Fig. 3: Resonant neutron reflectivity during hydrogen loading.

a Typical peak profiles in Q-scan mode on sample 1 at the V6 reflectometer. b Time dependent shift (left scale) and corresponding hydrogen concentration (right scale) of the resonance peak shown in panel a. c Simulated shift of the resonance peak for homogeneous H distribution along the film depth and no thickness changes (gray), for homogeneous distribution with 10% thickness change (red), and concentration gradient of H along the layer depth (green). Inset: SLD profiles of different models used for the simulations in panel c. d Resonance peak measured before and after incorporation of 85 at.% of H on sample 2 at the NREX reflectometer. The lines are the results of fits to Gaussian profiles. The wavevector Q^* used for the fixed-Q mode shown in panel e and f is indicated. e Time evolution of the intensity at Q^* (green points), and electrical resistance (black points) during H absorption. f Closeup of the fixed-Q data in panel e, before H₂ gas was injected into the vacuum chamber (red data points), right after injection (yellow points), and after an H-induced change of the reflectivity was detected outside the standard deviation σ (green points). Resistance data points are shown for comparison in black. Error bars indicate the statistical error.