An electrochromic mirror electrode based on reversible uptake of hydrogen in nickel magnesium alloy films is reported. Thin, magnesium-rich Ni-Mg films prepared on glass substrates by cosputtering from Ni and Mg targets are mirror-like in appearance and have low visible transmittance. Upon exposure to hydrogen gas or on cathodic polarization in alkaline electrolyte, the films take up hydrogen and become transparent. When hydrogen is removed, the mirror properties are recovered. The transition is believed to result from reversible formation of Mg 2 NiH 4 and MgH 2 . A thin overlayer of palladium was found to enhance the kinetics of hydrogen insertion and extraction, and to protect the metal surface against oxidation.Devices capable of switching between mirror and transparent states may find applications in architectural and transportation energy conservation, lighting and displays, aerospace insolation control, and optical communications systems. Switchable mirrors based on rare earth hydrides were discovered by Huiberts et al., 1 who observed a reversible metal-to-insulator transition when a thin film (150 to 500 nm) of yttrium or lanthanum coated with a thin layer of palladium was exposed to hydrogen gas. The transition accompanies conversion of a metallic dihydride phase to a semiconducting trihydride. Rare earth-magnesium alloy films 2 were subsequently found to be superior to the pure lanthanides in maximum transparency and mirror-state reflectivity. Phase separation appears to occur when these alloys take up hydrogen, giving transparent MgH 2 and LnH 2-3 , both of which may participate in the switching mechanism. 3 Because the rare earths are highly vulnerable to oxidation, a Pd overlayer at least 5 nm thick is required for films exposed to air or to an alkaline electrolyte. Although the Pd catalyzes the uptake and removal of hydrogen, it limits the maximum transparency of the composite film to about 50%. 4 The influence of the Pd layer and of a Pd/AlO x composite cap layer on hydrogen uptake by rare earth-based films have been studied extensively by van Gogh et al. 5 and by van der Molen et al. In the case of nickel, a stoichiometric alloy phase, Mg 2 Ni, with the same Mg-Ni ratio as in the hydride, can be prepared from the elements. In Mg 2 Ni (Fig. 1a), there are Ni-Ni bonds (shown as hollow rods), two types of Ni-Mg bonds (solid rods) and three types of Mg-Mg bonds (not shown).10 The Ni-Ni bonds and Mg-Mg bonds are shorter in the alloy than in the pure elements. The alloy absorbs hydrogen without structural rearrangement up to a composition of Mg 2 NiH 0.3 .7 This phase has metallic properties similar to those of the pure alloy. Further introduction of hydrogen produces Mg 2 NiH 4 (Fig. 1b) Ni-Mg films were deposited by DC magnetron co-sputtering from 2 in diameter Ni and Mg (99.98%) targets onto glass substrates with and without transparent conductive coatings. The base pressure was 1.4 x 10 -7 Torr, process pressure 2 mTorr, Ni power 20 W, Mg power 22 W, target-tosubstrate distance 7.5 cm. Dep...

A series of ZnO1−xSx films with 0⩽x⩽1.0 was deposited by radio-frequency reactive sputtering on different substrates. The structural characterization by x-ray diffraction measurements revealed that the films have wurtzite symmetry and correlated investigations of the layer composition by photoelectron spectroscopy showed that the lattice constant varies linearly with x. The composition dependence of the band gap energy in the ternary system was determined by optical transmission and the optical bowing parameter was found to be about 3eV.

Thin, Pd-capped metallic films containing magnesium and first row transition metals (Mn, Fe, Co) switch reversibly from their initial reflecting state to visually transparent states when exposed to gaseous hydrogen or following cathodic polarization in an alkaline electrolyte. Reversion to the reflecting state is achieved by exposure to air or by anodic polarization. The films were prepared by co-sputtering from one magnesium target and one manganese, iron, or cobalt target. Both the dynamic optical switching range and the speed of the transition depend on the magnesium-transition metal ratio. Infrared spectra of films in the transparent, hydrided (deuterided) states support the presence of the intermetallic hydride phases Mg 3 MnH 7 , Mg 2 FeH 6 , and Mg 2 CoH 5 . * Following the discovery of the switchable mirror phenomenon in yttrium and lanthanum hydrides by Huiberts et al., 1 similar behavior was reported in rare earth-magnesium alloy films. 2 Recently, metaltransparent hydride switching was also found in nickel-magnesium thin films. 3 In all of these systems, a thin Pd overlayer (generally > 5 nm) is applied to catalyze absorption and desorption of hydrogen and to protect the readily oxidized rare earth and/or Mg from oxidation. Infrared internal reflectance spectroscopy was used to characterize the transparent Ni-Mg hydride films as a mixture of Mg 2 NiH 4 and MgH 2 . 3 Other ternary hydrides containing magnesium and a first row transition metal include Mg

Structural and electronic properties of co-sputtered Ni-Mg thin films with varying Ni to Mg ratio were studied by in-situ x-ray absorption spectroscopy in the Ni L-edge and

We report on temperature-dependent Hall-effect measurements and secondary ion mass spectroscopy on unintentionally doped, n-type conducting GaN epitaxial films. Over a wide range of free carrier concentrations we find a good correlation between the Hall measurements and the atomic oxygen concentration. We observe an increase of the oxygen concentration close to the interface between the film and the sapphire substrate, which is typical for the growth technique used (synthesis from galliumtrichloride and ammonia). It produces a degenerate n-type layer of ≈1.5 μm thickness and results in a temperature-independent mobility and Hall concentration at low temperatures (<50 K). The gradient in free carrier concentration can also be seen in spatially resolved Raman and cathodoluminescence experiments. Based on the temperature dependence of the Hall-effect, Fourier transform infrared absorption experiments, and photoluminescence we come to the conclusion that oxygen produces a shallow donor level with a binding energy comparable to the shallow Si donor.