Investigating crystal microstructure of niobium materials by an x-ray diffraction reciprocal space mapping technique

Abstract

An x-ray diffraction reciprocal spacing mapping (RSM) technique was applied to investigate crystal quality of Nb films and bulk materials, relevant to superconducting radio frequency applications. The RSM study used different x-ray penetration depths to study material processes after two different surface treatments: mechanical polishing or energetic condensation (a plasma process). The study revealed the material’s microstructure evolution for the two different processes. The RSM plots revealed crystal quality of the materials at different thickness. The novel, differential-depth RSM technique presented in this study substantiated the following facts: (1) For a heteroepitaxial Nb film Nb(100)/MgO(100), a film thickening process, via a cathodic arc-discharge Nb ion deposition (energetic condensation), created a near-perfect single crystal Nb on the surface top layer. (2) For a fine mechanically polished single-crystal bulk Nb material, the microstructure on the top surface layer is more disordered than that at a greater depth.