Atomic-Scale Chemical-Analyses of Niobium for Superconducting Radio-Frequency Cavities

Yoon, Kevin E.; Seidman, D. N.; Bauer, P.; Boffo, C.; Antoine, C.

doi:10.1109/tasc.2007.898059

Cited by 9 publications

(7 citation statements)

References 15 publications

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“…This does not seem to be the case for high RRR Nb: images of the oxide layer by transmission electron microscopy (TEM) on both single-crystal [47] and fine-grain [15] Nb samples showed a very uniform oxide layer with thickness ranging from 5 to about 8 nm and no significant suboxide region. This was also confirmed by atom probe tomography (APT) [52]. The existence of a more uniform oxide layer on high-purity Nb provides a better protective layer against hydrogen absorption, as suggested by the results in Sec.…”

Section: Discussion Of Experimental Resultssupporting

confidence: 55%

High fieldQslope and the baking effect: Review of recent experimental results and new data on Nb heat treatments

Ciovati

Myneni

Stevie

et al. 2010

Phys. Rev. ST Accel. Beams

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The performance of superconducting radio-frequency (SRF) cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing rf losses (high-field Q slope), in the absence of field emission, which are often mitigated by low-temperature (100-140 C, 12-48 h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field Q slope will be presented for cavities that had been heat treated in a vacuum furnace at high temperature without subsequent chemical etching. These studies are aimed at understanding the role of hydrogen on the highfield Q slope and at the passivation of the Nb surface during heat treatment. Improvement of the cavity performances, particularly of the cavities' quality factor, have been obtained following the hightemperature heat treatments, while secondary ion mass spectroscopy surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments.

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Section: Discussion Of Experimental Resultssupporting

confidence: 55%

High fieldQslope and the baking effect: Review of recent experimental results and new data on Nb heat treatments

Ciovati

Myneni

Stevie

et al. 2010

Phys. Rev. ST Accel. Beams

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“…More recently, two studies performed on niobium tips by means of three-dimensional local-electrode atom-probe tomography came to contradictory results (maybe due to slightly different preparation procedures of the Nb tips). Sebastian et al (2006) observed a smooth transition from near-stoichiometric Nb 2 O to near-stoichiometric Nb 2 O 5 on the surface of the Nb tip, whereas Yoon et al (2007) observed no continuous transition but a surface layer with an almost constant composition that can be interpreted by a mixture of NbO and NbO 2 .…”

Section: Discussionmentioning

confidence: 99%

EELS of Niobium and Stoichiometric Niobium-Oxide Phases—Part I: Plasmon and Near-Edges Fine Structure

et al. 2009

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A comprehensive electron energy-loss spectroscopy study of niobium (Nb) and stable Nb-oxide phases (NbO, NbO2, Nb2O5) was carried out. In this work (Part I), the plasmons and energy-loss near-edge structures (ELNES) of all relevant Nb edges (Nb-N2,3, Nb-M4,5, Nb-M2,3, Nb-M1, and Nb-L2,3) up to energy losses of about 2600 eV and the O-K edge are analyzed with respect to achieving characteristic fingerprints of Nb in different formal oxidation states (0 for metallic Nb, +2 for NbO, +4 for NbO2, and +5 for Nb2O5). Chemical shifts of the Nb-N2,3, Nb-M4,5, Nb-M2,3, and Nb-L2,3 edges are extracted from the spectra that amount to about 4 eV as the oxidation state increases from 0 for Nb to +5 for Nb2O5. Four different microscopes, including a 200 keV ZEISS Libra with monochromator, were used. The corresponding wide range of experimental parameters with respect to the primary electron energy, convergence, and collection semi-angles as well as energy resolution allows an assessment of the influence of the experimental setup on the ELNES of the different edges. Finally, the intensity of the Nb-L2,3 white-line edges is correlated with niobium 4d-state occupancy in the different reference materials.

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Section: Introductionmentioning

confidence: 99%

“…Oxygen and oxide formation on pure Nb surfaces were studied utilizing X-ray diffraction techniques (Ma & Rosenberg, 2003;Delheusy et al, 2008). Earlier, LEAP tomographic studies were successfully employed for studying the formation of niobium oxides on Nb surfaces (Sebastian et al, 2006;Yoon et al, 2007Yoon et al, , 2008 The behavior of hydrogen interstitial atoms is of paramount importance because niobium has a body-centered cubic (b.c.c.) structure containing octahedral and tetrahedral interstitial sites, and hydrogen atoms can migrate randomly on them and form different hydrides (NbH x ) (Schober, 1975a(Schober, , 1975b.…”

Section: Introductionmentioning

confidence: 99%

Atom-Probe Tomographic Analyses of Hydrogen Interstitial Atoms in Ultrahigh Purity Niobium

Kim¹,

Seidman

2015

Microsc Microanal

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Atomic-scale characterization of hydrogen and formation of niobium hydrides, using ultraviolet (wavelength=355 nm) picosecond laser-assisted local-electrode atom-probe tomography, was performed for ultrahigh purity niobium utilizing different laser pulse energies, 10 or 50 pJ/pulse or voltage pulsing. At 50 pJ/pulse, hydrogen atoms migrate onto the 110 and 111 poles as a result of stimulated surface diffusion, whereas they are immobile for <10 pJ/pulse or for voltage pulsing. Accordingly, the highest concentrations of H and NbH were obtained at 50 pJ/pulse. This is attributed to the thermal energy of the laser pulses being transferred to pure niobium specimens. Therefore, we examined the effects of the laser pulse energy being increased systematically from 1 to 20 pJ/pulse and then decreasing it from 20 to 1 pJ/pulse. The concentrations of H, H2, and NbH and the atomic concentration ratios H2/H, NbH/Nb, and Nb3+/Nb2+ were calculated with respect to the systematically changing laser pulse energies. The atomic concentration ratios H2/H and NbH/Nb are greater when decreasing the laser pulse energy than when increasing it, because the higher residual thermal energy after decreasing the laser pulse energy increases the mobility of H atoms by supplying sufficient thermal energy to form H2 or NbH.

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Atomic-Scale Chemical-Analyses of Niobium for Superconducting Radio-Frequency Cavities

Cited by 9 publications

References 15 publications

High fieldQslope and the baking effect: Review of recent experimental results and new data on Nb heat treatments

High fieldQslope and the baking effect: Review of recent experimental results and new data on Nb heat treatments

EELS of Niobium and Stoichiometric Niobium-Oxide Phases—Part I: Plasmon and Near-Edges Fine Structure

Atom-Probe Tomographic Analyses of Hydrogen Interstitial Atoms in Ultrahigh Purity Niobium

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