Electrochemical polishing of chemical vapor deposited niobium thin films

Combining chemical vapor deposition (CVD) with electrochemical polish (EP) operation is a promising route to producing performance-capable superconducting films for use in the fabrication of cost-effective components for superconducting radiofrequency (SRF) particle accelerators and superconducting quantum computers. The post-deposition EP process enables a critically necessary reduction in surface roughness of niobium (Nb) thin films to promote optimal superconducting surface conditions. This work investigated surface morphology, roughness, and crystal orientation of the CVD-grown and EP-polished Nb films. The CVD films were found to comprise steps and pyramidal features, resulting in undesirable large peak-to-valley distances. EP was demonstrated to significantly diminish the height of pyramids and effectively minimize the overall surface roughness. EP results showed a probable dependence on the crystal orientation. These understandings identify the EP principles tied to CVD-grown Nb films that allow further refinement of surface profiles for film-based SRF applications. •Chemical-vapor-deposited (CVD) niobium films show large steps and pyramidal features.•Electropolishing (EP) reduces large surface roughness on CVD niobium films.•EP of CVD niobium films involves both macroscale and microscale smoothing.•The film EP results suggest a probable crystal orientation dependence.•Combining EP-CVD makes film-niobium feasible for superconducting radiofrequency use.