Direct Atomic-Scale Imaging of Hydrogen and Oxygen Interstitials in Pure Niobium Using Atom-Probe Tomography and Aberration-Corrected Scanning Transmission Electron Microscopy

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• 作者：Yoon-Jun Kim ; Runzhe Tao ; Robert F. Klie ; David N. Seidman
• 刊名：ACS Nano
• 出版年：2013
• 出版时间：January 22, 2013
• 年：2013
• 卷：7
• 期：1
• 页码：732-739
• 全文大小：571K
• 年卷期：v.7,no.1(January 22, 2013)
• ISSN：1936-086X

文摘

Imaging the three-dimensional atomic-scale structure of complex interfaces has been the goal of many recent studies, due to its importance to technologically relevant areas. Combining atom-probe tomography and aberration-corrected scanning transmission electron microscopy (STEM), we present an atomic-scale study of ultrathin (5 nm) native oxide layers on niobium (Nb) and the formation of ordered niobium hydride phases near the oxide/Nb interface. Nb, an elemental type-II superconductor with the highest critical temperature (T_c = 9.2 K), is the preferred material for superconducting radio frequency (SRF) cavities in next-generation particle accelerators. Nb exhibits high solubilities for oxygen and hydrogen, especially within the RF-field penetration depth, which is believed to result in SRF quality factor losses. STEM imaging and electron energy-loss spectroscopy followed by ultraviolet laser-assisted local-electrode atom-probe tomography on the same needle-like sample reveals the NbO₂, Nb₂O₅, NbO, Nb stacking sequence; annular bright-field imaging is used to visualize directly hydrogen atoms in bulk 尾-NbH.

Keywords:

Nb; NbH; Nb oxides; atom-probe tomography; aberration-corrected STEM; annular bright-field images