Surface characterization of nitrogen-doped Nb (100) large-grain superconducting RF cavity material
(100) Oriented niobium (Nb) crystals annealed in the vacuum conditions close to that used in mass production of 1.3 GHz superconducting radio frequency cavities for linear accelerators and treated in nitrogen at a partial pressure of 0.04 mbar at temperatures of 800 and 900 °C have been studied. The surfaces of the nitrogen-treated samples were investigated by means of various surface-sensitive techniques, including grazing-incidence X-ray diffraction, X-ray photoemission spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy in planar view and on cross-sections prepared by a focused ion beam. The appearance of a dense layer of epitaxial rectangular precipitates has been observed for the Niobium nitrided at 900 °C. Increased nitrogen concentration in the near-surface region was detected by glow-discharge optical-emission spectroscopy, focused ion-beam cross-sectional images and X-ray photoelectron spectroscopy. Crystalline phases of NbO and β-Nb2N were identified by X-ray diffraction. This information was confirmed by X-ray photoelectron measurements, which in addition revealed the presence of Nb2O5, NbON, NbN, and NbN x O y components on the surface. These results establish the near-surface Nb phase composition after high-temperature nitrogen treatment, which is important for obtaining a better understanding of the improved RF cavity performance.
Authors declare that no conflict of interests exist. Support on the material from Xenia Singer, and for the FIB preparation and the SEM analysis by S. Kulkarni at the DESY NanoLab, is acknowledged. We acknowledge the use of the focused ion-beam instrument at the DESY NanoLab funded by the BMBF Grant No. 5K13WC3 (PT-DESY). Authors GSD, AP, and BF acknowledge funding from the BMBF grant no. 05H15GURBB.
- 3.Ciovati G, Myneni G, Stevie F, Maheshwari P, Griffis D (2010) High field Q slope and the baking effect: review of recent experimental results and new data on Nb heat treatments. Phys Rev Accel Beams 13:02200Google Scholar
- 4.Grassellino A, Romanenko A, Trenikhina Y, Checchin M, Martinello M, Melnychuk OS, Chandrasekaran S, Sergatskov DA, Posen S, Crawford AC, Aderhold S, Bice D (2017) Unprecedented quality factors at accelerating gradients up to 45 MV/m in niobium superconducting resonators via low temperature nitrogen infusion. Supercond Sci Technol 30:094004CrossRefGoogle Scholar
- 5.Grassellino A, Romanenko A, Sergatskov D, Melnychuk O, Trenikhina Y, Crawford A, Rowe A, Wong M, Khabiboulline T, Barkov F (2013) Nitrogen and argon doping of niobium for superconducting radio frequency cavities: a pathway to highly efficient accelerating structures. Supercond Sci Technol 26:102001CrossRefGoogle Scholar
- 6.Grassellino A, Romanenko A, Posen S, Trenikhina Y, Melnychuk O, Sergatskov DA, Merio M, Checchin M, Martinello M (2015) N doping: progress in development and understanding. In: Proceedings SRF2015, Whistler, BC, Canada, MOBA06, pp 48–754Google Scholar
- 7.Trenikhina Y, Grassellino A, Barkov F and Romanenko (2013) A chemical structure of niobium samples vacuum treated in nitrogen in parallel with very high Q0 cavities. In: Proceedings SRF2013, Paris, France, TUP065, pp 583–585Google Scholar
- 8.Trenikhina Y, Grassellino A, Melnychuk O and Romanenko A (2015) Characterization of nitrogen doping recipes for the Nb SRF cavities. In: Proceedings SRF2015, Whistler, BC, Canada, MOPB055, pp 223–227Google Scholar
- 20.Series surface and acceptance test preparation of superconducting cavities for the European XFEL, Revision B/June 30, 2009, p 22Google Scholar
- 25.Albrecht WM and Goode Jr WD (1959) Reaction of nitrogen with niobium. Techn Rep BMI-1360, W-7405-ENG-92, Battelle Memorial Inst., Columbus, OhioGoogle Scholar
- 26.Batchelor A, Leonard D, Russell P, Stevie F, Griffis D and Myneni G (2007) TEM and SIMS Analysis of (100),(110), and (111) Single Crystal Niobium. In: AIP Conference Proceedings, pp 72–83Google Scholar
- 41.Dhakal P, Ciovati G, Myneni GR, Gray KE, Groll N, Maheshwari P, McRae DM, Pike R, Proslier T, Stevie F, Walsh RP, Yang Q, Zasadzinzki J (2013) Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity. Phys. Rev Spec Top Accel. Beams 16:042001CrossRefGoogle Scholar