Selective thermal evolution of native oxide layer in Nb and Nb3Sn-coated SRF grade Nb: An in-situ angular XPS study

This contribution discusses the results of an in-situ angular XPS study on the thermal evolution of the native oxide layer on Nb3Sn and pure Nb. XPS data were recorded with conventional spectrometers using an AlK(alpha) X-ray source for spectra collected up to 600 C, and an MgK(Alpha) X-rays source for temperatures above 600 C. The effect of the thickness, composition, and thermal stability of that oxide layer is relevant to understanding the functional properties of superconducting radiofrequency (SRF) cavities used in particle accelerators. There is a consensus that oxide plays a role in surface resistance (Rs). The focus of this study is Nb3Sn, which is a promising material that is used in the manufacturing of superconducting radiofrequency (SRF) cavities as well as in quantum sensing, and pure Nb, which was included in the study for comparison. The thermal evolution of the oxide layer in these two materials is found to be quite different, which is ascribed to the influence of the Sn atom on the reactivity of the Nb atom in Nb3Sn films. Nb and Sn atoms in this intermetallic solid have different electronegativity, and the Sn atom can reduce electron density around neighbouring Nb atoms in the solid, thus reducing their reactivity for oxygen. This is shown in the thickness, composition, and thermal stability of the oxide layer formed on Nb3Sn. The XPS spectra were complemented by grazing incident XRD patterns collected using the ESRF synchrotron radiation facility. The results discussed herein shed light on oxide evolution in the Nb3Sn compound and guide its processing for potential applications of the Nb3Sn-based SRF cavities in accelerators and other superconducting devices.

[1]  M. Liepe,et al.  Nb3Sn Superconducting Radiofrequency Cavities: a Maturing Technology for Particle Accelerators and Detectors , 2022, 2203.06752.

[2]  T. Junginger,et al.  Origin of dielectric loss at the Nb/oxide interface: Evidence for atomic two-level systems , 2022 .

[3]  D. F. Ogletree,et al.  Elucidating the local atomic and electronic structure of amorphous oxidized superconducting niobium films , 2021, Applied Physics Letters.

[4]  S. C. Joshi,et al.  Evolution of surface oxides and impurities in high vacuum heat treated Nb: A TEM and TOF-SIMS in-situ study, mechanism and repercussions on SRF cavity applications , 2020 .

[5]  K. Fleischer,et al.  Oxidation of Nb(110): atomic structure of the NbO layer and its influence on further oxidation , 2020, Scientific Reports.

[6]  A. Grassellino,et al.  Ultralow Surface Resistance via Vacuum Heat Treatment of Superconducting Radio-Frequency Cavities , 2019, Physical Review Applied.

[7]  C. Hartmann,et al.  Preparation and in-system study of SnCl2 precursor layers: towards vacuum-based synthesis of Pb-free perovskites , 2018 .

[8]  Y. Ménesguen,et al.  Measurement of K fluorescence yields of niobium and rhodium using monochromatic radiation , 2017 .

[9]  D. Schuster,et al.  Understanding Quality Factor Degradation in Superconducting Niobium Cavities at Low Microwave Field Amplitudes. , 2017, Physical review letters.

[10]  S. Posen,et al.  Nb3Sn superconducting radiofrequency cavities: fabrication, results, properties, and prospects , 2017 .

[11]  U. Pudasaini,et al.  Progress With Multi-Cell Nb3Sn Cavity Development Linked With Sample Materials Characterization , 2015 .

[12]  M. Pellin,et al.  Analysis of Nb3Sn surface layers for superconducting radio frequency cavity applications , 2015, 1503.03410.

[13]  R. Tao.  Characterization of Nb Superconducting Radio Frequency Cavities Based On In-Situ STEM And EELS , 2013 .

[14]  M. Seah.  Summary of ISO/TC 201 Standard: ISO 14701:2011 – Surface chemical analysis – X‐ray photoelectron spectroscopy—measurement of silicon oxide thickness , 2012 .

[15]  Olexander S. Romanenko,et al.  Surface Characterization Of Nb Cavity Sections - Understanding The High Field Q-Slope , 2009 .

[16]  Hasan Padamsee,et al.  RF Superconductivity: Science, Technology, and Applications , 2009 .

[17]  A. Stierle,et al.  X-ray investigation of subsurface interstitial oxygen at Nb/oxide interfaces , 2008 .

[18]  M. Delheusy.  X-ray investigation of Nb/O interfaces , 2008 .

[19]  Tod Schneider,et al.  Oriented monolayers prepared from lyotropic chromonic liquid crystal. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[20]  D. Briggs,et al.  Surface Analysis by Auger and X-Ray Photoelectron Spectroscopy , 2003 .

[21]  H. Safa.  HIGH FIELD BEHAVIOR OF SCRF CAVITIES , 2001 .

[22]  G. Moretti.  Auger parameter and Wagner plot in the characterization of chemical states by X-ray photoelectron spectroscopy: a review , 1998 .

[23]  G. Gemme,et al.  XPS characterization of niobium for RF cavities , 1998 .

[24]  T. Hattori,et al.  Ultraclean surface processing of silicon wafers : secrets of VLSI manufacturing , 1998 .

[25]  M. Morita.  Native Oxide Films and Chemical Oxide Films , 1998 .

[26]  M. Schmal,et al.  Niobium Carbide Synthesis from Niobium Oxide: Study of the Synthesis Conditions, Kinetics, and Solid-State Transformation Mechanism , 1996 .

[27]  E. M. Savitskii,et al.  Physics and Metallurgy of Superconductors / Metallovedenie, Fiziko-Khimiya I Metallozipika Sverkhprovodnikov / Металловедение Физико-Химип и Металлофизика Сверхпроводников , 1995 .

[28]  J. Halbritter,et al.  On the oxidation and on the superconductivity of niobium , 1987 .

[29]  M. Beasley,et al.  RF surface resistance in Nb 3 Sn thin films , 1985 .

[30]  A. V. Kessel.  Electronic structure and Fermi surface properties of Nb3Sn and Nb3Sb , 1981 .

[31]  J. Halbritter,et al.  XPS and AES studies on oxide growth and oxide coatings on niobium , 1980 .

[32]  S. M. Barlow,et al.  The M4,5N4,5N4,5 Auger spectrum of tin and oxidised tin , 1979 .

[33]  T. Fehlner,et al.  Photoelectron spectroscopy of tin compounds , 1973 .

[34]  V. Kuznetsova,et al.  Phase Diagram of the Nb—Sn System , 1970 .

[35]  L. G. Parratt.  Surface Studies of Solids by Total Reflection of X-Rays , 1954 .