Characterization of flexible switchable mirror film prepared by DC magnetron sputtering

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 Mg₄Ni/Pd/Al/Ta₂O₅/WO₃, 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.     

Characterization of flexible switchable mirror film prepared by DC magnetron sputtering

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 Mg₄Ni/Pd/Al/Ta₂O₅/WO₃, 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.     

Null-ellipsometry investigations of the optical properties and diffusion processes in spin-valve structures based on Co and Cu

The influence of annealing temperature (T_a = 300-900 K) on optical properties of the Au (4 nm)/Co (3 nm)/Cu (6-12 nm)/Co (20 nm)/SiO₂/Si spin-valve structures was studied. The model of Co, Au, and Cu atom interdiffusion was proposed based on the experimental data analysis. The formation of solid solutions at the thin layer interfaces Au/Co and Cu/Co was studied, and as a result the most intensive formation of solid solutions was identified at annealing temperature of T_a = 750 K. The optical parameters of the samples were calculated using the genetic algorithm. The spin-valve systems remain relatively unperturbed until 750 K, but the optical properties change significantly from 750 to 900 K. It can be explained by the formation of the interphase in multilayer thin film systems.     

Reactive DC sputter-deposited tantalum oxide thin film for all-solid-state switchable mirror

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.     

ZnO/Cu/ZnO multilayer films: Structure optimization and investigation on photoelectric properties

A series of ZnO/Cu/ZnO multilayer films has been fabricated from zinc and copper metallic targets by simultaneous RF and DC magnetron sputtering. Numerical simulation of the optical properties of the multilayer films has been carried out in order to guide the experimental work. The influences of the ZnO and Cu layer thicknesses, and of O₂/Ar ratio on the photoelectric and structural properties of the films were investigated. The optical and electrical properties of the multilayers were studied by optical spectrometry and four point probe measurements, respectively. The structural properties were investigated using X-ray diffraction. The performance of the multilayers as transparent conducting coatings was compared using a figure of merit. In experiments, the thickness of the ZnO layers was varied between 4 and 70 nm and those of Cu were between 8 and 37 nm. The O₂/Ar ratios range from 1:5 to 2:1. Low sheet resistance and high transmittance were obtained when the film was prepared using an O₂/Ar ratio of 1:4 and a thickness of ZnO (60 nm)/Cu (15 nm)/ZnO (60 nm).     

Characterization and humidity sensing of ZnO/42° YX LiTaO3 Love wave devices with ZnO nanorods

Love mode surface acoustic wave devices based on ZnO/42° YX LiTaO₃ were characterized with the thickness of the sputtered ZnO guiding layer varied from 250 nm to 1.18 μm. Phase velocity, temperature coefficient of resonant frequency, sensitivity, electromechanical coupling coefficient and humidity sensing of the Love mode SAW devices were studied as a function of the ZnO layer thickness. With increasing ZnO thickness over the range of thickness values we have examined, the sensitivity of 42° YX LiTaO₃ to liquid loading increased and the values of electromechanical coupling coefficient decreased. The device with a thickness of 250 nm showed the best humidity response. ZnO nanorods were grown on this device and its humidity sensing performance has been further improved due to their large surface-to-volume ratio of the ZnO nanorods.     

Prediction of environmental degradation of closed adhesive joints using data from open-faced specimens

A framework was established to predict the fracture toughness of degraded closed DCB (CDCB) joints of a toughened adhesive-aluminum system using fracture data obtained from accelerated degradation tests on open-faced joints. The exposure index (EI), the time integral of water concentration, was calculated at all points in the closed joints using the water diffusion properties of the adhesive. The fracture toughness of the closed joints was then predicted from these calculated EIs by making reference to previously reported fracture toughness data from open-faced DCB (ODCB) specimens degraded to various EI levels. To verify the predictions, fracture experiments and analyses were carried out for closed DCB joints degraded at 60 °C-95% relative humidity (RH) and 60 °C-82% RH conditions. The failure mode of both closed and open DCBs was cohesive in the adhesive layer. Good agreement was observed between the predicted steady-state critical strain energy release rate (G_cs) values and the experimentally measured G_cs values for the degraded closed DCB joints. The results showed that the accelerated open-faced methodology, which significantly reduces the exposure time to reach a given level of degradation, can be used to predict the durability of degraded closed joints used in service conditions. It was also shown that at a given temperature, the knowledge of the degradation behavior at one RH level could be extended to other levels of RH with an acceptable accuracy using the fact that fracture degradation at a given temperature is a unique function of EI, independent of the RH exposure history that gives rise to EI. The results are applicable to other laminated systems where degradation of the bonding layer is a failure mode of concern.     

Water permeation through organic-inorganic multilayer thin films

We prepared organic (self-assembled monolayer (SAM))-inorganic (TiO₂) multilayer barrier films on polyethylene terephthalate substrate using atomic layer deposition and molecular layer deposition methods in the same deposition chamber. The water permeation was mainly blocked by the inorganic TiO₂ layer. While the lag time was proportional to the thickness of the TiO₂ layer, the steady-state permeation rate was relatively independent of the thickness. The multilayer approach was effective in extending the lag time due to both the tortuous path effect and the internal desiccant effect. Water permeation occurred sequentially in the organic-inorganic multilayer barriers by water accumulation in the organic SAM layers. The water vapor transmission rate was 7.0 × 10^− 4 g/m²·day during the lag time of 155 h at 60 °C and a relative humidity of 85% with 5-dyad barrier film.     

Optical and electrical properties of zinc oxide/indium/zinc oxide multilayer structures

Zinc oxide/indium/zinc oxide multilayer structures have been obtained on glass substrates by magnetron sputtering. The effects of indium thickness on optical and electrical properties of the multilayer structures are investigated. Compared to a single zinc oxide layer, the carrier concentration increases from 8 × 10¹⁸ cm⁻³ to 1.8 × 10²⁰ cm⁻³ and Hall mobility decreases from 10 cm²/v s to 2 cm²/v s for the multilayer structure at 8 nm of indium thickness. With the increase of indium thickness, the transmittance decreases and optical band gap shifts to lower energy in multilayer structures. Results are understood based on Schottky theory, interface scattering mechanism and the absorption of indium layer.     

Improved durability of electrochromic switchable mirror with surface coating in environment

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.     

Nitridation and contrast of B4C/La interfaces and X-ray multilayer optics

Chemical diffusion and interlayer formation in thin layers and at interfaces is of increasing influence in nanoscopic devices such as nano-electronics, magneto-optical storage and multilayer X-ray optics. We show that with the nitridation of reactive B₄C/La interfaces, both the chemical and optical contrast can be greatly enhanced. Although interaction and diffusion of N₂ from the substrate towards the adlayer does occur, this surfactant mediated growth contributes to chemical and optical interface properties that enable major reflectivity improvements of multilayer optics for 6.7 < λ < 7.0 nm.     

Conductive Ga doped ZnO/Cu/Ga doped ZnO thin films prepared by magnetron sputtering at room temperature for flexible electronics

Ga doped ZnO(GZO)/Cu/GZO multilayers were deposited by magnetron sputtering on polycarbonate substrates at room temperature. We investigated the structural, electrical, and optical properties of multilayers at various thicknesses of Cu and GZO layers. The lowest resistivity value of 3.3 × 10^− 5 Ω cm with a carrier concentration of 2.9 × 10²² cm^− 3 was obtained at the optimum Cu (10 nm) and GZO (10 nm) layer thickness. The highest value of figure of merit φ_TC is 2.68 × 10^− 3 Ω^− 1 for the GZO (10 nm)/Cu(10 nm)/GZO(10 nm) multilayer. The highest average near infrared reflectivity in the wavelength range 1000-2500 nm is as high as 70% for the GZO(10 nm)/Cu(10 nm)/GZO(10 nm) multilayer.     

Optical and electrochemical properties of all-solid-state transmittance-type electrochromic devices

Using a vacuum dry process, we constructed an all-solid-state transmittance-type electrochromic (EC) device consisting of five thin layers: ITO/IrO_x/Ta₂O₅/WO₃/ITO. We measured the optical and electrochemical properties of the EC device. By using Ta₂O₅ film as a proton conducting solid electrolyte, the device exhibited a fast response speed of 0.2 s and stable coloration characteristics. With an AC impedance method, we determined the properties of the device under varying temperature and environmental conditions. In the solid electrolyte (Ta₂O₅), the ion resistance controlled the response speed; the ionic conductivity and activation energy were 3 × 10^− 6 S/cm and 0.31 eV, respectively.     

Deposition of nano-scaled CrTiAlN multilayer coatings with different negative bias voltage on Mg alloy by unbalanced magnetron sputtering

In a magnetron sputtering system, the negative substrate bias voltage has been used as a basic process parameter to modify the deposition structure and properties of coatings. In this paper we report the effect of bias voltage ranging from −40 V to −90 V on nano-scaled CrN/TiN/CrN/AlN (CrTiAlN) multilayer coatings synthesized on a Mg alloy by a closed-field unbalanced magnetron sputtering ion plating system in a gas mixture of Ar + N₂. The technological temperature and atomic concentration in the multilayer coatings were controlled by adjusting the current density of different metal magnetron targets and the plasma optical emission monitor. The composition, crystallographic structure, deposition model and friction coefficient of multilayer coatings were characterized by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ball-on-disc testing. The experimental results show that the deposition model and friction coefficient of nano-scaled CrTiAlN multilayer coatings were significantly affected by the negative bias voltage (V_b). The nitride species in multilayer coatings mainly involve CrN, AlN and TiN, and XRD analysis shows that the crystallographic structure was face-centered cubic. Under different bias voltage conditions, the multilayer coating composition shows a fluctuation, and the Al and Cr concentrations respond in the opposite sense to the bias voltage, attaining their greatest values at V_b = −70 V. The surface and cross-sectional morphology shows deposition model change from a columnar model into non-columnar model with the increase in negative bias voltage. The friction coefficient of the nano-scaled multilayer coatings at V_b = −55 V stabilize after 10 000 cycles.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Fabrication of TiO2 thin film memristor device using electrohydrodynamic inkjet printing

In this paper, we are reporting the fabrication of memristor device (Ag/TiO₂/Cu) using electrohydrodynamic inkjet printing technology. The titanium oxide (TiO₂) active layer was deposited using electrohydrodynamic atomization technique. The metal electrodes were patterned by using electrohydrodynamic printing technique. The crystalline nature, surface morphology and optical properties of as deposited TiO₂ films were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-visible spectroscopic analysis respectively. XRD and SEM studies revealed that the presence of anatase TiO₂ with uniform deposition. The optical transmittance of the deposited TiO₂ films was observed to be 87% in the visible region. The fabricated memristor device (Ag/TiO₂/Cu) exhibits bipolar resistive switching behavior within the low operating voltage (± 0.7 V). Our results ensure that the printed technology provides breakthrough solution in the electronic memory device fabrication.     

Electrical and structural properties of Ta-N thin film and Ta/Ta-N multilayer for embedded resistor

Ta/Ta-N multilayer has been developed to control temperature coefficient of resistance (TCR) in a thin-film embedded resistor with the incorporation of Ta layer (+ TCR) inserted into Ta-N layers (− TCR). Electrical and structural properties of sputtered Ta, Ta-N and the multilayer films were investigated. The stable resistivity value of 0.0065 Ω·cm in β-Ta film was obtained, and phase change from fcc-TaN to orthorhombic Ta₃N₅ in Ta-N films was observed at nitrogen partial pressure of 22%. The multilayer of Si/Ta(60 nm)/Ta₃N₅(104 nm)/Ta(60 nm)/Ta₃N₅(104 nm) showed TCR value of − 284 ppm/K, where TCR of Ta was − 183 ppm/K and that of Ta₃N₅ was − 3193 ppm/K.     

Organic photovoltaic cells fabricated on a SnOx/Ag/SnOx multilayer transparent conducting electrode

Transparent conducting multilayer structured electrode of a few nm Ag layer embedded in tin oxide thin film SnO_x/Ag/SnO_x was fabricated on a glass by RF magnetron sputtering at room temperature. The multilayer of the SnO_x(40 nm)/Ag(11 nm)/SnO_x(40 nm) electrode shows the maximum optical transmittance of 87.3% at 550 nm and a quite low electrical resistivity of 6.5 × 10^− 5 Ω cm, and the corresponding figure of merit (T¹⁰/R_S) is equivalent to 3.6 × 10^− 2 Ω^− 1. A normal organic photovoltaic (OPV) structure of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/polythiophene:phenyl-C60-butyric acid methyl ester/Al was fabricated on glass/SnO_x/Ag/SnO_x to examine the compatibility of OPV as a transparent conducting electrode. Measured characteristic values of open circuit voltage of 0.62 V, saturation current of 8.11 mA/cm² and fill factor of 0.54 are analogous to 0.63 V, 8.37 mA/cm² and 0.58 of OPV on commercial glass/indium tin oxide (ITO) respectively. A resultant power conversion efficiency of 2.7% is also very comparable with the 3.09% of the same OPV structure on the commercial ITO glass as a reference, and which reveals that SnO_x/Ag/SnO_x can be appropriate to OPV solar cells as a sound transparent conducting electrode.     

Structural, electrical and optical properties of ITO films with a thin TiO2 seed layer prepared by RF magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited by RF magnetron sputtering on TiO₂-coated glass substrates (the TiO₂ layer is usually called seed layer). The properties of ITO films prepared at a substrate temperature of 300 °C on bare and TiO₂-coated glass substrates have been analyzed by using X-ray diffraction, atomic force microscope, optical and electrical measurements. Comparing with single layer ITO film, the ITO film with a TiO₂ seed layer of 2 nm has a remarkable 41.2% decrease in resistivity and similar optical transmittance. The glass/TiO₂ (2 nm)/ITO film achieved shows a resistivity of 3.37 × 10⁻⁴ Ω cm and an average transmittance of 93.1% in the visible range. The glass/TiO₂ may be a better substrate compared with bare glass for depositing high quality ITO films.