Surface oxides, carbides, and impurities on RF superconducting Nb and Nb3Sn: a comprehensive analysis

Zeming Sun; Zhaslan Baraissov; Catherine A. Dukes; Darrah K. Dare; Thomas Oseroff; Michael O. Thompson; David A. Muller; Matthias U. Liepe

doi:10.1088/1361-6668/acff23

Surface oxides, carbides, and impurities on RF superconducting Nb and Nb₃Sn: a comprehensive analysis

Zeming Sun, Zhaslan Baraissov, Catherine A. Dukes, Darrah K. Dare, Thomas Oseroff, Michael O. Thompson, David A. Muller, Matthias U. Liepe

Research output: Contribution to journal › Article › peer-review

7 Scopus citations

Abstract

Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate the surface compositions, structural profiles, and valence distributions of oxides, carbides, and impurities on niobium (Nb) and niobium-tin (Nb₃Sn) in situ under different processing conditions. We establish the underlying mechanisms of vacuum baking and nitrogen processing in Nb and demonstrate that carbide formation induced during high-temperature baking, regardless of gas environment, determines subsequent oxide formation upon air exposure or low-temperature baking, leading to modifications of the electron population profile. Our findings support the combined contribution of surface oxides and second-phase formation to the outcome of ultra-high vacuum baking (oxygen processing) and nitrogen processing. Also, we observe that vapor-diffused Nb₃Sn contains thick metastable oxides, while electrochemically synthesized Nb₃Sn only has a thin oxide layer. Our findings reveal fundamental mechanisms of baking and processing Nb and Nb₃Sn surface structures for high-performance superconducting RF and quantum applications.

Original language	English
Article number	115030
Journal	Superconductor Science and Technology
Volume	36
Issue number	11
DOIs	https://doi.org/10.1088/1361-6668/acff23
State	Published - Nov 2023
Externally published	Yes

Funding

This work was supported by the US National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Utilization of the PHI Versaprobe III XPS within UVa’s Nanoscale Materials Characterization Facility was fundamental to this project; we acknowledge NSF MRI Award 1626201 for the acquisition of this instrument. This work also made use of the Cornell Center for Materials Research Shared Facilities which are supported through the NSF MRSEC program (DMR-1719875), and was performed in part at the Cornell NanoScale Facility, an NNCI member supported by NSF Grant NNCI-2025233. Z S thanks H G Conklin and T M Gruber for assisting with sample preparation and Dr M Salim for XPS assistance. This work was supported by the US National Science Foundation under Award PHY-1549132, the Center for Bright Beams. Utilization of the PHI Versaprobe III XPS within UVa’s Nanoscale Materials Characterization Facility was fundamental to this project; we acknowledge NSF MRI Award # 1626201 for the acquisition of this instrument. This work also made use of the Cornell Center for Materials Research Shared Facilities which are supported through the NSF MRSEC program (DMR-1719875), and was performed in part at the Cornell NanoScale Facility, an NNCI member supported by NSF Grant NNCI-2025233. Z S thanks H G Conklin and T M Gruber for assisting with sample preparation and Dr M Salim for XPS assistance.

Keywords

carbide
impurity
niobium
niobium-tin
oxide
superconducting radio-frequency
surface

Access to Document

10.1088/1361-6668/acff23

Cite this

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title = "Surface oxides, carbides, and impurities on RF superconducting Nb and Nb3Sn: a comprehensive analysis",

abstract = "Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate the surface compositions, structural profiles, and valence distributions of oxides, carbides, and impurities on niobium (Nb) and niobium-tin (Nb3Sn) in situ under different processing conditions. We establish the underlying mechanisms of vacuum baking and nitrogen processing in Nb and demonstrate that carbide formation induced during high-temperature baking, regardless of gas environment, determines subsequent oxide formation upon air exposure or low-temperature baking, leading to modifications of the electron population profile. Our findings support the combined contribution of surface oxides and second-phase formation to the outcome of ultra-high vacuum baking (oxygen processing) and nitrogen processing. Also, we observe that vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental mechanisms of baking and processing Nb and Nb3Sn surface structures for high-performance superconducting RF and quantum applications.",

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author = "Zeming Sun and Zhaslan Baraissov and Dukes, \{Catherine A.\} and Dare, \{Darrah K.\} and Thomas Oseroff and Thompson, \{Michael O.\} and Muller, \{David A.\} and Liepe, \{Matthias U.\}",

note = "Publisher Copyright: {\textcopyright} 2023 The Author(s). Published by IOP Publishing Ltd.",

year = "2023",

month = nov,

doi = "10.1088/1361-6668/acff23",

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T2 - a comprehensive analysis

AU - Sun, Zeming

AU - Baraissov, Zhaslan

AU - Dukes, Catherine A.

AU - Dare, Darrah K.

AU - Oseroff, Thomas

AU - Thompson, Michael O.

AU - Muller, David A.

AU - Liepe, Matthias U.

PY - 2023/11

Y1 - 2023/11

N2 - Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate the surface compositions, structural profiles, and valence distributions of oxides, carbides, and impurities on niobium (Nb) and niobium-tin (Nb3Sn) in situ under different processing conditions. We establish the underlying mechanisms of vacuum baking and nitrogen processing in Nb and demonstrate that carbide formation induced during high-temperature baking, regardless of gas environment, determines subsequent oxide formation upon air exposure or low-temperature baking, leading to modifications of the electron population profile. Our findings support the combined contribution of surface oxides and second-phase formation to the outcome of ultra-high vacuum baking (oxygen processing) and nitrogen processing. Also, we observe that vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental mechanisms of baking and processing Nb and Nb3Sn surface structures for high-performance superconducting RF and quantum applications.

AB - Surface structures on radio-frequency (RF) superconductors are crucially important in determining their interaction with the RF field. Here we investigate the surface compositions, structural profiles, and valence distributions of oxides, carbides, and impurities on niobium (Nb) and niobium-tin (Nb3Sn) in situ under different processing conditions. We establish the underlying mechanisms of vacuum baking and nitrogen processing in Nb and demonstrate that carbide formation induced during high-temperature baking, regardless of gas environment, determines subsequent oxide formation upon air exposure or low-temperature baking, leading to modifications of the electron population profile. Our findings support the combined contribution of surface oxides and second-phase formation to the outcome of ultra-high vacuum baking (oxygen processing) and nitrogen processing. Also, we observe that vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental mechanisms of baking and processing Nb and Nb3Sn surface structures for high-performance superconducting RF and quantum applications.

KW - carbide

KW - impurity

KW - niobium

KW - niobium-tin

KW - oxide

KW - superconducting radio-frequency

KW - surface

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