X射线光电子能谱
拉曼光谱
铌
材料科学
价(化学)
结合能
分析化学(期刊)
光谱学
氧化物
氧化铌
谱线
化学
核磁共振
原子物理学
冶金
物理
光学
有机化学
量子力学
色谱法
天文
作者
Nageshwar Singh,M. N. Deo,Mangla Nand,S. N. Jha,S. B. Roy
摘要
We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (residual resistivity ratio, ∼300) niobium (Nb) materials used in fabrication of superconducting radio frequency (SRF) cavities for particle accelerators. Raman spectroscopy of Nb materials (as-received from the vendor as well as after surface chemical- and thermal processing) revealed numerous peaks, which evidently show the presence of oxides (550 cm−1), hydrides (1277 and 1385 cm−1: ∼80 K temperature), and groups of hydrocarbons (1096, 2330, 2710, 2830, 2868, and 3080 cm−1). The present work provides direct spectroscopic evidence of hydrides in the electropolished Nb materials typically used in SRF cavities. Raman spectroscopy thus can provide vital information about the near-surface chemical species in niobium materials and will help in identifying the cause for the performance degradation of SRF cavities. Furthermore, photoelectron spectroscopy was performed on the Nb samples to complement the Raman spectroscopy study. This study reveals the presence of C and O in the Nb samples. Core level spectra of Nb (doublet 3d5/2 and 3d3/2) show peaks near 206.6 and 209.4 eV, which can be attributed to the Nb5+ oxidation state. The core level spectra of C 1 s of the samples are dominated by graphitic carbon (binding energy, 284.6 eV), while the spectra of O 1 s are asymmetrically peaked near binding energy of ∼529 eV, and that indicates the presence of metal-oxide Nb2O5. The valence-band spectra of the Nb samples are dominated by a broad peak similar to O 2p states, but after sputtering (for 10 min) a peak appears at ∼1 eV, which is a feature of the elemental Nb atom.
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