Resonant neutron reflectometry for hydrogen detection

Abstract

The detection and quantification of hydrogen is becoming increasingly important in research on electronic materials and devices, following the identification of the hydrogen content as a potent control parameter for the electronic properties. However, establishing quantitative correlations between the hydrogen content and the physical properties of solids remains a formidable challenge. Here we report neutron reflectometry experiments on 50 nm thick niobium films during hydrogen loading, and show that the momentum-space position of a prominent waveguide resonance allows tracking of the absolute hydrogen content with an accuracy of about one atomic percent on a timescale of less than a minute. Resonance-enhanced neutron reflectometry thus allows fast, direct, and non-destructive measurements of the hydrogen concentration in thin-film structures, with sensitivity high enough for real-time in-situ studies.

Topical Review of Quantum Materials and Heterostructures Studied by Polarized Neutron Reflectometry

“…In particular, the ability to track hydrogen gas and moisture content in films and correlate this with superconducting, electrical, or magnetic performance may become critical. In situ transport measurements, [98] [133] Copyright 2013, American Physical Society. c) Position-sensitive area detector image of scattering from a Co nanodot array grown on Co/Pd.…”

“…To demonstrate the precision of the resonant waveguide enhancement method and its ability to track changes of the sample properties, the authors of ref. [98] measured PNR simultaneously with the widely used, albeit indirect, electrical resistivity sampling approach. As shown in Figure 5d, after the introduction of hydrogen, the resonance position displays a linear time dependence which tracks with the sample resistance (i.e., a property of the sample known to depend sensitively on the hydrogen content).…”

“…Reproduced under the terms of the CC‐BY 4.0 License. [ 98 ] Copyright 2022, The Authors. Published by Springer Nature Limited.…”

“…In this direction, there is some promising technique‐development research aimed at increasing the sensitivity of PNR to hydrogen‐induced modifications by using resonant waveguide enhancement methods. [ 98–100 ] Figure 5c shows the waveguide peak of a Nb resonator measured by means of PNR. [ 98 ] By adding a thin FM layer with noncollinear magnetization (obtained, for example, with an easy axis canted to the applied magnetic field), a resonant enhancement of spin‐flip intensity is observed around the momentum transfer .…”

“…d) Fixed-Q scan at Q* (i.e., arbitrary point defined in (c) near the resonance position) and in situ resistance measurement during hydrogen exposure. Reproduced under the terms of the CC-BY 4.0 License [98]. Copyright 2022, The Authors.…”