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Diamond-like carbon (DLC) films are prepared by bipolar-type plasma-based ion implantation and deposition (PBIID) using the combination of toluene (C7H8), tetramethylsilane (TMS: Si(CH3)4) and nitrogen (N2) as a source gas. The characteristics and mechanical properties of the films are examined by Raman spectroscopy and nanoindentation measurement, respectively. The film composition is evaluated by X-ray photoelectron spectroscopy (XPS). Raman analysis reveals that polymer-like structure is formed and increases with increasing Si content. The hardness and Young's modulus decrease with increasing Si content. The ratio of Si to C (Si:C) in the films is almost equal to that in the source gases. The addition of N2 together with TMS causes a slight increase of sp2 ring clusters and improvement of the mechanical properties probably due to the formation of Si N bonds. Moreover, the Si:C ratio in the films is enhanced by the N2 addition.

Poly(3,4-alkylenedioxythiophenes) (PXDOTs) electrochromic (EC) thin films were synthesized that exhibited novel gasochromic properties by casting catalytic platinum nanoparticles (PtNPs) on their surfaces. The PXDOTs cathodically colored EC films were composed of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-propylenedioxythiophene) (PProDOT), poly(3,4-(2,2-dimethylpropylenedioxy) thiophene) (PProDOT-Me 2 ), and poly(3,4-(2′,2′-diethylpropylene)-dioxythiophene) (PProDOT-Et 2 ). All the films were obtained by electrochemical deposition on a transparent conducting substrate. The PtNPs were selected as catalytic materials coupled with hydrogen gas (H 2 ) to reduce the PXDOTs films and showed GC properties. These films revealed significant optical transmittance changes (ΔT) when negative voltages were applied or the material was exposed to H 2 . The UV–vis spectra of films exposure to H 2 were similar to apply voltages between − 0.3 and − 0.4 V. The PProDOT-Me 2 film exhibited the highest ΔT (˃40%) and best long-term cyclic ability. By varying the casting concentration of PtNPs, the darkening times were dramatically reduced from ˃10 min to ˂1 min. Furthermore, ozone (O 3 ) was introduced to enhance bleaching and cyclic stability. The optimized 0.5 wt% PtNPs/ PProDOT-Me 2 film showed fast switching and a maximum ΔT of 50.7% during the first cycle, which was maintained after 120 cycles. The PtNPs/PXDOTs films were characterized and analyzed using cyclic voltammetry, UV–vis transmittance spectra, optical transmittance kinetic curves, surface electronic microscopy, and Fourier transform infrared spectroscopy.

New nickel oxyhydroxide/palladium (NiOOH/Pd) nanocomposites was prepared and showed novel gasochromic characteristics for the first time. The NiOOH microparticles were obtained using the chemical bath synthesis method without stirring for 72 h. The synthesized catalytic palladium nanoparticles (PdNPs) were added into the NiOOH microparticles and the NiOOH/Pd nanocomposites were readied for gasochromic application. The NiOOH/Pd nanocomposite thin film was obtained by using wet-coating methods. An obviously color change from black state NiOOH to white state Ni(OH) 2 was observed after exposed to hydrogen (H 2 ), the maximum transmittance change was 23.2% at 572 nm. The white Ni(OH) 2 state can be switched back to darken state by exposing to ozone (O 3 ) on the thin film with its novel gasochromic property. Surface electron microscopy (SEM) images showed special surface morphology of NiOOH/Pd before and after gas treatments. X-ray photoelectron spectroscopy (XPS) analysis was used to confirm the changes in chemical bonding before/after gas treatment. XRD patterns and FT-IR spectra indicated the structure changes that occurred during film preparation and before/after exposed to H 2.

We demonstrate high contrast gasochromism in a thin film produced by combining chromic Prussian blue nanoparticles and catalytic platinum nanoparticles, applied by sequential wet-coating onto a substrate. The contrast ratio at 700 nm reaches 80. The cycle stability exceeds 200 cycles. H2 with low concentration (4%-H2) and air can drive the change of colour between blue and colourless. We also reveal via X-ray diffraction, Fourier-transform IR spectroscopy, and investigation of the redox potential of a series of metal-substituted Prussian blue analogues, that bleaching results from the reduction of Prussian blue nanoparticles by protons generated using platinum nanoparticles.

La0.7Sr0.3MnO3 films were prepared on MgO substrates using direct current (DC) magnetron sputtering, and the optical indices ranging from ultraviolet to infrared wavelengths (0.03–5.0 eV) were evaluated using spectroscopic ellipsometry at sample temperatures between 278 K and 373 K. The free-carrier concentration and mobility were estimated using fitted parameters of the Drude term obtained from analysis of the ellipsometric angle spectra and DC electrical resistivity. The mobility decreased with increasing sample temperature up to ∼320 K, which was nearly equal to the metal–insulator transition temperature of the film. The mobility became constant at higher temperatures, whereas the concentration was almost constant relative to the sample temperature.

Gasochromic films can reversibly switch their optical transmittance upon alternating exposure to diluted H2 and O2 gases. These films are usually prepared by physical methods such as sputtering and pulsed-laser deposition. Here, we report a new method using UV irradiation for low-temperature chemical fabrication of Pt-WO3 gasochromic switchable films. In this method, an amorphous film of WO3 is produced, and the photocatalytic properties of the WO3 are utilized for the reduction of the Pt2+ precursor to Pt particles. This method also generates a large number of voids in the film at 100 °C. The initial transmittance of the Pt-WO3 films was extremely high (approximately 80%) over the visible to the near infrared region, and the optical change in the transmittance upon exposure to H2 gas or air was large (approximately 70% at a wavelength of 670 nm). In addition, the switching time of the films was as fast as 5 s, and the switching durability of the films was preserved for over 1500 cycles.

Titanium-vanadium dioxide or TixV1−xO2 films for 0 ≤ x ≤ 1 were examined using ellipsometry, and their optical constants (n and k) at visible and near-infrared wavelengths were determined at temperatures (T) below, at, and above the semiconductive-to-metallic phase transition (SMT) temperature (TSM). Ellipsometric analysis was performed for each x at each T using a wavelength dispersion model, i.e., a combination of Lorentz oscillators and a Drude free electron model. The ellipsometric analyses provided information on the electronic band transition caused by the SMT and the influence of cationic replacement (Ti↔V) on the SMT. The results revealed that when x ≤ 0.05, close to the SMT, the energy gap of the interband transition O2p→V3d varied from ≈3.5 eV to ≈3.1 eV, and the quantity of electrons in the interband transition decreased by half. In addition, the energy gap monotonically increased to 4.2 eV when x was increased to 1. Moreover, the energy gap of the split V3d intraband transition varied from ≈1.4 eV to zero, and the quantity of electrons in the intraband transition increased by a factor of four. Furthermore, when x ≥ 0.2, close to the SMT, the energy gap of the intraband transition varied from ≈1.4 eV to a constant positive value, with the generation of a small number of conductive electrons, depending on x.

A new chromogenic nickel oxyhydroxide (NiOOH) thin film was prepared to integrate both its electrochromic and gasochromic characteristics. The NiOOH thin film was obtained using the chemical bath deposition (CBD) method, and was annealed at 300 °C for 2 hours and then subjected to cyclic voltammetry (CV). A palladium catalyst layer was then sputtered onto the NiOOH thin film and the film was prepared for gasochromic application. A large transmittance change (ΔT) was observed, specifically 50.6% at 650 nm and 47.0% at 550 nm, after exposure to hydrogen (H2). The unique memory effects of the chromogenic nickel oxide thin film, which can maintain colour for at least 21 days without significant optical changes, were observed before and after exposure to H2. The bleached film can be switched back to the dark state by applying 0.6 V on the thin film owing to its electrochromic properties. X-ray photoelectron spectroscopy (XPS) analysis was used to confirm the changes in chemical bonding before/after CV treatment and also to confirm that the Pd layer existed on the NiOOH surface. Surface electron microscopy (SEM) images showed highly porous surface morphology after CBD and CV treatment. XRD patterns and FT-IR spectra indicated the structural changes that occurred during film preparation and before/after exposure to H2.

Pd nanoparticles dispersed WO3 (Pd-WO3) gasochromic switchable films were prepared using our method combining UV irradiation and H2 gas flow at room temperature. Structural, chemical and optical switching properties of the films were evaluated and compared with those of the Pt-WO3 films prepared using the same method. It was found that the distribution of catalysts in the Pd-WO3 films was different from that in the Pt-WO3 films. The Pd-WO3 films exhibited large difference in optical transmittance in their colored and bleached states, which was similar to that of the Pt-WO3 films. However, the coloring of the Pd-WO3 films by H2 gas was a little slower than that of the Pt-WO3 films, although the bleaching of these films by air was similarly fast. It was speculated that the difference in the gasochromic properties between the Pd-WO3 and the Pt-WO3 films is likely due to the difference in the distributions of catalysts between the Pd-WO3 and the Pt-WO3 films.

A high-quality gasochromic (GC) platinum nanoparticle/Prussian blue (PtNP/PB) nanocomposite film was produced for the first time by roll-to-roll (R2R) production for high-throughput processing. Wettability was improved when a small amount of hydroxypropyl cellulose (HPC) was mixed with the PB ink, as confirmed by the decrease in the contact angle from 70.9° to 51.7°. SEM images revealed a significant difference between spin and R2R coating methods and also recognized the change in the morphology due to the HPC polymers. However, because of the non-conductive property of the HPC additive, the PB film resistance and GC performance and stability were also affected by the amount of HPC in the film. The analyses of these characteristics and long-term film stability for 1000 cycles were conducted through in-situ UV–visible spectroscopy and electrochemical cyclic voltammetry.

To improve the transmittance of Mg–Y based switchable mirrors in the transparent state the surface was coated with a TiO2 thin film using e-beam evaporation and the optical properties were studied. The TiO2 films had a refractive index of ~2.1. As a result of the TiO2 coating with a thickness of ~65 nm, the transmittance in the visible range was considerably improved and consequently the visible transmittance in the transparent state reached 68%. This result was consistent with simulation results calculated using complex refractive indices for hydrides of Pd, Mg–Y alloy, and Ta. Thus, it is concluded that TiO2 is one of the best candidates for an antireflection layer to improve the optical properties of switchable mirrors.

We report the first observation of gasochromism for a material based on a thin film of polyaniline:polystyrene sulfonate/platinum nanoparticles (PANI:PSS/PtNPs). This novel material displayed a significant colour change, from green to pale yellow, when exposed to hydrogen. Our results show that the PtNPs trigger a reductive reaction on the polymer surface. This new mechanism dramatically expands the selection of available gasochromic materials.

Switchable mirrors are promising materials for energy-saving windows. They are switched between their reflective and transparent states by hydrogenation and dehydrogenation. We have developed gasochromic and electrochromic (EC) switchable mirrors which contain a ternary Mg–Zr–Ni alloy instead of a binary Mg-based alloy, such as Mg–Ni, Mg–Ti, or Mg–Ca. The additional elements in the Mg alloys improve the optical switching properties, and hydrogen-permeable Zr–Ni alloy membranes do not become embrittled by hydrogen and have a high hydrogen permeation rate. Both types of switchable mirror with the Mg–Zr–Ni thin film exhibited optical switching properties, which depended strongly on the composition of the thin film. In both the gasochromic and EC mirrors the switching speed increased as the zirconium and nickel content of the film was increased, although the maximum transmittance decreased. The environmental durability of the EC mirror was investigated using a thermostat/humidistat bath. The durability increased with the zirconium and nickel content of the alloy thin film, and films with a high magnesium content degraded more rapidly.

Pd-capped magnesium–yttrium alloy switchable mirrors were found to have high switching durability of over 10,000 cycles between reflective and transparent states. However, the durability decreased with the decreasing Pd thickness. Switchable mirrors with various Pd thicknesses were then prepared by a direct-current magnetron sputtering method, and the degradation in durability was studied by observing the distribution of each element of the switchable mirrors from the film surface to the substrate. X-ray photoemission spectroscopy and transmission electron microscopy showed that Pd with a short sputtering time (corresponding to layer thickness of 3 nm) resulted in surface oxidation of Mg and Y, and no Pd was present at the surface. The deposited Pd was alloyed with the Mg–Y layer and after taking the sample out from the vacuum chamber a Pd-rich layer appeared between the surface oxides and the Mg–Y layers. With increasing deposition time, a Pd layer was formed on the oxide layer and the Pd layer thickness increased. The mirror with switching durability of over 10,000 cycles had a sufficiently thick Pd top layer of ~7 nm and a very thin oxide layer. This thick Pd layer is believed to be the reason for the high switching durability.

We have synthesized F-doped Ti x V 1−x O2 nanoparticles by hydrothermal method and examined the structural phase transition behavior depending on the Ti and F contents. Differential scanning calorimetry and temperature-dependent X-ray diffraction analyses revealed that, by the codoping of Ti and F in VO2, both the critical phase transition temperature (Tc) and the thermal hysteresis width ( Δ T c ) are appropriately reduced. We have also examined the thermochromic behavior for the composite films prepared by casting F-doped Ti x V 1−x O2 nanoparticles. The 2.0% F-doped Ti 0.08 V 0.92 O2 composite film exhibited a decreased Tc of approximately 20 °C and narrow Δ T c of below 2 °C. This result clearly shows the potential of F-doped Ti x V 1−x O2 nanoparticles for sensitive optical device application.

Switchable mirrors based on magnesium–yttrium alloy thin films were prepared using a direct-current magnetron sputtering method. The optical switching durability between reflective and transparent states using a gasochromic method has been investigated. Pd-capped Mg1−zYz (0.14 0.5. The mirrors with the Y composition in the wide range of 0.27–0.70 have visible transmittance values of about 35% in the transparent state. The difference in visible transmittance between the reflective and transparent states decreased with z, especially over 0.7. In the transparent state, all prepared switchable mirrors had relatively flat optical transmittance spectra in the visible range and showed nearly neutral color appearance. Thus, the optimal Y composition is in the range of 0.5–0.7 for switchable mirrors with high switching durability and large dynamic range between the reflective and transparent states.

Electrochromic switchable mirror glass is promising for energy-saving windows because it changes between a reflective and a transparent state when a voltage is applied. In our previous work, we confirmed that the device degraded at high temperatures and high relative humidity using an accelerated degradation test. The degradation was related to the reaction of the moisture in atmosphere with the surface optical switching layer of the Mg–Ni thin film. Therefore, we have developed a device with a Si incorporated diamond-like carbon thin film surface layer to improve the environmental durability. When the device was kept in a simulated environment at a constant temperature of 40 °C and a constant relative humidity of 60%, optical and atomic force microscopy showed that the surface did not degrade. Moreover, the surface coating repelled water, which prevented the reaction of the moisture with the Mg–Ni thin film. The optical switching speed from the transparent state to the reflective state of the device was slower than that of the uncoated device because of the fabrication conditions. The result seems to be related to the surface of the Mg–Ni layer which might be damaged by the conditions.

Electrochromic switchable mirrors can be reversibly changed between a reflective state and a transparent state by applying a voltage. In our previous work, the properties of the device were significantly affected by environmental factors such as temperature and relative humidity. In that work, the effects on the device properties were investigated through an accelerated degradation test in a thermostat/humidistat bath at a constant temperature of 40 °C and a relative humidity of 80%. The switching speed between the reflective state and transparent state increased as the duration of the simulated environmental exposure increased. The device stored for 7 days under the simulated environmental conditions showed a around 45-fold slower switching speed than that of the as-prepared device. In this work, a high-durability surface coating material constructed from a cyclo olefin polymer sheet and ultraviolet resin was developed to protect the device from environmental degradation. The device with surface coating kept under the simulated environmental conditions for 7 days showed almost the same switching speed as the as-prepared device with the surface coating.

Electrochromic switchable mirrors are expected to be used in energy-saving windows because their optical properties can be changed by application of a voltage. For practical use, the negative impact of environmental conditions on the optical switching properties of the device should be minimized. In this work, the durability of an electrochromic device was investigated in a thermostat/humidistat chamber at −5 °C. After devices were stored at sub-zero temperatures, the switching speed and maximum transmittance decreased only slightly with increasing exposure time. In other words, degradation of the device did not significantly occur at sub-zero temperatures. In comparison, the optical switching properties of a device stored at 40 °C and 60% relative humidity severely deteriorated. This deterioration was attributed to the degradation of the surface of the Mg 4 Ni optical switching layer. This layer was affected by the environmental conditions, and in particular changed from the metallic magnesium state to a non-metallic state. In future work, we will investigate suitable measures for preventing environmental damage to the device.

An electrochromic switchable mirror can be switched between reflective and transparent states by applying voltage. This device can potentially be applied in new energy-saving windows because its reflective state can effectively control incoming solar radiation. We previously evaluated the effects of environmental factors such as temperature and humidity on the optical switching properties of the device using a thermostat/humidistat bath to realize its practical applications. In this work, we focused on the effect of relative humidity in the atmosphere on the properties of the device. When the device was stored at 50 °C and 80% relative humidity (RH) for 15 days, its surface became much rougher ( R a =23.2 nm) as a result of the degradation of the Mg 4 Ni thin film on the surface. The degraded device showed no optical switching properties. On the other hand, when the device was stored at 50 °C and 30% RH for 15 days, its surface was barely degraded and the device showed clear optical switching properties. These results suggest that not high temperature but rather high relative humidity in the atmosphere strongly affect the properties of the device, resulting in surface degradation. A protective coating layer using a fluorocarbon polymer was also developed to prevent the degradation of the device in the environment.

The dehydrogenation process of hydrogenated switchable mirrors using magnesium–nickel alloy thin film was studied in situ using spectroscopic ellipsometry. Ellipsometric angles Ψ and Δ of the switchable mirrors varied drastically as a result of dehydrogenation, which is a transformation from transparent to reflective states. The process was analyzed by dividing into the following three phases. The first phase was the dehydrogenation process of a thin Mg 4 Ni layer with several nanometers at a hydrogenated Pd/Mg 4 Ni interface. The second phase was the dehydrogenation processes of the hydrogenated Mg 4 Ni layer, which proceeded from the Pd/Mg 4 Ni interface to the substrate. The final phase was the desorption process of hydrogen, which was absorbed in Mg 4 Ni as solid solution and the dehydrogenation process was terminated.

We investigate the self-organized growth of short TiO 2 nanotubes by complete anodization of Ti thin films deposited on Si substrates in ethylene glycol electrolytes with small addition of NH 4 F. During the anodization process, real-time inspection of the current transient is performed to anodize the Ti films completely. X-ray photoelectron spectroscopy and scanning electron microscopy are employed to characterize the resulting samples. We find that the length of the formed TiO 2 nanotubes is governed by the thickness of Ti thin films independently of the tube diameter. Short TiO 2 nanotubes are also found to be stable up to 550 °C in air atmosphere even after crystallization to rutile.

Mg–Ni thin films as a switchable mirror material are promising for application in energy-saving windows because they can change their state between reflective and transparent by hydrogenation and dehydrogenation. In our previous work, we found that electrochromic switchable mirror glass based on a Mg4Ni thin film is affected by environmental factors such as temperature and humidity. In this work, we investigated the effects of the environment on the optical switching properties of electrochromic switchable mirrors with Mg–Ni thin films of various compositions suitable for a broad range of applications and operating environments. When the mirror devices were kept in a simulated environment with a constant temperature 40 °C and a constant relative humidity of 80%, controlled by a thermostat/humidistat bath, their optical switching properties degraded. The degradation was found to be related to the change in the Mg–Ni thin films into nonmetallic states of oxides and hydroxides. The device with a Mg6Ni thin film kept in the bath for 7 days showed no optical switching property. The mechanism of degradation in the bath was strongly affected by the composition of the Mg–Ni thin-film optical switching layer. The device constructed with an optical switching layer having high magnesium content degraded more rapidly in the test.

Electrochromic switchable mirrors consisting of a multilayer of Mg 4 Ni/Pd/Al/Ta 2 O 5 /H X WO 3 /indium tin oxide on a glass substrate degrade when subjected to changes in humidity and temperature. Polyvinyl chloride was applied as a seal layer to such a device in an attempt to improve its durability. The optical switching properties of the device were investigated through an accelerated degradation test conducted at a constant temperature of 30 °C and a relative humidity of 80%. Although the device with a seal layer was thicker, it showed superior optical switching properties with a transmittance as high as 54% in the transparent state due to interference at the multilayer. Furthermore, the device with a seal layer exhibited higher durability after 35 days in an accelerated degradation environment, as well as higher switching durability.

We have developed an electrochromic switchable mirror foil with a structure of Mg4Ni/Pd/Al/Ta2O5/HXWO3/indium tin oxide on a polyethylene terephthalate (PET) substrate. When a voltage is applied to the device, the protons in the WO3 layer move to the Mg4Ni layer, which is then hydrogenated to form MgH2 and Mg2NiH4. The hydrides have higher transparency, and thus the device can be effectively switched to a transparent state. We have previously reported a process where the device was fabricated by using a sulfuric acid solution to introduce protons to the WO3 layer. However, the solution-based process appeared to have low adaptability to commercial processes. In the present work, we focused on fabricating the device by only solid-state processing. Specifically, a hydrogen-containing solid electrolyte layer of Ta2O5 thin film was fabricated by reactive dc magnetron sputtering in a mixture gas of argon, oxygen and hydrogen. We optimized the fabrication conditions of the hydrogen-containing Ta2O5 thin film for the device. In comparison with the device fabricated by the solution-based process, the device fabricated by only the solid-state process was more durable, retaining its optical switching properties for 7 days at a temperature of 40 °C and relative humidity of 80%. This result was related to the prevention of degradation on the surface of the Mg4Ni thin film.

Optical switching processes of Mg-Ni based switchable mirrors were studied "in situ" using spectroscopic ellipsometry. Ellipsometric angles psi and Delta of the switchable mirrors varied drasticall ...

We have been engaged in research and development of an electrochromic switchable mirror with a multilayer structure of Mg4Ni/Pd/Al/Ta2O5/HXWO3/indium tin oxide (ITO) on a glass substrate. In our recent work, an as-prepared device was found to be easily degraded by environmental factors such as temperature and humidity, as shown by a degraded surface of the device. In this work, a polyvinyl chloride (PVC) layer was fabricated as a sealant layer for improving the environmental durability of the device. The structure of the layer could be controlled by adjusting the fabrication conditions such as the concentration of materials and rotational speed used in spin coating. The optical switching properties of the device with the sealant layer were also investigated. The sealant layer was fabricated using 1.25 wt % PVC solution in tetrahydrofuran at a rotational speed of 500 rpm. Although the device with the sealant layer had a thicker film, it showed superior optical switching properties even with a change in reflectance range due to multilayer interference. Furthermore, the device without the sealant layer easily degraded in an accelerated degradation test at a constant temperature of 40°C and a constant relative humidity of 80% after only 2 days. On the other hand, the surface of the device with the sealant layer showed no change in the same test. This result suggests that the PVC sealant layer has some advantages for preventing the environmental effects on the properties of the device.

With the capability to change between reflective and transparent states, electrochromic switchable mirrors are expected to have numerous applications in optical devices, electronics devices and new energy-saving windows. If conventional windows can be adapted to incorporate switchable mirror technology, the solar radiation coming into a room could be effectively controlled, owing to features of the reflective state. Conventional windows are often subjected to environmental conditions such as high temperature and humidity. Considering practical use, we investigated the effects of the environment on the optical switching properties of the device in accelerated degradation tests using a thermostat/ humidistat bath at a constant temperature of 313 K and constant relative humidity of 80%. When the device was kept in the bath for 950.4 ks, it lost its optical switching properties. This result was associated with the degradation of the surface layer of the Mg4Ni thin film, which became rougher with increasing bath duration. We confirmed that the layer contained species in non-metallic states of oxide and hydroxide. Furthermore, the degradation mechanism to form the mixture state depended on the holding time in the bath. [doi:10.2320/matertrans.MBW201010]

We investigated the fabrication conditions of a solid electrolyte Ta2O5 thin film suitable for an electrochromic (EC) all-solid-state switchable mirror glass to reduce material and processing costs. The film was deposited by reactive dc magnetron sputtering in a mixture gas of argon and oxygen. The electrochemical properties of the film on a WO3/ITO/glass substrate and the optical switching properties of the EC switchable mirror device were investigated, considering the thickness of the Ta2O5 thin film. All the films on WO3/ITO/glass substrates in this work exhibited similar current density, as measured by cyclic voltammetry. The electrochemical properties of the film with thickness reduced by 75% were almost the same as those of the conventional film. However, the device constructed with the thinner film displayed poor optical switching properties. Switching from the reflective state to the transparent state upon application of a voltage, the device with a 100-nm-thick film required a switching time that was 3 times longer than that of the conventional device constructed with a 400-nm-thick film. These results indicate that suitable fabrication conditions for the solid electrolyte Ta2O5 thin film of EC all-solid-state switchable mirror glass can potentially be found that reduce consumption of materials and shorten processing time.

To improve the visible transmittance of switchable mirrors based on Mg–Y alloys in the transparent state using antireflection layers, optical indices n and κ of the hydrogenated switchable mirrors were evaluated using spectroscopic ellipsometry in the range of 310 to 1650 nm. The Y composition z in the Mg1 − zYz alloys was varied between 0.51 and 0.7. The evaluated spectra both n and κ in the visible range increased with decreasing wavelength and increasing Y composition. Furthermore, the wavelength where the k value increased sharply was increased with Y composition. As a result of estimation of the effect of antireflection (AR) coating, it is expected that a switchable mirror using Mg0.39Y0.61 covered with AR layer with the refractive index of ~ 2.3 and ~ 50 nm thickness improved to be Tvis of over 60%, while the switchable mirror without AR had Tvis of 34%. Thus, it is concluded that AR layer is effective to improve Tvis in the transparent state.

We have developed an electrochromic switchable mirror that consists of all-solid-state thin films. The device can be switched between reflective and transparent states by applying a voltage. This device can potentially be applied to new energy-saving windows because the reflective state of the mirror can effectively control the solar radiation coming into a room. To realize such practical applications, the effects of environmental factors such as temperature and humidity on the optical switching properties of the device should be investigated in detail. In this work, we evaluated the effects of the environment on the device for various constant temperature and relative humidity conditions, which were controlled by a thermostat/humidistat bath. When the device was stored at 50 °C and 80% relative humidity (RH) for only 7 days, its surface became much rougher (Ra=21.9 nm) as a result of degradation of the Mg4Ni thin film on the surface. Moreover, the degraded device lost its optical switching properties. The device was strongly affected by high temperatures and high relative humidity in the atmosphere, resulting in rapid degradation. To address this problem, a device with a protective surface layer was also fabricated, and its durability was evaluated by the same method. The device with the protective layer was found to retain its optical switching properties under a harsh environment.

An electrochromic (EC) switchable mirror glass can change between a reflective state and a transparent state with voltage application. The conventional device has a multilayer of Mg4Ni/Pd/Al/Ta2O5/WO3/indium-tin oxide on a transparent substrate. A palladium thin film was used as the proton injection layer. For practical use, we attempted to reduce the amount of palladium thin film from the viewpoints of the reduction in total fabrication cost and the efficient use of resources. The thickness of the film was related to the optical switching properties of the device. Although the device with a 1-nm-thick palladium film showed a high transmittance of 63% in the transparent state, its low switching durability was not suitable for practical application. Moreover, we were able to adapt a palladium-based alloy (Pd0.8Ag0.2) which is a well-known hydrogen permeation membrane as the proton injection layer to reduce the amount of palladium thin film. As a result, we found that a 4-nm-thick Pd–Ag thin film has good adaptability to the EC switchable mirror.

Electrochromic switchable mirror glass is expected to be implemented in new energy-saving windows, as it can switch between reflective and transparent states simply through an applied voltage. In its reflective state, it can effectively control the solar radiation coming into a room. However, conventional windows are often affected by environmental factors such as temperature and humidity. In this work, we investigated the effects of the environment on the optical switching properties of the mirror. In accelerated degradation studies, when the mirror was kept in a simulated environment with high temperature and high relative humidity controlled by a thermostat/humidistat bath, its optical switching properties degraded. After being kept for 34 days at a temperature of 30 °C and a relative humidity of 80%, the mirror never showed its optical switching property. Moreover surface roughness increased up to Ra=13.1 nm, due to the degradation of the surface layer of the Mg4Ni thin film. The layer changed into a non-metallic state of oxide and hydroxide, as determined by the X-ray photoelectron microscopy. We confirmed that the mirror was significantly affected by the environment, especially by high relative humidity in the atmosphere, which caused rapid degradation of the mirror.

An electrochromic switchable mirror on a flexible plastic sheet was developed taking into consideration practical use, low cost and high adaptability. The mirror has a multilayer of Mg 4 Ni/Pd/Al/Ta 2 O 5 /WO 3 , which was fabricated by DC magnetron sputtering on an ITO-coated PET sheet. In the previous research, when the mirror was exposed to air for a long period of time, its optical switching properties disappeared. This work focused on the mechanism of degradation of the mirror in different environments. When the mirror was stored in a desiccator for 50 days as a means of preservation, its switching speed was seven times higher as compared with the mirror exposed to air. It is also well known that oxygen and moisture in air easily penetrate PET sheets. The features of the PET sheet strongly affected the durability of the optical switching layer. When the state of the optical switching layer was changed to nonmetallic due to the formation of oxide and hydroxide, the optical switching properties almost disappeared.

An all-solid-state switchable mirror glass can change between its reflective (mirror) and transparent states by the use of an applied voltage. New energy-saving windows are expected to be one of the possible applications of the proposed device that utilizes this state change. In practical use, conventional windows are warmed by solar radiation of heat. Therefore, here we investigated the effects of temperature on the optical switching properties of the device. Although higher temperature increased the switching speed of the device, degradation occurred more rapidly. This result seemed to be related to the proton conductivity of the solid electrolyte layer of Ta2O5. We confirmed the relationship between temperature and proton conductivity of the layer by the conventional impedance method. We found that higher temperatures resulted in higher proton conductivity of Ta2O5, and at the interface of Pd and Mg4Ni thin films, hydride formation occurred. Hydride appeared to prevent the diffusion of protons into the optical switching layer, resulting in imperfect switching.

The hydrogenation and dehydrogenation switching processes of Pd thin films were analyzed by measuring in situ in real time the variation in ellipsometric Ψ and Δ during hydrogenation and dehydrogenation using spectroscopic ellipsometry. The hydrogenation proceeded from the film surface and a mixture layer of metal and hydride was formed at the surface. With time elapse, the thickness of the mixture layer increased rapidly. After the whole Pd metal layer transformed to the mixture layer, the concentration of hydride in the mixture layer increased. Finally, the concentration reached 1; the whole Pd in the mixture layer was hydrogenated, and the hydrogenation of Pd was complete. On the other hand, the dehydrogenation proceeded in a way completely opposite to the hydrogenation process; the concentration of hydride in the mixture layer decreased, Pd metal layer was formed at the interface between the film and the substrate, and the whole layer returned to Pd metal. The dehydrogenation proceeds much faster than hydrogenation.

We applied magnesium–titanium (Mg–Ti) thin film as the optical switching layer to all-solid-state switchable mirror on plastic sheet (polyethylene terephthalate, PET) in the viewpoint of clear transparency at the transparent state. For the switching speed from the reflective to the transparent states, the PET-device showed a little slower switching speed than the glass-device, and it depended on the sheet resistance of indium tin oxide (ITO). When Mg–Ti thin film was applied to the PET-device, absorption at the visible ray was reduced, resulting in near-colorless state at the transparent state. The PET-device with Mg–Ti thin film showed chromaticity coordinates of x=0.341 and y=0.339 and a luminous transmittance of 42.4% at the transparent state. However, the PET-device had lower durability than that of the glass-device. It seemed to be related with the degradation mechanism of the optical switching layer. When Mg–Ti thin film after the durability test was analyzed by XPS, though the glass-device had much oxidized state of magnesium, the PET-device had mixture states of oxide and hydroxide in the optical switching layer. We suggest that the hydroxide in the layer will be formed by including water in the PET sheet, and the hydroxide might significantly affect the rapid degradation of the PET-device.

Pd-capped Mg-rich Mg–Ni alloy thin film shows excellent reversible switching properties in optical transmittance by the exposure to hydrogen containing gas. However, it shows fast degradation due to the oxidization of magnesium and the switching durability is not good enough for practical applications. To resolve this problem we tried to improve its switching durability of Mg–Ni based switchable mirror by the combined use of metal buffer layer insertion between Pd and Mg–Ni layer and polytetrafluoroethylene (PTFE) protective coating. PTFE thin film has been prepared on the surface of Mg–Ni thin films by RF magnetron sputtering in the Ar and CF 4 mixed gas discharge plasma at room temperature and a power of 30 W. The sample of Pd/Ti/Mg 4 Ni thin film with the protective coating of 900-nm-thick PTFE layer can be switched over 1600 switching cycles, which suppress the degradation by 15% of its initial transmission modulation level.

We investigated the electrochemical property of Ta 2 O 5 thin film for all-solid-state switchable mirror glass. The film was deposited by reactive dc magnetron sputtering in a mixture gas of argon and oxygen. The current density of the film covered WO 3 /ITO/glass was decreased with decreasing argon/oxygen ratio and working pressure measured by cyclic voltammetry. The film deposited at argon/oxygen ratio of 4.7 and working pressure of 1.0 Pa had better electrochemical property than that of other deposition condition. Its estimated proton conductivity was 2.1 × 10 − 9 S/cm by conventional ac impedance method. However, the device using the film showed poor optical switching property. The transmittance change of the device at a wavelength of 670 nm was only 16% by applying voltage. On the other hand, the device using the film deposited at working pressure of 0.7 Pa was able to switch its optical switching property from reflective of 0.1% to transparent states of 44% within 15 s. These results indicate that the suitable deposition condition of the Ta 2 O 5 thin film existed to be used for all-solid-state switchable mirror glass.

To examine the antidazzle effect of switchable mirrors, mirrors based on a magnesium–nickel alloy were prepared on three kinds of transparent substrates with different surface roughness. The mirrors prepared using a direct-current magnetron sputtering method have nearly the same surface morphology and roughness as the underlying substrates. The diffuse fraction of the total reflectance of the mirrors increases with surface roughness of the mirrors. Thus, by utilizing substrates with rough surfaces, the specular reflectance of the mirrors decreases and consequently it is possible to prepare switchable mirrors with an antidazzle effect.

In this work, we produced a switchable mirror thin film based on a Mg4Ni thin film with a Pd top layer deposited on transparent polymer sheets. The Mg4Ni thin film was prepared on poly(ethylene naphthalate) and poly(ethylene terephthalate) substrates by the DC magnetron cosputtering of Mg and Ni targets followed by in situ covering with a Pd thin layer. The gasochromic switching properties, durability, and response (hydrogenation and dehydrogenation kinetics) were investigated by loading 4% hydrogen in Ar. We found that Pd/Mg4Ni thin film mirrors on a poly(ethylene naphthalate) sheet have superior switching properties. The hydrogenation time (transition from the metallic state to the transparent state) of the sample is almost the same as the hydrogenation time of the same sample prepared on a glass substrate, whereas the dehydrogenation time (transition from the transparent state to the metallic state) is shorter than that of the glass substrate sample. In addition, the switching durability of the sample on the flexible sheet is extended to 200 switching cycles. These results show that the switchable mirror deposited on flexible sheets has a similar performance to the sample on glass substrates.

We have developed an all-solid-state switchable mirror of Mg4Ni/Pd/Ta2O5/WO3/ITO on glass. Each material of Mg4Ni, Pd, and Ta2O5 in the device acts as an optical switching, a proton injector and a solid electrolyte, respectively. The initial state of the device is a reflective state as a mirror and the state changes to a transparent one by applying voltage. In this work, solid electrolyte of Ta2O5 thin film was deposited on the WO3/ITO/glass substrate by reactive DC magnetron sputtering with Ar/O2 mixture gases. The effect of Ar/O2 ratio on the electrochemical property of Ta2O5 thin film and the optical switching property of the device were investigated. The film deposited at Ar/O2 of 4.7 had better electrochemical property than that of other films. The transmittance at a wavelength of 670 nm of the device using Ta2O5 thin film deposited at Ar/O2 of 4.7 was reached from the reflective state of 0.1% to the transparent state of 44% less than 15 s by applying voltage of 5 V. The device showed a stable durability of up to 1000 switching cycles.

We are developing switchable mirror thin films based on an Mg–Ni alloy which can be switched between mirror and transparent states. The Mg4Ni alloy thin film was prepared on a glass substrate by DC magnetron co-sputtering of Mg and Ni targets and was subsequently covered in situ with a thin layer of Pd. The interface structure between Pd and Mg–Ni layers was found to have a crucial effect on the switching response and durability. By controlling the sputtering sequence and tailoring the interface structure, the switching response can be improved by 50–80% for the dehydrogenation process. The switching durability of the improved thin film is twice as long as that of a typical sample. We have also found that the switching response is dependent on the substrate temperature during sputtering. The dehydrogenation rate can be increased when the substrate is retained below room temperature.

ARTICLE I NFO The all-solid-state switchable mirror based on magnesium-nickel thin film was fabricated on the flexible sheet of polyethylene terephthalate (PET) to reduce process cost and make handling easy for practical application of smart window. The device has the multilayer of Mg4Ni/Pd/Al/Ta2O5/HXWO3/indium tin oxide (ITO) on PET sheet. Each material of the Mg4Ni, Pd, Al, Ta2O5 ,H XWO3 and ITO layers in the device work as an optical switching layer, a proton injector, a buffer layer, a solid electrolyte, an ion storage layer and a transparent conductor, respectively. The effect of the sheet resistance of ITO on the optical switching property of the device was investigated. The optical switching speed of the device on the PET sheet became fast decreasing with the sheet resistance of ITO. The device on the PET sheet with the lower sheet resistance of 35 Ω/sq of ITO showed faster switching speed of 10 s from the reflective state to the transparent one and higher durability than those of the device with other sheet resistances. We expect that the device with lower sheet resistance of ITO made better switching property in the view point of low power consumption operation.

Tungsten oxide thin films with protons intercalated during deposition (Hx WO3) were prepared using reactive direct-current magnetron sputtering in a gas mixture of argon, oxy-gen, and hydrogen. The as-deposited films were tungsten bronze. The concentration of intercalated protons, given by the x -values in Hx WO3, was evaluated by electrochemically ejecting protons from the films. The x -value was proportional to the hydrogen flow ratio at the deposition. The dispersion of the extinction coefficient (κ) of the films was estimated by analyzing the experimental spectra measured with spectroscopic ellipsometry using the model composed of a homogeneous tungsten bronze layer with an additional surface roughness layer. As a result of this analysis, the κ -value increases strongly with intercalated protons, and a linear dependence existed between the x -value and κ -value. Therefore, it is possible to evaluate the x -value of the Hx WO3 films using this dependence without ejecting protons. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thin buffer layers of hydrogen diffusive metals such as Ti, Nb, and V were inserted between a Mg4Ni thin film and a Pd top layer, which were prepared by DC magnetron sputtering. Their optical, electrochemical properties, and switching durability were investigated using both gasochromic and electrochromic switching methods. It has been proved that Ti, Nb, and V buffer layers can protect the migration of Mg to surface of thin film during the switching processes, and also service as a protection layer against the oxidization of Mg. These metal buffer layers do not affect the hydrogenation of Mg–Ni alloy mirrors system when switching with hydrogen gas or electrochromic, rather, its dehydrogenation speed is accelerated greatly. Switching cyclic number of those metal buffer layer inserted mirrors achieved 400–500 cycles which was enhanced ca. 3 times than non-inserted one.