title: Direct atomic-scale imaging of hydrogen and oxygen interstitials in pure niobium using atom-probe tomography and aberration-corrected scanning transmission electron microscopy.
abstract: 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 NbO(2), Nb(2)O(5), NbO, Nb stacking sequence; annular bright-field imaging is used to visualize directly hydrogen atoms in bulk β-NbH.
authors.affiliation: Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Yoon-Jun
authors.initials: YJ
authors.lastname: Kim
authors.forename: Runzhe
authors.initials: R
authors.lastname: Tao
authors.forename: Robert F
authors.initials: RF
authors.lastname: Klie
authors.forename: David N
authors.initials: DN
authors.lastname: Seidman
mesh_terms: D016477:Artifacts; D006859:Hydrogen / Q000032:analysis*; D008422:Materials Testing; D018625:Microscopy, Atomic Force / Q000379:methods*; D017348:Microscopy, Electron, Scanning Transmission / Q000379:methods*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D009556:Niobium / Q000737:chemistry*; D010100:Oxygen / Q000032:analysis*; D010316:Particle Size
chemical_list: D009556:Niobium; D006859:Hydrogen; D010100:Oxygen