Prudnikava, A.; Tamshevich, Y.; Kugeler, O.; Knobloch, J.; Babenkov, S.; Aristov, V.; Molodtsova, O.; Smirnov, D.; Makarova, A.: Synchrotron XPS Study of Niobium Treated with Nitrogen Infusion. In: Kenji Saito ... [Ed.] : SRF2021 - Proceedings of the 20th International Conference on RF SuperconductivityGeneva: JACoW, 2022. - ISBN 978-3-95450-233-2, p. MOPTEV006/1-5
https://srf2021.vrws.de/papers/moptev006.pdf
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Abstract:
Processing of niobium cavities with the so-called nitrogen infusion treatment demonstrates the improvement of efficiency and no degradation of maximal accelerating gradients. However, the chemical composition of the niobium surface and especially the role of nitrogen gas in this treatment has been the topic of many debates. While our study of the infused niobium using synchrotron X-ray Photoelectron Spectroscopy (XPS) showed modification of the surface sub-oxides surprisingly there was no evidence of nitrogen concentration build up during the 120°C baking step, irrespectively of N2 supply. Noteworthy, that the niobium contamination with carbon and nitrogen took place during a prolonged high-temperature anneal even in a high vacuum condition (10-8-10-9 mbar). Evidently, the amount of such contamination appears to play a key role in the final cavity performance