Step-controlled ultra-precise chemical etching for removing chemical residues from metallic niobium surfaces

This work presents a highly precise chemical etching process designed to achieve controlled modulation of the formation and removal of the oxide layer on the surface of niobium (Nb). Angle-resolved X-ray photoelectron spectroscopy (ARXPS) results indicate that the surface attains a saturated oxide layer thickness above 3 nm following treatment with HNO₃. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results show that the removal efficiency of chemical residue on the Nb surface significantly improves with increased treatment time in HNO₃ and HF. A detailed surface analysis with a 3D optical profiler demonstrates that this method enables uniform etching without compromising the surface flatness of Nb while effectively removing the chemical residues. Electrochemical stability measurements and Vickers hardness tests reveal that cyclic etching exerts minimal impact on the mechanical properties of Nb, while the self-healing characteristics of the surface oxide layer maintain its chemical stability. This method not only advances precision etching for Nb but also opens up the potential for its application in high-performance materials where surface integrity and chemical resilience are paramount.