Molecular dynamics simulations for the Ag/Cu (111) system: from segregatedto constitutive interfacial vacancies

The occurrence of an Ag layer on top of a Cu (111) substrate can result fro m either deposition (Ag/Cu) or strong segregation at the surface of a dilut e Cu(Ag) alloy. Molecular dynamics simulations within many-body tight-bindi ng potentials show that two structures compete: one corresponding to a rath er uniform Ag (111) layer on top of a Cu (111) substrate leading to a Moire structure and the other involving constitutive vacancies forming triangula r loops of partial dislocations in the first Cu substrate layer. A useful g uide 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 depos it over a Cu (111) substrate. (C) 2000 Elsevier Science B.V. All rights res erved.