Author: Zasadzinski, J.
Paper Title Page
WEPCAV001 Study of the Niobium Oxide Structure and Microscopic Effect of Plasma Processing on the Niobium Surface 585
 
  • B. Giaccone, M. Martinello
    Fermilab, Batavia, Illinois, USA
  • B. Giaccone, J. Zasadzinski
    IIT, Chicago, Illinois, USA
 
  A study of the niobium oxide structure is presented here, with particular focus on the niobium suboxides. Multiple steps of argon sputtering and XPS measurements were carried out until the metal surface was exposed. The sample was then exposed to air and the oxide regrowth was studied. In addition, three Nb samples prepared with different surface treatments were studied before and after being subjected to plasma processing. The scope is investigating the microscopic effect that the reactive oxygen contained in the glow discharge may have on the niobium surface. This study suggests that the Nb2O5 thickness may increase, although no negative change in the cavity performance is measured since the pentoxide is a dielectric.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-WEPCAV001  
About • Received ※ 22 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 13 January 2022 — Issue date ※ 16 May 2022
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FROFDV03 Investigating the Anomalous Frequency Variations Near Tc of Nb SRF Cavities 885
 
  • D. Bafia, M. Checchin, A. Grassellino, A.S. Romanenko
    Fermilab, Batavia, Illinois, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
 
  We report recent studies on the anomalous frequency variations of 1.3 GHz Nb SRF cavities near the transition temperature Tc and use them to investigate the underlying physics of state-of-the-art surface treatments. One such feature, a dip in frequency, correlates directly with the quality factor at 16 MV/m and the anti-Q slope that arise in cavities with dilute concentrations of N interstitial in the RF layer achieved via N-doping and mid temperature baking. For N interstitial, we find that the dip magnitude and Tc follow exponential relationships with the electronic mean free path. We present the first observation of the frequency dip near Tc in a cavity baked at 200 C in-situ for 11 hours, which is concurrent with the anti-Q slope, and may be driven by oxygen diffused from the native oxide, thus suggesting the possibility of ‘‘O-doping.’’ We also investigate the conductivities of two cavities that display different resonant frequency behaviors near Tc and suggest that the anti-Q slope and frequency dip phenomena may occur in the presence of interstitial N or possibly O that inhibit the formation of proximity coupled Nb nano-hydrides.  
slides icon Slides FROFDV03 [1.035 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-FROFDV03  
About • Received ※ 25 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 18 December 2021 — Issue date ※ 28 April 2022
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