Thin films of Mg2NiHx which exhibit a remarkable black state with low reflection over the entire visible spectrum were investigated. The films show zero transmission and a low electrical resistivity. It was shown that such a black state is not explicable for a homogeneous layer. The results show that a large absorption coefficient yields substantial reflection.

In-situ deposited YH2 films ranging from epitaxial to nanocrystalline were prepared by pulsed laser deposition (PLD). PLD has the advantage that the yttrium target acts as a hydrogen source. Comparing the switching behavior to that of MBE-grown, ex-situ loaded films, the PLD-films show a reduced optical and electrical contrast in switching, which is probably due to the formation of Y(OH)3. On the other hand, we found that in the nanocrystalline PLD-films the hysteresis in switching is absent. Moreover, these films have a smoother surface morphology. Both effects are important for the implementation of switchable rare earth hydride films in all-solid-state devices.