Structural Analysis for the Oxide Surface of Nb(110) with Atomic Force Microscopy

Nb has the highest superconducting transition temperature among elemental materials, which makes it a realistic choice for superconducting junctions. However, self-organized oxide structures on its surface impede the preparation of well-defined interface. Once the oxide structure is clarified, this oxidized surface may be used as an interface. Atomic force microscopy can distinguish different elements among ionic crystals depending on the charge state of the scanning probes. We applied this method to the oxide surfaces of Nb(110) for structural analysis and observed Nb and O atoms independently as well as simultaneously. A structural model was constructed based on the density functional theory. Additionally, the density of states and the Bader charge were analyzed.