Electron-to-phonon dominated heat transport switching in Pd-capped SmHx thin films

Samarium-based switchable mirror films were synthesized by reactive DC sputtering and capped with a thin Pd layer to activate hydro-/dehydrogenations. The reversible transformation among Sm, SmH2, and hydrogen-rich SmH2+δ (δ: close to 1.0) was monitored in real time through optical, structural, electrical, and thermophysical measurements. By applying a picosecond time-domain thermoreflectance technique, we quantified the thermal transport properties of the hydride films under controlled atmospheres. The transition between the metallic and semiconducting states produced a large contrast in thermal conductivity, ranging from ∼13 W m−1 K−1 in the dehydrogenated phase to about 1.3 W m−1 K−1 after hydrogen uptake. This substantial modulation demonstrates that SmHx films function as effective thin-film thermal switching elements driven by the hydrogen gasochromic reactions.