Polycrystalline switchable mirrors

Recently, R nanoparticle layers [e.g., Y Bour et al. (2001), Gd Aruna et al. (2004)] have also been utilized as the active layer in the switchable mirrors. In these New generation switchable mirrors , in addition to the size dependent switchable properties, utilization of nanoparticle layers showed that it was possible to tune the band gap of the trihydride state by varying the nanoparticle size (Aruna et al., 2004) and sense very low concentrations of hydrogen (Bour et al., 2001). In a recent study, the use of Pd nanoparticle over layer to enhance the hydrogen induced switching properties of the Gd polycrystalline films has been reported (Aruna et al., 2005c). The studies are discussed in detail in section 4. 

The deposition and electrical characterization of R metal and R hydride films have been reported in the seventies (e.g., Curzon and Singh (1978, 1979)). Since the discovery of the switchable mirror effect, a variety of techniques have been utilized to deposit R metal polycrystalline and epitaxial films e.g., molecular beam deposition (e.g., Huiberts et al. (1996b)), sputter deposition (e.g., van der Sluis et al. (1997), van der Sluis and Mercier (2001), Mercier and van der Sluis (2001)), pulsed laser deposition (e.g.. Dam et al. (2003)) and thermal evaporation (e.g., Mor and Malhotra (2000)). Typically for pure R metals films, a base pressure of 10 Pa, is an essential requirement (Huiberts et al., 1996b Wildes et al., 1996). Where as room temperature deposition resulted in polycrystalline films, a higher substrate temperature was utilized for depositing epitaxial films. Due to the higher... 

As introduced in the previous section, the first generation switchable mirrors typically consist of polycrystalline or epitaxial R metal films (as the active layer) capped with a Pd over layer, deposited on a transparent substrate. 

Since its discovery, most of the work on switchable mirror effect has been devoted to the study of hydrogen-induced changes in optical, electronic and structural properties in polycrystalline R metal films, as summarized in the previous section. Though some studies have been reported on single-crystalline films, for example Y films on (110) W substrates (Hayoz et al., 1998) and epitaxial Y films deposited on Nb coated (110) AI2O3 substrates (Wildes et al., 1996 Remhof et al., 1997, 1999), these samples were not suitable for optical and elec-... 

This review summarize various studies carried out on different generations of rare earth metal switchable mirrors based on polycrystalline, epitaxial layers, rare earth-Mg alloys, rare earth-... 

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