WO3 Thin Films Research Articles

A WO3-NPs/MEMS NH3 Gas Sensor

This study exhibits WO3 nanoparticles (NPs) by using ultrasonic wave grinding and fabricates a WO3–NPs/MEMS gas sensor. The experimental results show that the WO3– NPs/MEMS gas sensor responds better to NH3 than to CO, CO2, and SO2. In terms of the stability and the reproducibility of the WO3–NPs/MEMS gas sensor, the average sensing response is about 16% and there is an inaccuracy of <±0.5% when the sensor is operated at 142 °C with 1.3 ppm NH3 gas. The WO3–NPs sensor has a better sensing response to NH3 than the WO3-thin film and original-WO3 powder sensors. This study shows that WO3 nanoparticles have a good sensing response to NH3 gas.

Influence of magnetron sputtering process on the stability of WO3 thin film gas sensor

Influence of magnetron sputtering process on the stability of WO3 thin film gas sensor

Enhanced electrochromic properties of Ag-incorporated WO3 nanocomposite thin films

WO3 nanocomposite thin films, in which metal nanoparticles are incorporated into a WO3 matrix, offer an enhanced electrochromic response speed with color neutrality. This article reports the structural, optical, and electrochemical properties of Ag nanoparticle-incorporated electrochromic WO3 thin films with different concentrations. Room-temperature-sputtered thin films using composite targets with a low Ag concentration exhibited a random distribution of small nanoparticles. In contrast, in the film with a higher Ag concentration, the particles were merged, resulting in a single or polycrystalline phase. Surface plasmon resonance peaks were observed in the absorption spectra of the Ag–WO3 composite films, indicating the formation of metallic nanoparticles, which was also confirmed via high-resolution transmission electron microscopy. The optical bandgaps decreased gradually from 3.15 eV for WO3-δ to 3.02 and 2.99 eV for W0.97Ag0.03O3-δ and W0.91Ag0.09O3-δ thin films, respectively. The W0.91Ag0.09O3-δ thin film showed a faster switching time of 2.6 s for coloring and 4.8 s for bleaching with a higher coloration efficiency of 66.52 cm2/C than those of the WO3-δ thin film, which were 3.8 s, 6.8 s, and 58.68 cm2/C, respectively. However, transmittance modulation in the W0.91Ag0.09O3-δ thin film was inferior to that in the other films. Furthermore, the W0.91Ag0.09O3-δ thin films were black in the colored state, whereas the bare WO3-δ and W0.97Ag0.03O3-δ thin films were Prussian blue, suggesting the realization of color neutrality through the incorporation of Ag nanoparticles.

Structural and electrochemical studies of WO3 coated TiO2 nanorod hybrid thin films for electrochromic applications

This work presents the fabrication of Titanium dioxide (TiO2) nanorods/Tungsten oxide (WO3) hybrid thin films and the influence of nanostructures on the electrochromic behavior of the films. WO3 thin films were deposited at a constant substrate temperature of 673 K under various partial pressures of oxygen (ppO2). Also, Tungsten nanorods were grown on Fluorine doped tin oxide (FTO) coated glass substrate by hydrothermal process. Optimized WO3 films were coated on the TiO2 nanorod film by a sputter deposition method. Material, optical, electrical, and electrochemical analysis have been performed on the films using XRD, Raman, XPS, UV-Visible spectrometer and Cyclic voltammetry. The enhanced coloration efficiency (η) of the optimized WO3 films is found to be attributed to its large active surface area which favored H+ ions intercalation in the films. Also, the TiO2 nanorods/WO3 hybrid films exhibited a good electrochemical property in terms of the diffusion coefficient of 1.8 × 10−7 cm2/s better than those of pure WO3 and TiO2 nanorods.

A sight of view on electrical impacts, structural properties and surface roughness of tungsten trioxide thin film: effect of substrate temperatures in WO3/Si device fabrication

Monoclinic WO3 thin films have been effectively deposited by a simple spray pyrolysis technique at a molar concentration of 0.01 M on a glass substrate in the temperature range of 473 to 673 K. These WO3 films were used as an interlayer between the metal and the semiconductor, which formed the basic structure of the photodetector. Effect of substrate temperature on WO3 films during the process of the deposition was systematically interpreted with respect to the structural, morphological, optical and electrical properties of the WO3 films. The x-ray diffraction pattern revealed the polycrystalline nature of the prepared films with monoclinic phases. At the substrate temperature of 623 K, the nano-thin films were strongly bonded to each other as observed from the FE-SEM images. Visible and ultraviolet spectroscopies indicated the band gap (Eg) of the WO3 thin film is 3.30 eV. The dc electrical study recorded a sharp increase in the electrical conductivity of the prepared film at substrate temperature of 623 K for tungsten trioxide. It is worth noting that all diodes showed a positive photoresponse under illumination. In particular, the photodetector with the thickness of 300 nm showed higher responsivity 0.02 A/W and detection specificity 8.29 × 1010 Jones.

The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography.

Tungsten trioxide (WO3) is a versatile n-type semiconductor with outstanding chromogenic properties highly used to fabricate sensors and electrochromic devices. We present a comprehensive experimental study related to piezoresponse with piezoelectric coefficient d33 = 35 pmV-1 on WO3 thin films ~200 nm deposited using RF-sputtering onto alumina (Al2O3) substrate with post-deposit annealing treatment of 400 °C in a 3% H2/N2-forming gas environment. X-ray diffraction (XRD) confirms a mixture of orthorhombic and tetragonal phases of WO3 with domains with different polarization orientations and hysteresis behavior as observed by piezoresponse force microscopy (PFM). Furthermore, using atom probe tomography (APT), the microstructure reveals the formation of N2-filled nanovoids that acts as strain centers producing a local deformation of the WO3 lattice into a non-centrosymmetric structure, which is related to piezoresponse observations.

Computational modeling and analysis of a chemical gas sensor utilizing WO3 thin films for NO2 detection

Computational modeling and analysis of a chemical gas sensor utilizing WO3 thin films for NO2 detection

The effect of gold Nanoparticles on Structural and Electrical properties of WO3 thin films

Chemical spray pyrolysis technique was used at temperature 250˚C with annealing temperature at 400C˚( for 1hour) to deposition tungsten oxide thin film with different doping concentration of Au nanoparticle (0, 10, 20, 30 and 40) wt.% on glass substrate with thickness about 100 nm. The structural and electrical properties were investigated. The structure properties shows that the films at substrate by x-ray diffraction (XRD) temperature (250˚C) was amorphous structure while at annealing temperature have a polycrystalline structure with the preferred orientation of (200) , all the samples have a hexagonal structure for WO3 and Au gold nanoparticles have a cubic structure .The mechanisms of dc-conductivity of un-doped WO3 and doped with Au (10,20,30 and 40) wt.% thin films at the range (303 to 473) K have been discussed , there is decrease in conductivity with the increase in the doping concentration and hall measurements show that all films have a negative hall coefficient and nH increases with the increase of Au dopant ratio and decreasing in carrier mobility (μH) with increasing of Au .

Synergistic effects of Pd decoration and substrates on the NO2 sensing performance of sprayed WO3 thin films

The selective detection of NO2 is achieved using Pd decorated WO3 thin films deposited on glass (WO3G) and alumina (WO3A) substrates. WO3A film shows superior performance over WO3G film in terms of sensitivity, response magnitude and response and recovery time. Lower detection limit of 2 ppm is achieved using WO3A film for which gas response was 20 % whereas for WO3G film response was 9 %. In particular, higher gas response towards NO2 is observed for WO3A film, which is attributed to the high surface roughness and high catalytic activity of Pd causing enhanced spillover and effective diffusion of NO2.

Binder-free room-temperature synthesis of amorphous-WO3 thin film on FTO, ITO, and stainless steel by electrodeposition for electrochromic application

For electrochromic applications, binders are frequently employed to appropriately affix thin films to transparent conductive substrates like fluorine and indium-doped tin oxide glass plates (FTO and ITO) and stainless steel (SS). The different WO3 nanostructure materials are specifically formed using a variety of chemical and physical processes, but WO3 thin films are not sticky on the substrates without etching. Hence in the present research article, the nanostructured WO3 thin films were effectively deposited using straightforward, affordable anodic electrodeposition procedures on a variety of substrates, including ITO, FTO, and SS, without etching. The XRD analysis confirmed that the nanostructured WO3 materials exhibit amorphous nature (a-WO3). The uniformly deposited a-WO3 film shows the cracked morphological structures. The deposited a-WO3 film was confirmed by FTIR analysis. The nanostructured a-WO3 exhibits excellent electrochromic properties with the highest coloration efficiency (CE) on the FTO 191.4 cm2C-1 at 633 nm wavelength. The fastest electrochromic coloration (1.22 s) and bleaching (1.29 s) response time of nanostructured a-WO3 are observed on FTO substrates, respectively. The cycling stability of electrochromic a-WO3 was shown to be good up to 3000 cycles on FTO substrate.

Regulating the growth of WO3 thin films using ammonium acetate as structure directing agent

The optimization of morphology and structure of tungsten trioxide (WO3) needs to be performed to target some specific applications. In fields such as electrochromics and sensing, the study of electrochemical reaction kinetics is important as it defines the rate of reaction occurring on the WO3 surface. In the present study, WO3 thin films are grown on fluorine-doped tin oxide (FTO) glass by in-situ hydrothermal technique. To regulate the growth of the WO3 layer employing the hydrothermal method, ammonium acetate has been used as a capping agent (CA) and its molar ratio for tungsten, i.e., CA/W, was varied from 0 to 6. Cyclic voltammetry (CV) revealed that the thin film prepared with CA/W of 4 has improved Li+ ions intercalation/deintercalation which leads to fast reaction kinetics. Better electrochemical reaction kinetics in WO3 thin film with a CA/W ratio of 4 compared with the samples having CA/W of 0 and 2 is ascribed to its improved morphology and phase. X-ray diffraction and scanning electron microscopy analysis showed negligible thin film growth with a CA/W ratio of 6. Overall, WO3 thin film with a CA/W ratio of 4 showed excellent performance, making it a good candidate for electrochromics or other related applications.

Visible-light-induced superhydrophilicity of crystallized WO3 thin films fabricated by using a newly isolated W6+ complex salt of citric acid.

Transparent tungsten trioxide thin films, which demonstrated visible-light (Vis-light)-induced superhydrophilicity, with thicknesses of 100-120 nm, adhesion strengths greater than 49 MPa, bandgap energies of 2.8-2.9 eV, and haze values of 0.4-0.5%, were fabricated using a solution-based process on quartz glass substrates. The precursor solution was prepared by dissolving a W6+ complex salt isolated from a reacted solution of tungstic acid, citric acid, and dibutylamine in H2O, in ethanol. By heating the spin-coated films in air for 30 min at temperatures higher than 500 °C, crystallized WO3 thin films were obtained. The O/W atomic ratio was evaluated to be 2.90, based on the peak area analysis of X-ray photoelectron spectroscopy spectra of the thin-film surfaces, indicating the co-presence of W5+ ions. The water contact angle on film surfaces, which was approximately 25° prior to light irradiation, decreased to less than 10° upon irradiation with 0.06 mW cm-2 Vis-light for only 20 min at 20-25 °C and a relative humidity (RH) of 40-50%. By comparing the contact angle changes at RH values of 20-25%, it was revealed that the interaction between ambient water molecules and the partially O-deficient WO3 thin films plays an important role in achieving photoinduced superhydrophilicity.

Tungsten oxide thin film for room temperature nitrogen dioxide gas sensing

Tungsten oxide (WO3) thin films for gas sensing have been successfully deposited using reactive direct current (DC) magnetron sputtering at different deposition temperatures (300 °C, 400 °C and 500 °C). The structural, morphological properties, thickness and composition have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rutherford backscattering spectrometry (RBS) techniques. To investigate the effect of deposition temperature on the gas sensing properties of deposited thin films on alumina substrates, was conducted using the Kenosistec gas sensing unit. WO3 thin film deposited at 500 °C exhibited a higher response when sensing Nitrogen dioxide (NO2) at room temperature as compared to the thin films prepared at 300 °C and 400 °C, respectively. However, as deposited WO3 thin films exhibited low sensitivity when sensing reducing gases such as hydrogen (H2) and ammonia (NH3), which was an indication of good selectivity properties of WO3 related sensors.

Giant saturation absorption of tungsten trioxide film prepared based on the seedless layer hydrothermal method

Nonlinear materials have gained wide interest as saturable absorbers and pulse compression for pulsed laser applications due to their unique optical properties. This work investigates the third-order nonlinear phenomenon of tungsten trioxide (WO3) thin films. The giant nonlinear absorption and nonlinear refractive index of WO3 thin films were characterized by Z-scan method at 800 nm. We experimentally observed the giant saturable absorption (SA) and nonlinear refractive index of WO3 thin films prepared by the seedless layer hydrothermal method, with SA coefficient being as high as –2.59 × 105 cm⋅GW−1. The SA coefficient is at least one order of magnitude larger than those of the conventional semiconductors. The nonlinear refractive index n 2 of WO3 film has been observed for the first time in recent studies and the corresponding coefficient can be up to 1.793 cm2⋅GW−1. The large third-order nonlinear optical (NLO) response enables WO3 thin films to be promising candidates for optoelectronic and photonic applications in the near-infrared domain.

Tailoring the Emission Behavior of WO3 Thin Films by Eu3+ Ions for Light-Emitting Applications

The article reports the successful fabrication of Eu3+-doped WO3 thin films via the radio-frequency magnetron sputtering (RFMS) technique. To our knowledge, this is the first study showing the tunable visible emission (blue to bluish red) from a WO3:Eu3+ thin film system using RFMS. X-ray diffractograms revealed that the crystalline nature of these thin films increased upto 3 wt% of the Eu3+ concentration. The diffraction peaks in the crystalline films are matched well with the monoclinic crystalline phase of WO3, but for all the films', micro-Raman spectra detected bands related to WO3 monoclinic phase. Vibrational and surface studies reveal the amorphous/semi-crystalline behavior of the 10 wt% Eu3+-doped sample. Valence state determination shows the trivalent state of Eu ions in doped films. In the 400-900 nm regions, the fabricated thin films show an average optical transparency of ~51-85%. Moreover, the band gap energy gradually reduces from 2.95 to 2.49 eV, with an enhancement of the Eu3+-doping content. The doped films, except the one at a higher doping concentration (10 wt%), show unique emissions of Eu3+ ions, besides the band edge emission of WO3. With an enhancement of the Eu3+ content, the concentration quenching process of the Eu3+ ions' emission intensities is visible. The variation in CIE chromaticity coordinates suggest that the overall emission color can be altered from blue to bluish red by changing the Eu3+ ion concentration.

Facile Synthesis of Pure and Cr-Doped WO3 Thin Films for the Detection of Xylene at Room Temperature.

This paper focused on the preparation of pure and Cr-doped tungsten trioxide (WO3) thin films using the spray pyrolysis method. Different techniques were adopted to analyze these films' structural and morphological properties. The X-ray detection analysis showed that the average crystallite size of the WO3-nanostructured thin films increased as the Cr doping concentration increased. The atomic force microscopy results showed that the root-mean-square roughness of the films increased with Cr doping concentration up to 3 wt % and then decreased. The increased roughness is favorable for gas-sensing applications. Surface morphology and elemental analysis of the films were studied by field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy measurements. The 3 wt % Cr-WO3 has a large nanoflake-like structure with high surface roughness and porous morphology. Gas-sensing characteristics of undoped and Cr-doped WO3 thin films were investigated with various gases at room temperature. The results showed that 3 wt % Cr-doped WO3 film performed the maximum response toward 50 ppm of xylene with excellent selectivity at room temperature. We believe that increased lattice defects, surface morphology, and roughness due to Cr doping in the WO3 crystal matrix might be responsible for increased xylene sensitivity.

Facile preparation of electrodes based on WO3 nanostructures modified with C and S used as anode materials for Li‐ion batteries

AbstractAn appropriate morphological and structure matrix configuration where lithium ions could insert and de‐insert is essential for lithium‐ion batteries (LiB). Tungsten oxides (WO3) are especially attractive materials for this aim. In this research, the effects of the morphology and composition of WO3 nanostructures on the charge/discharge behavior for Li‐ion batteries are methodically examined. On the one hand, nanostructured WO3 thin film was effectively synthesized by an electrochemical procedure. Then, an annealing treatment at 600°C in air environment for 4 h was carried out. In the second electrode synthesized, a carbon layer was uniformly deposited on WO3 nanostructures to obtain a WO3/C electrode. Finally, WO3/WS2 electrodes were prepared by means of in situ sulfurization of WO3 one‐step solid‐state synthesis using tungsten trioxide (WO3) and thiourea as precursor material. By using X‐ray photoelectron spectroscopy, X‐ray diffraction analysis, transmission electron microscopy, Raman spectra, and field‐emission scanning electron microscopy, the three electrodes have been morphologically characterized. Electrochemical properties were analyzed by cyclic voltammogram, galvanostatic charge/discharge cycling, and electrochemical impedance spectroscopy. Among all the synthesized samples, WO3/C nanostructures reveal the best performance as they exhibit the greatest discharge capacity and cycle performance (820 mA h g−1).

Structure and electrochromic properties of WO3 thin films by direct current, pulsed direct current, and radio frequency magnetron sputtering from metallic and ceramic targets

The structure, morphology, and electrochromic properties of sputtered-WO3 thin films from ceramic and metallic targets were investigated. The films were produced using different types of power sources, namely, direct current (DC), pulsed DC, and radio frequency (RF) generators. Highly transparent as-deposited WO3 thin films grown at room temperature using each target changed to dark blue upon introduction of an electric field in electrolyte regardless of types of sputtering power. WO3 films obtained by sputtering the ceramic target using a pulsed DC power exhibited a large transmittance difference of 97.5% and high coloration efficiency of 55.2 cm2/C compared to the films using DC and RF powers, these films had higher response speeds and stable transmittance modulation after long-term cycle tests. WO3 thin films produced by sputtering a metallic tungsten target showed enhanced electrochromic performance when grown under DC power and a coloration efficiency of 69.1 cm2/C due to their porous microstructure. This article presents methods for the fabrication of low-cost and large-scale oxide electronic devices for various applications, such as electrochromic displays, that can be applied for mass production.

Effect of tungsten oxide thin films deposited on cerium oxide nano rods for electrochromic applications

Cerium oxide Nanorods were synthesized on Fluorine-doped Tin Oxide (FTO) coated glass substrate by hydrothermal process. Optimized Tungsten Oxide (WO3) films were coated on the top of cerium oxide (CeO2) Nanorods by a sputter deposition method. WO3 thin film was deposited at a constant substrate temperature of 300K under partial pressures of oxygen (ppo2) at 8 × 10−4 mbar. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), UV–Visible spectrometer, and cyclic voltammetry were used to analyse the films for material, optical, surface, and electrochemical properties. The improved CeO2/WO3 films increased the cathodic peak current which is related to their high active surface area and increased H+ ions intercalation in the films. In addition, the CeO2 Nanorods/WO3 hybrid films had a better electrochemical property in terms of the diffusion coefficient of 5.53 × 10−8 cm2/s. These structures produce considerable coloration efficiency when compared to pure WO3 (9.88, 10.19 and, 8.14 cm2/C at 700 nm). This study predicts that how varying concentrations of cerium oxide Nano rods change WO3 electrochemical behaviour which will help to choose the right rare earth elements and concentrations for energy-efficient smart windows.

Correlation between Thickness and Optical Properties in Nanocrystalline γ-Monoclinic WO3 Thin Films

Results from the analysis of the variation of structural defects, such as oxygen vacancies indicate that by adjusting the thickness of the WO3 films, fabricated by DC reactive sputtering, it is possible to modulate the oxygen vacancies concentration. This has a tremendous influence on the applications of these semiconductor materials. The thicknesses analyzed here are 42, 66, and 131 nm. After the annealing process at 500 °C, films were directly transformed to a stable γ-monoclinic crystal structure with P21/n space group, with a preferential orientation in the (200) plane. Atomic force microscopy exhibits nanometer range particle size with the highest roughness and higher surface area for the thinner film. FTIR analysis shows the presence of characteristic bands of the double bond stretching vibrational modes (W=O) and stretching vibrations of the γ(W-O-W) bonds corresponding to the monoclinic WO3. Raman bands located at 345, and 435 cm−1 are ascribed to the presence of W5+ species that induces the formation of oxygen vacancies VO. The thinner film shows a decrease in the optical indirect band gap attributed to the formation of oxygen vacancies in combination with W5+ species that induce the formation of energy states within the forbidden band gap range.