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)Nbx 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.

Hydrogen sorption in crystalline and amorphous Mg–Cu thin films

“…In this respect, the sorption behavior of the current films, are quite similar to that found in Mg-based ultra thin films [22][23][24][25][26][27][28][29][30], i.e. thickness <100 nm, where they hydrogenate and dehydrogenate in nearambient conditions.…”

“…Desorption temperatures are generally much lower for films of 15-100 nm thickness [22][23][24][25][26][27][28][29][30]. Qu et al [24] sputter deposited 100 nm Mg films on Si and glass substrates, and the resulting films were X-ray amorphous and could desorp hydrogen in air at temperatures of 298-328 K. Similarly, Richardson et al [26] produced Mg-Ni films of 80 nm thickness on a glass substrate and examined their optical switching properties.…”

Switchable mirror based on Mg–Zr–H thin films

“…As shown in Fig. 7, the surface of Mg-Zr thin film before hydrogen gas loading is very similar to Mg-Ti [12] and Mg-Nb [13] thin films, that is consisted with particle of the form of island. This tendency is clear with increase of the content of Zr.…”

“…These magnesium based alloys show the high hydrogen capacity (3-5.5 wt%) and the reversible hydrogen absorbing and desorbing characterizations. These materials also can be used as a 'switchable mirror', which is a new kind of optical switching material and is switched between transparent and mirror states by hydrogenation and dehydrogenation of thin film [12][13][14]. We studied Mg y TiH x and Mg y NbH x thin films with a thin Pd top-layer as a switchable mirror and reported that they show good optical switching properties.…”

Development of switchable mirror glass

“…This color is not considered preferable for use in the windows of buildings and vehicles. Therefore, we conducted research for improving the color neutrality in the transparent state, and found that almost coloreless transparency can be obtained in cases of hydrogenation by using the Mg-Ti alloy [14] or Mg-Nb alloy [15] as the switching layer. However, although the MgTi alloy thin film or Mg-Nb alloy thin film is colorless in the transparent state, the visible light transmittance is inferior compared to the Mg-Ni alloy thin film.…”