[Hybrid] In situ hydrogen absorption in thin films with resonant neutron reflectometry

by Laura Guasco (Max Planck Insitute for Solid State Research)

Monday 14 Nov 2022, 14:30 → 15:30 Europe/Berlin

PH HS 3 (Physics Department)

The study of hydrogen diffusion and storage in different materials is crucial in the challenge of an actual implementation of sustainable energy sources, but also to explore the possible modification of electronic, magnetic and optical properties of the host materials. Due to high sensitivity of neutrons to hydrogen atoms, neutron scattering techniques have been successfully used for many decades. Neutron reflectometry in particular is demonstrated to be a powerful method for the study of hydrogen absorption in thin films for atomic concentrations of 5% and higher. In this talk we will show a new model-free method which allows to measure smaller (<5%) concentrations of hydrogen absorbed in situ, with smaller counting times and with a higher sensitivity. The method is based on measuring the position of the resonance formed due to the contrast between the optical potential of a layer and its neighbours. Hydrogen absorption leads to a change of this optical potential and hence to a shift of the resonance position. We will present experiments conducted on Al2O3/Nb(x)/Co(3nm)/Nb(x)/Pt(3nm) thin films demonstrating that hydrogen concentrations below 1% and absorption kinetics of few seconds can be measured using this method. 
Thanks to the combined information given by in situ XRR and RNR performed at NREX, we were able to observe peculiarities in the absorption process of niobium, a well-known H-absorber largely studied in the past, that were never reported before. In this talk we will discuss the current results as well as give a brief overview on possible future perspectives and further insights which can be achieved by combining neutrons simultaneously with different complementary techniques."

[1] L. Guasco, Y. Khaydukov et al., “’Resonant neutron reflectometry for hydrogen detection”, Nature Communications 13 1486 (2022)
[2] L. Guasco, Y. Khaydukov et al., “Kinetics of hydrogen absorption in niobium films with RNR”, in perparation