Atomic-scale Investigation of the Nb/air Interface for Niobium Radio Frequency Cavity

Niobium radiofrequency cavities hold great promise to realize quantum computation, while the coherence time loss of quantum bit (qubit) by surface resistance, in particular oxides, impairs the system's lifetime. We present a comprehensive structural and chemistry study of the Nb/air interface from a niobium cavity using aberration-corrected transmission electron microscopy (TEM) and spectroscopy techniques. The results directly prove that the oxidation process is oxygen diffusion-controlled, and the NbOx/Nb interface is related to the crystallographic orientation of the Nb metal. Moreover, we will discuss different surface protection methods during focus ion beam TEM sample preparation on the Nb oxide layer structure.