Synthesis and Characterization of Mo–Nb Films Superconducting at 100–200 mK

We have developed a new transition-edge sensor material with critical temperature ( T c ) in the range 100–200 mK. The new material is a solid solution of two superconducting components, Mo x Nb 1− x , co-sputtered from two high-purity single-component targets (Mo and Nb). The T c has a minimum (d T c / d x = 0) at an intermediate concentration of the components. We have optimized the deposition parameters and composition to provide films with a sharp superconducting transition at ~ 150 mK. We investigated structural features of the films and surface morphology using X-ray diffraction (XRD) and scanning electron microscopy. The XRD measurements indicate that the grown films are polycrystalline, with a preferred orientation along the (110) crystal direction and a clear correlation between superconducting properties and film microstructure.