Developing a Chemical and Structural Understanding of the Surface Oxide in a Niobium Superconducting Qubit

Akshay A. Murthy*, Paul Masih Das, Stephanie M. Ribet, Cameron Kopas, Jaeyel Lee, Matthew J. Reagor, Lin Zhou, Matthew J. Kramer, Mark C. Hersam, Mattia Checchin, Anna Grassellino, Roberto Dos Reis, Vinayak P. Dravid, Alexander Romanenko

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Superconducting thin films of niobium have been extensively employed in transmon qubit architectures. Although these architectures have demonstrated improvements in recent years, further improvements in performance through materials engineering will aid in large-scale deployment. Here, we use information retrieved from secondary ion mass spectrometry and electron microscopy to conduct a detailed assessment of the surface oxide that forms in ambient conditions for transmon test qubit devices patterned from a niobium film. We observe that this oxide exhibits a varying stoichiometry with NbO and NbO2found closer to the niobium film/oxide interface and Nb2O5found closer to the surface. In terms of structural analysis, we find that the Nb2O5region is semicrystalline in nature and exhibits randomly oriented grains on the order of 1-3 nm corresponding to monoclinic N-Nb2O5that are dispersed throughout an amorphous matrix. Using fluctuation electron microscopy, we are able to map the relative crystallinity in the Nb2O5region with nanometer spatial resolution. Through this correlative method, we observe that the highly disordered regions are more likely to contain oxygen vacancies and exhibit weaker bonds between the niobium and oxygen atoms. Based on these findings, we expect that oxygen vacancies likely serve as a decoherence mechanism in quantum systems.

Original languageEnglish (US)
Pages (from-to)17257-17262
Number of pages6
JournalACS nano
Issue number10
StatePublished - Oct 25 2022


  • 4D-STEM
  • Nb thin films
  • decoherence mechanisms
  • electron diffraction
  • hydrides
  • interfaces
  • superconducting qubits

ASJC Scopus subject areas

  • General Engineering
  • General Physics and Astronomy
  • General Materials Science


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