Glancing-incidence X-ray characterization of Nb/Pd multilayers

The study of periodic metallic multilayers in which one of the two constituent layers is a superconductor has attracted considerable interest. The structural configuration and quality of the interfaces is of fundamental importance because it influences the phases of the superconductive wave function in the interface region and, hence, the coupling between the nearest superconductive layers. In this work we present a structural investigation of Nb/Pd multilayers by using high- and low-angle X-ray diffraction measurements. All the samples were grown on Si(100) substrates by de-triode sputtering. We investigated two samples consisting of 10 stacks of nominally 19 nm Nb, 4 nm Pd and 18 nm Nb, 8 nm Pd, respectively. The high-angle analyses reveal that the Nb layer is oriented in the [110] direction and the Pd in the [111] direction. Off-specular reflectivity measurements show the presence of a (partially) correlated roughness across the interfaces. From specular reflectivity it was found how the rms roughness increases from the substrate to the surface.