Investigating oxidation in superconducting bilayers using X-ray photoelectron spectroscopy

The formation and propagation of surface oxides in superconducting thin films are known to be a significant source of loss in superconducting resonators and qubits. Thus, there have been several studies attempting to understand both the mechanisms and mitigation of such oxides. One approach to the mitigation of surface oxide is the addition of a second layer which acts as an oxygen diffusion barrier. Here, we demonstrate our use of X-ray photoelectron spectroscopy (XPS) as a tool for rapid characterization of various metals as effective oxygen diffusion barriers for niobium. We evaluate various bilayers based on oxide formation at the niobium-metal interface in unannealed and annealed conditions. The use of the XPS enables a rapid turn-around and assessment of barrier metals for further device fabrication and microwave characterization. We also show applications of XPS in the assessments of resonator and general fabrication processes.