Fig. 1: Resonant neutron reflectometry scheme.

a Sketch of the thin-film structure and geometry of the reflectometric measurements. Q is the wavevector transfer, and θ the scattering angle. b Depth profile of the scattering length density ρ of the sample before (blue line) and after (red line) incorporation of 85 at.-% hydrogen. c The numerically calculated neutron density enhancement (with respect to the incoming beam with \({\left|{{\Psi }}\right|}^{2}=1\)), along the film before (blue) and after (red) hydrogenation. For simplicity, the schematic does not include the H-induced swelling of the film.