Comparison between different X-ray diffraction methods to extract strains in metallic multilayers

It is well known that, in multilayers, the information on perpendicular lattice strains is hidden in the intensity of the superlattice peaks, whereas the positions of the diffraction lines are related to the superperoid. This calls for some refinement. A standard way to extract stresses in a variety of materials is to perform a “Sin2 ψ analysis” (ψ is the angle between the lattice planenormal and the sample surface normal). This method relies on the measurement of asymmetric Bragg peakswhich may contain superlattice reflections. On the other hand, the in-plane directions, as measured by X-ray diffraction in the grazing incidence or the transmission modes, do not involve any superstructure; thus they can lead straightforwardly to in-plane distances. A detailed comparison between the Sin2 ψ technique,i.e. lattice strain measurements from asymmetric Bragg peaks, and the e⊥/e‖ method will be presented. This study is performed on Au−Ni multilayers. One of the major conclusions is that the Sin2 ψ analysis is always valid but the measurement of lattice strain becomes more complicated when the layers are epitaxial.