thus, the local pressure map in the first Cu underlayer allows to predict a complementarity between the segregation of vacancies in compressive sites and the Ag enrichment, due to the larger atomic radius of the Ag atoms, in the tensile ones. Segregation energy maps, both for vacancies and Ag atoms, confirm this prediction and lead to several perspectives for the kinetics of dissolution of an Ag deposit over a Cu 111. substrate. q2000 Elsevier Science B.V. All rights reserved