Preparation conditions of sputtered electrochromic WO3 films and their infrared absorption spectra

Tungsten oxide films were prepared by rf sputtering in an argon-oxygen atmosphere from W and WO₃ targets. To bring about reversible electrochromic (EC) characteristics, as-deposited films require an aging process (i.e. cycles of injection/ejection of charge carriers). The infrared absorption band at around 3300 cm⁻¹ increases during the aging process, and it is assigned as OH stretching vibrations of absorbed water.By coloration after aging, the 3300 cm⁻¹ band decreases, and a new band appears at 2400 cm ⁻¹. The latter band is considered to be to the stretching mode of radicals incorporated in the WO₃ matrix. At low coloration levels, the 2400 cm⁻¹ band increases slightly with injected charge, and a coloration mechanism other than the usual double injection model may be considered.The coloration efficiency depends on the preparation conditions. Its maximum value is the same for films prepared from W and WO₃ targets, and is 60 cm²/C at a wavelength of 600 nm. When a tungsten target is used, the substrate temperature is low and the deposition rate is high compared with a WO₃ target.     

Electrochromism of Li-intercalated Sn oxide films made by sputtering

Sn oxide films were made by reactive rf magnetron sputtering under conditions that led to both electronic and ionic conductivity. Li⁺ intercalation produced electrochromism with coloration efficiency peaked in the infrared.     

Residual charges and infrared absorption in electrochromic WO3 films prepared by hydrogen-introduced sputtering

Electrochromic WO₃ films were prepared by rf−sputtering in atmosphere consisting of Ar/H₂/O₂ mixed gas. The as-sputtered films require several times of injection/extraction of ions (the aging) for obtaining reversible coloration/bleaching. After the aging, there are ions (protons) remaining in the films, namely residual charges. From the results of IR absorption of the as-sputtered and aged films, the residual charges contribute to create OH and HOH bonds. Hydrogen introduced in the films during sputtering is transformed only into OH bonds combining with unstable oxygen in the films. The introduced hydrogen is considered to suppress the growth of grain in WO₃ films from AFM observation.     

Optically passive counter electrodes for electrochromic devices: transition metal–cerium oxide thin films

Films of W–Ce oxide and Ti–Ce oxide were made by reactive DC magnetron sputtering. Li⁺ intercalation/deintercalation showed that the electrochromic coloration efficiency depended on the Ce/W and Ce/Ti ratio, and at proper values of these ratios the films remained transparent irrespective of their ion content. Ti–Ce oxide combines this property with good electrochemical cycling durability, and this material can serve as a counter electrode in transparent electrochromic devices.     

The electrochromic properties of sputtered nickel oxide films

Electrochromic nickel oxide films were prepared by reactive RF sputtering from a nickel target in an oxygen atmosphere. The films were deposited as a compact 40 nm layer of trivalent nickel oxide, Ni₂O₃. Reduction and oxidation of the films in 1 M KOH resulted in bleaching and coloration, respectively. Voltammetry indicated that the eventual electrochromic reaction involved the β-Ni(OH)₂/β-NiOOH couple. In situ visible spectra showed electrochromic modulation of the transmittance throughout the visible range with a peak change in transmittance of about 60% at a wavelength of 500 nm. In situ spectra in the near-infrared region indicated improved electrochromic switching in this region; the sputtered nickel oxide film exhibited about a 30% change in transmittance in comparison to less than 10% for a similar electroprecipitated nickel hydroxide film. The sputtered nickel oxide films exhibited durable electrochromic switching for over 2500 coloration/bleaching cycles, a significant improvement over the less than 500 switching cycles exhibited by electroprecipitated nickel hydroxide films.     

Optical and electrochromic properties of oxygen sputtered tungsten oxide (WO3) thin films

Thin films of tungsten oxide (WO₃) were deposited onto glass, ITO coated glass and silicon substrates by pulsed DC magnetron sputtering (in active arc suppression mode) of tungsten metal with pure oxygen as sputter gas. The films were deposited at various oxygen pressures in the range 1.5×10⁻²−5.2×10⁻² mbar. The influence of oxygen sputters gas pressure on the structural, optical and electrochromic properties of the WO₃ thin films has been investigated. All the films grown at various oxygen pressures were found to be amorphous and near stoichiometric. A high refractive index of 2.1 (at λ=550 nm) was obtained for the film deposited at a sputtering pressure of 5.2×10⁻² mbar and it decreases at lower oxygen sputter pressure. The maximum optical band gap of 3.14 eV was obtained for the film deposited at 3.1×10⁻² mbar, and it decreases with increasing sputter pressure. The decrease in band gap and increase in refractive index for the films deposited at 5.2×10⁻² mbar is attributed to the densification of films due to ‘negative ion effects’ in sputter deposition of highly oxygenated targets. The electrochromic studies were performed by protonic intercalation/de-intercalation in the films using 0.5 M HCl dissolved in distilled water as electrolyte. The films deposited at high oxygen pressure are found to exhibit better electrochromic properties with high optical modulation (75%), high coloration efficiency (CE) (141.0 cm²/C) and less switching time at λ=550 nm; the enhanced electrochromism in these films is attributed to their low film density, smaller particle size and larger thickness. However, the faster color/bleach dynamics is these films is ascribed to the large insertion/removal of protons, as evident from the contact potential measurements (CPD) using Kelvin probe. The work function of the films deposited at 1.5 and 5.2×10⁻² mbar are 4.41 and 4.30 eV, respectively.     

Influence of sputtering conditions on the solar and luminous optical properties of amorphous LixWoy thin films

Thin films of amorphous tungsten oxide were deposited by sputtering onto glass substrates coated by conductive indium–tin oxide. The films were sputtered at different oxygen-to-argon flow ratios with different pressure and power. Elastic recoil detection analysis determined the density and the stoichiometry. X-ray diffraction measurements showed that the films were amorphous. The films were electrochemically intercalated with lithium ions. At several intercalation levels of each film, the optical reflectance and transmittance were measured in the wavelength range 0.3–2.5 μm. We study the effect of various sputtering conditions on the coloration efficiency of the films and on the luminous and solar optical properties. The O₂/Ar ratio and the sputter pressure determine to a large extent the optical absorption. As-deposited sputtered tungsten oxide with sufficiently little oxygen exhibits an absorption peak similar to the case of lithium intercalation.     

The electrochromic properties of nickel oxide thin films prepared by chemical vapor deposition

Electrochromic nickel oxide thin films were prepared in air by an atmospheric-pressure chemical vapor deposition method. The raw material was nickel acetylacetonate. Amorphous nickel oxide thin films were obtained at a substrate temperature 250°C. Reduction and oxidation of the films in 1 M KOH resulted in bleaching and coloration, respectively. Coulometry indicated that the coloration efficiency was 44 cm²/C.     

Properties of fluorine doped ZnO thin films deposited by magnetron sputtering

Fluorine doped ZnO (FZO) films were deposited on Corning glass by radio frequency (rf) magnetron sputtering of pure ZnO target in CF₄ containing gas mixtures, and the compositional, electrical, optical, and structural properties of the as-grown films as well as the vacuum-annealed films were investigated. The fluorine content in FZO films increased with increasing CF₄ content in sputter gas. FZO films deposited at elevated temperature of 150 °C had considerably lower fluorine content and showed a poorer electrical properties than the films deposited at room temperature. Despite high fluorine contents in the films, for all the FZO films, the carrier concentration remained below 2×10²⁰ cm⁻³, leading to fairly low doping efficiency level. Vacuum-annealing of the FZO films deposited at room temperature resulted in substantial increase of Hall mobilities, reaching as high as 43 cm²/Vs. This was attributed partly to the removing of oxygen vacancies and/or the forming chemical bonds with interstitial zinc atoms by fluorine interstitials and partly to the passivation effect of excess fluorine atoms by filling in the dangling bonds at the grain boundaries. For all the films with thickness of around 300 nm, the optical transmissions in visible were higher than 80%, and increased with increasing fluorine content up to 85% for the film with highest fluorine content.     

ZnO thin films deposited by RF magnetron sputtering: Effects of the annealing and atmosphere conditions on the photocatalytic hydrogen production

This work studied the effect of different annealing conditions of ZnO thin films grown by RF magnetron sputtering and their application as photocatalysts for hydrogen production without any sacrificial agent or co-catalyst. ZnO films were annealed in air, nitrogen, and argon atmospheres to study the effect of their physical properties in the photocatalytic activity. ZnO films showed high crystallinity and optical transparence of around 75–90% after annealing. Changes in composition and optical properties of the ZnO films were studied by x-ray photoelectron spectroscopy (XPS) and ellipsometry spectroscopy (SE), and results were correlated with the photocatalytic performance in hydrogen production. The highest photocatalytic hydrogen production was obtained with the ZnO thin film annealed in an air atmosphere with a result of 76 μmol.     

NiOxHy薄膜电致变色性能的研究

利用直流磁控溅射法，在Ｏ２＋Ｈ２的气氛下制备了ＮｉＯｘＨｙ薄膜，研究了不同氢气含量对薄膜的初始沉积态、漂白态和着色态透光性能的影响，含氢量为８０％时，薄膜的初始沉积态的平均可见光透射比最高。含氢量为６０％时，薄膜的电致变色能力最佳。用获得的ＮｉＯｘＨｙ薄膜制备的反射型全固态电致变色器件的控光范围可达７７％。对ＮｉＯｘＨｙ薄膜三种状态的红外吸收光谱分析表明，ＮｉＯｘＨｙ薄膜的变色机理可用：Ｎｉ（ＯＨ）２（漂白态）＝ＮｉＯＯＨ（着色态）＋Ｈ＋＋ｅ－表示。     

Low hydrogen containing amorphous carbon films—Growth and electrochemical properties as lithium battery anodes

Amorphous carbon films were deposited successfully on Cu foils by DC magnetron sputtering technique. Electrochemical performance of the film as lithium battery anode was evaluated across Li metal at 0.2 C rate in a non-aqueous electrolyte. The discharge curves showed unusually low irreversible capacity in the first cycle with a reversible capacity of ∼810 mAh g⁻¹, which is at least 2 times higher than that of graphitic carbon. For the first time we report here an amorphous carbon showing such a high reversibility in the first cycle, which is very much limited to the graphitic carbon. The deposited films were extensively characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profilometer for the structural and surface properties. The hydrogen content of the synthesized films was studied using residual gas analysis (RGA). The low hydrogen content and the low specific surface area of the synthesized amorphous carbon film are considered responsible for such a high first cycle columbic efficiency. The growth mechanism and the reasons for enhanced electrochemical performance of the carbon films are discussed.     

Electrochromic properties of NiOxHy thin films

NiO_xH_y films were prepared by DC magnetron sputtering in H₂/O₂ atmosphere. NiO_xH_y coatings with transparency and high electrochromic efficiency were obtained by changing H₂ content. A 60 nm thick NiO_xH_y film with transmittance of 0.57 (as-deposited state), 0.78 (bleached state) and 0.24 (coloured state) at wavelength of 550 nm was deposited in an atmosphere of H₂(60%)+O₂(40%). Analysis of infrared spectra (60002400 cm⁻¹) showed that the absorption peaks for bleached and colored states are associated with free ‘OH’ and OH stretching vibrations, respectively. XPS Ni2p core level spectra of colored NiO_xH_y film exhibited a peak at 856.2±0.2 eV which is attributed to Ni³⁺. Ni2p core level spectra of the bleached and as-deposited films exhibited two peaks at 856.4±0.2 and 854.6±0.2 eV which are attributed to Ni³⁺ and Ni²⁺.     

Influence of deposition temperature on electrochromic properties of sputtered W03 thin films

The influence of deposition temperature on the electrochromic properties of reactively sputtered WO₃ films has been investigated. A set of W0₃ films produced in the temperature range of 47–400°C is electrochemically cycled with a constant current supply, which provides an easy control of the charge injected into the films. Optical absorption after coloration, and, hence, the coloration efficiency of the films, significantly increases with increasing deposition temperature (up to 400°C) in the wavelength range of ∼ 1000–2500 nm. Both optical absorption and coloration efficiency decrease at the highest temperatures studied (350–400°C) over most of the visible spectrum (∼ 500–800 nm). Optical modulation across the solar spectrum remains fairly constant for charge injection of 10 mC/cm², and the modulation is quite satisfactory for all films for electrochromic device applications. The films produced at higher substrate temperatures show smaller modulation of the visible spectrum, compared with the films sputtered at lower substrate temperatures. This could be more suitable for some applications of the solar control systems. The resistance of the films during the electrochemical process is found to increase with increasing substrate temperature. This causes difficulty in charge injection, requiring significantly larger voltages in techniques such as a cyclic voltammetry for the films deposited at higher temperatures. As a result the good electrochromic performance of the films deposited at higher temperatures can be masked by experimental conditions.     

Exploration and optimization of ZrCo(Ti) type film for high hydrogen density and thermal stability of the hydride

Tritium target is of crucial importance in relation to the development of neutron generator apparatus. However, the prevalent Ti target is now suffering from the intricate procedures for activation, limited tritium content at room temperature (RT) and poor ability to fix the helium. Herein, a succession of new type ZrCo(Ti) alloy targets were designed and fabricated by magnetron sputtering. Firstly, the influence of technological parameters (types of substrate, sputtering temperatures, sputtering time and annealing temperatures) on the assemblage and also the hydrogen storage properties of the ZrCo films were systemically studied. The results show that high sputtering temperature is benefit to acquiring high crystallinity of ZrCo films, but the substrates seem to have no significant effect on that. The thickness and grain size of ZrCo film are both positively related to the sputtering time. However, the hydrogen uptake capacities (0.14 wt%~0.79 wt%) for all the prepared ZrCo films are relatively low. After that, the composition and microstructure of the ZrCo films were further regulated and optimized. On the one hand, Zr_1-xTi_xCo films were constructed by introduction of Ti element, achieving a higher hydrogen absorption capacity (~0.7 wt%), but with weak thermal stability in the subsequent hydrogen desorption process (~80% of hydrogen escaped at 500 °C). On the other hand, the surface of the ZrCo film was modified by a thin layer of Ti, forming a serious of double-layer ZrCo/Ti films. The ZrCo/Ti composite films not only achieve extremely high hydrogen storage capacity (1.85 wt%), but also maintain strong thermal stability (only 15.7% of hydrogen escaped at 500 °C). These findings related to the ZrCo(Ti) films in this paper provide crucial reference for the development of tritiated ZrCo film targets, and spark inspiration even for the design of other new-type tritiated film target.     

Improvements of water electrolysis in alkaline media at intermediate temperatures

Studies were carried out on the electrochemical splitting of hydrogen from water in an aqueous KOH solution at 110–140°C and in molten hydroxides at 300–400°C with the aim of increasing the energy efficiency of hydrogen production. The investigations on the electrolysis in an aqueous KOH solution were concentrated on developing metal oxide diaphragms and improved activated Ni electrodes. At 140°C and a pressure of 8 bar, a cell voltage of 1.55 V was obtained at a current density of 500 mA cm^?2. In molten NaOH at 350°C, a cell voltage of 1.3 V was achieved at a current density of 500 mA cm^?2. However, current yields were only ca 90%, due to side reactions producing peroxides. The formation of peroxides is significantly reduced in a LiOH/NaOH melt. Current yields of 100% have now been obtained at a cell voltage of 1.45 V and current density 500 mA cm^?2. The hydrogen and oxygen formed are separated by a Ni-diaphragm which is cathodically protected to eliminate corrosion.     

Highly efficient sputtered Ni-doped Cu2O photoelectrodes for solar hydrogen generation from water-splitting

Hydrogen gas can be converted to electricity through fuel cells and is considered as a friendly energy source. Herein, pure Cu₂O and Ni-doped Cu₂O thin films were deposited on glass substrates using the RF/DC-sputtering technique for hydrogen production via the photoelectrochemical (PEC) water-splitting process. The preferred orientation for pure and Ni-doped Cu₂O films was (111) crystallographic plane. The average nanograins size was decreased from 32.17 nm for pure to 10.40 nm through the doping process with Ni content. Field-emission scanning electron microscopy (FE-SEM) and ImageJ analysis showed that the pure Cu₂O and Ni-doped Cu₂O were composed of normal distribution of nanograins in a regular form. The optical bandgap of the Cu₂O film was decreased from 2.35 eV to 1.9 eV after doping with 2.6 wt% of Ni-dopants. The photoluminescence (PL) spectra for all the sputtered films were recorded at room temperature to examine the effect of Ni-dopants in the Cu₂O lattice. Pure and Ni-doped Cu₂O films were applied for PEC water splitting for hydrogen (H₂) production under white light and monochromatic illumination. The PEC studies displayed that increasing the Ni content up to 2.6 wt% in the pure Cu₂O films led to an increase in the photocurrent density to reach ?5.72 mA/cm². The optimum photoelectrode was studied for reproducibility, stability, and electrochemical impedance. The incident photon to current conversion efficiency (IPCE%) was 16.35% at 490 nm, and the applied bias photon to current conversion efficiency (ABPE%) was 0.90% at 0.65 V. Consequently, Ni-doped Cu₂O photoelectrodes are efficient and low-cost for practical and industrial solar H₂ production.     

Electrical and optical properties of ZnO thin film as a function of deposition parameters

Al-doped zinc oxide (AZO) and undoped zinc oxide (ZO) films have been prepared by rf magnetron sputtering. Films with low resistivities were achieved by using an Al-doped ZnO target and films with higher resistivities can be obtained by introducing oxygen during deposition. An AZO thin film which was fabricated with an rf power of 180 W, a sputtering pressure of 10 mTorr and thickness of 5000 Å showed the lowest resistivity of 1.4×10⁻⁴ Ω cm and transmittance of 95% in the visible range, and ZO film made by reactive sputtering with the above 10% oxygen content had the highest resistivity of 6×10¹⁴ Ω cm.     

Electrochromic properties of NiOx prepared by low vacuum evaporation

Nickel oxide (NiO_x) thin films were prepared by a low vacuum evaporation (LVE) onto fluorine doped tin oxide (FTO) coated glass substrates. Electrochromic test device (ECTD) was constructed by using these films as working electrodes, together with the FTO/glass as an opposite (counter) electrode in alkaline environment (0.1 M NaOH aqueous solution). Those films exhibited anodic electrochromism, changing color from transparent white-yellowish to dark brown. The coloration and bleaching times, defined as time to reach of the final change in transmittance, were found to be 1.7 and 4.2 s, respectively.The electrochromic characteristics were recorded by using cyclic voltammetry. The optical transmission spectra of the bleached and colored states were recorded in the visible part of the spectrum. The Fourier-transform infrared (FTIR) reflection spectra of the sample in the bleached and colored states were measured at near normal incidence angle. The dependence of the transmission of the sample at wavelength λ=670 nm on the electric charge transported to the anode were also examined. The coloration efficiency was calculated to be 32.4 cm²/C from the slope of the graphical presentation of the optical density as a function of the charge density, during the charge extraction. The spontaneous ex situ change of coloration with time and stability of the sample in the bleached and colored states were also examined.     

Synthesis and characterization of nanoporous ZnO and Pt/ZnO thin films for dye degradation and water splitting applications

In this paper, nanoporous ZnO and Pt/ZnO films were synthesized by a combination of simple spray pyrolysis and DC sputtering techniques at different flow rates and deposition times. X-ray diffraction, contact angle, and spectrophotometric measurements showed the growth of hexagonal ZnO Wurtzite phase with hydrophilic nature and high transparency in the visible region. By sputtering Pt nanoparticles on ZnO surfaces, the absorption edge is redshifted from UV region to the visible light region. The optical band gap of Pt/ZnO films is decreased from 3.74 to 1.86 eV as the deposition time increased to 4 min. The Pt/ZnO films exhibited higher photocatalytic activity and stability than pure ZnO films for methylene blue photodegradation. From the photoelectrochemical water splitting measurements, the current density of 4 min Pt/ZnO film is one hundred times greater than the value of pure ZnO film. The incident photon-to-current conversion efficiency at 470 nm was for the first time 76.2%.