  The applicability of standard methods for compositional analysis is limited
for H-containing films. Neutron reflectometry is a powerful, non-destructive
method that is especially suitable for these systems due to the large negative
scattering length of H. In this work we demonstrate how neutron reflectometry
can be used to investigate thin films of yttrium hydride. Neutron reflectometry
gives a strong contrast between the film and the surface oxide layer, enabling
us to estimate the oxide thickness and oxygen penetration depths. A surface
oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride
films.
