Optical properties and degradation mechanism of magnesium-niobium thin film switchable mirrors

Abstract

Magnesium-niobium (Mg-Nb) thin films with a palladium (Pd) top layer were prepared on glass substrates by means of DC magnetron sputtering deposition, at room temperature. A Mg-Nb thin film with a Pd top layer can be switched to a transparent state from a mirror-like state by loading with 4% hydrogen gas. The optical properties of Mg_(1-x)Nb_x thin film switchable mirrors, with x ranging from 0.13 to 0.37, coated with a Pd layer were investigated using a UV-Vis-NIR optical photometer. The optical transmittance of the hydride states decreased with an increasing Nb fraction. Mg-Nb thin film switchable mirrors show color-neutral characteristics in the hydride state. The degradation mechanism of Mg-Nb thin films when loading hydrogen (H) gas was studied using X-ray photoelectroscopy (XPS) and scanning electron microscope (SEM) methods. We showed that Mg-Nb-H thin films are transparent, color-neutral semiconductors with a band cap of 2.2 ± 0.2 eV.