Strain and dislocation blocking in Ni/Cu superlattices

Abstract

In this work we investigate the strain state in Ni films belonging to [Ni(tNi)/Cu(tCu)] × N superlattices (with tNi = 2 nm, 3 nm, tCu from 0 to 3 nm and N between 1 and 6) by Extended X-ray Absorption Fine Structure at the Ni K-edge. The strain of these Ni blocks can be up to 80% larger than that obtained for single thin films with the same content of Ni. The dependence of the strain on N indicates that its relaxation is not progressive with N but gets blocked for certain N values. Also, the replacement of a single Ni layer by Cu, at the middle of the Ni block, results in a significant increment of the strain of the nickel layers, which manifests the relevant effect of the introduction of copper. The large strain values observed suggest the presence of blocking mechanisms acting on the propagation of dislocations. We argue that this observation is related to repulsive interactions between dislocations enhanced by nonhomogeneos stress due to presence of the copper layers separating the Ni blocks.