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

Abstract

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.

Atomic‐Scale Structural and Chemical Study of Columnar and Multilayer Re–Ni Electrodeposited Thermal Barrier Coating

“…The composition of the dark layers was found to be similar to that at the intercolumnar grain boundaries. [47,48] The hydrogen concentrations (H/Nb atomic ratios in the range of 0.7-1.1) were found to be in reasonable agreement with the expected hydrogen concentrations. Figure 1a demonstrates that the surface crevices at intercolony boundaries may serve as preferred sites for crack propagation along intercolumnar GBs, due to the two types of boundaries trying to remain continuous.…”

“…A quantitative APT study of hydrogen in ultrahigh purity niobium that contains b-niobium-hydride (b-NbH) precipitates has been reported. [47,48] The hydrogen concentrations (H/Nb atomic ratios in the range of 0.7-1.1) were found to be in reasonable agreement with the expected hydrogen concentrations. While the concentrations of oxygen and hydrogen at the intercolumnar GBs are greater than at the bright layers within the grains, they are still significantly smaller than those typical of oxides and hydrides.…”

An Atomistic Tomographic Study of Oxygen and Hydrogen Atoms and their Molecules in CVD Grown Graphene

“…The quantification of oxygen data is similar to that of carbon, which is detected at a slightly lower concentration than is expected for the same reason . The hydrogen concentration in an APT experiment is also in reasonable agreement with the theoretical concentration of a metal hydride material . The hydrogen concentration can be increased by using the ultraviolet laser's pulse energy, to 10–50 pJ per pulse, and the crystallographic orientation of a sample (higher concentration at low index poles), which are related to the diffusion of hydrogen from the interior of an APT sample .…”

“…The hydrogen concentration in an APT experiment is also in reasonable agreement with the theoretical concentration of a metal hydride material . The hydrogen concentration can be increased by using the ultraviolet laser's pulse energy, to 10–50 pJ per pulse, and the crystallographic orientation of a sample (higher concentration at low index poles), which are related to the diffusion of hydrogen from the interior of an APT sample . The oxygen peaks may originate from O impurities adsorbed on Cu from O 2 in the air, before or after the growth of graphene .…”

Characterizing nanoscale precipitation in a titanium alloy by laser-assisted atom probe tomography

“…This should also limit the formation of complex molecular ions associated with TiH and TiO formation, which also depend on the partial pressures of H2 and O2 in the vacuum system. They are furthermore associated with the surface diffusivities of interstitial atoms [37]. Although the physical chemistry of gas-metal reactions in a high electric field is a complex topic and not the focus of this article, it is noted that a metal-hydride/oxide was formed with titanium at higher laser pulse energies.…”