Open AccessSystematic study of niobium thermal treatments for superconducting radio frequency cavities employing x-ray photoelectron spectroscopy
Author(s) -
Alena Prudnikava,
Yegor Tamashevich,
S. Babenkov,
Анна A. Макарова,
Д. А. Смирнов,
V. Yu. Aristov,
О. В. Молодцова,
Oliver Kugeler,
Jens Viefhaus,
B. Foster
Publication year - 2022
Publication title -
superconductor science and technology/superconductor science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.033
H-Index - 105
eISSN - 1361-6668
pISSN - 0953-2048
DOI - 10.1088/1361-6668/ac6a85
Subject(s) - niobium , x ray photoelectron spectroscopy , materials science , superconducting radio frequency , annealing (glass) , synchrotron , oxide , nitrogen , analytical chemistry (journal) , niobium oxide , photoemission spectroscopy , superconductivity , chemical engineering , metallurgy , chemistry , particle accelerator , optics , physics , beam (structure) , organic chemistry , chromatography , engineering , quantum mechanics
The structural and chemical composition of the surface layer (100-140 nm) of niobium radiofrequency cavities operating at cryogenic temperature has enormous impact on their superconducting characteristics. During the last years, cavities treated with a new thermal processing recipe, so-called nitrogen infusion, have demonstrated an increased efficiency and high accelerating gradients. The role and importance of nitrogen gas has been a topic of many debates. In the present work we employ variable-energy synchrotron X-ray photoelectron spectroscopy (XPS), to study the niobium surface subjected to the following treatments: vacuum annealing at 800°C, nitrogen infusion, and vacuum heat treatment as for the infusion process but without nitrogen supply. Careful analysis of XPS energy-distribution curves revealed a slightly increased thickness of the native oxide Nb2O5 for the infused samples (~3.8 nm) as compared to the annealed one (~3.5 nm) which indicates insignificant oxygen incorporation into niobium during 120°C baking and no effect of nitrogen on the formation of oxides or other niobium phases. By conducting an additional in-situ annealing experiment and analyzing the niobium after the failed infusion process, we conclude that the vacuum furnace hygiene particularly during the high-temperature stage is the prerequisite for success of any treatment recipe.