Switching behavior and cycling durability on TiO2 coated Mg4Ni thin film mirror - Essay Example

Transmittance of the mirrors that were coated with the TiO2 film in the transparent state is improved by interference of multiple layers. Switching responses of multilayer thin films (Pd/Ti/Mg4Ni) was not effected by the outermost coatings of the TiO2 films, that is, hydriding and dehydriding speeds almost the same compared to the uncoating mirrors. Magnesium [1-3] and magnesium-based thin films [4-9] with a cap layer of Pd that can be switched between transparent and mirror states by hydrogen gas loading have attracted attention for their potential applications as smart windows, optical switches, and hydrogen sensors.

Among various switchable mirror materials, magnesium-nickel alloy thin films [5-7] are one of the most promising candidates for practical use of a switchable mirror from the point of view of material cost and optical switching performance. It shows, however, fast degradation like other switchable mirror materials; after about 150 switching cycles it can not be switched again [10]. This low stability is the most severe obstacle for their applications. The investigation of the degradation mechanism indicates that the formation of magnesium oxides at the outermost surface and failure of the Pd cap layer are the major causes of the degradation [10].

Magnesium in the thin film of Mg-Ni is easy diffusing towards the outermost surface during the hydrogenation and dehydrogenation processing due to the fact that the total energy is reduced by the segregation of the Mg to the surface [11]. The researchers have developed various devises to extend the lifetime of this mirror system for practical applications. For this purpose, the various polymer materials have been used as a protection layer by spin coating to surface of the mirror [12], and the hydrogen diffusion metals such as Ti, Nb and V as a protection layer inserted to the Pd top layer and the Mg-Ni thin layer period [13].

Polymer coatings can extend the switching