Investigation of profile characteristics and interface of anodized niobium superconducting films

• Microstructure evolution of anodized Nb films.
• An amorphous NbOx layer in the interface between Nb layer and Nb2O5 layer.
• It is suggested that the anodization process mechanism of Nb films may start from NbOx, and subsequently developing to Nb2O5.
• The rate of consumed Nb and produced Nb-oxide layer was measured for our anodization process.

The profile and interface characteristics of anodized Nb (Nb-oxide) layer were investigated using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The surface morphology of Nb-oxide layer shows smoother as well as the Nb grain gradually vanished with increasing anodization depth. The root mean square (RMS) roughness of Nb-oxide layer was decreased to be 0.35 nm with increasing applied voltage of anodization to 100 V. An amorphous NbOx layer in the interface between Nb layer and Nb2O5 layer was confirmed by X-ray reflectometry (XRR) and transmission electron microscopy (TEM) analysis. The thickness of NbOx layer decreases to be 1.5 nm with the increasing anodization depth for 45 nm depth Nb-oxide layers, which is comparable to the value observed on the surface of Nb films.