W. Lohstroh

Mg-Ni-H films as selective coatings: Tunable reflectance by layered hydrogenation

Unlike other switchable mirrors, Mg2NiHx films show large changes in reflection that yield very low reflectance (high absorptance) at different hydrogen contents, far before reaching the semiconducting state. The resulting reflectance patterns are of interference origin, due to a self-organized layered hydrogenation mechanism that starts at the substrate interface, and can therefore be tuned by varying the film thickness. This tunability, together with the high absorptance contrast observed between the solar and the thermal energies, strongly suggests the use of these films in smart coatings for solar applications.

Stabilized switchable “black state” in Mg2NiH4∕Ti∕Pd thin films for optical hydrogen sensing

A triple layer thin film (30nm Mg2Ni∕100nm Ti∕10nm Pd sputtered on glass) switches reversibly from a shiny metallic to a “black” state upon exposure to moderate hydrogen pressure (≈5.103Pa). This black state resembles that obtained in thick Mg2NiHx layers and has the great advantage of being stable and easily controlled. Both the reversible high optical contrast (Rreflective∕Rblack≈10 in the red wavelength range) and the fast kinetics of hydrogen absorption and desorption make this material interesting for applications as optical hydrogen sensors.