Ag/Cu(111) structure revisited through an extended mechanism for stress relaxation

The Ag/Cu(111) system can be considered as a model one concerning the atomic structure of one monolayer deposited on a substrate in the case of strong size mismatch. Thus, it has been the subject of many experimental [Auger electron spectroscopy, low-energy electron diffraction and scanning tunneling microscopy (STM)] and theoretical studies, in particular within N-body potentials. Although most results agreed both with the existence of an n x n superstructure accommodating the size mismatch and with a strong corrugation of the Ag adlayer, the morphologies-derived from STM on the one hand and numerical simulations on the other hand-were not found to be consistent. Here we revisit the previous theoretical study, taking into account different additional mechanisms (Ag and Cu vacancy formation, partial dislocation loop) to relax the interfacial stress. As a result, we obtain that the most efficient relaxation mechanism is the formation of partial dislocation loops in the first Cu substrate layer, requiring the formation of four or five Cu vacancies per unit cell in this plane. This lends to a strong damping of the corrugation in the Cu underlayers, and a perfect agreement is reached between observed and calculated surface morphology. [S0163-1829(99)14915-4].