Tungsten Trioxide Films Research Articles

Opto-electronic responses of large area WSe2 layers synthesized by chemical conversion of WO3 thin films

Atomically thin tungsten diselenide (WSe2) has drawn much interest due to its remarkable optical properties and potential applications in next-generation optoelectronics and energy harvesting devices. High-quality, wafer-scale synthesis of such two-dimensional (2D) semiconductors is necessary for their practical applications. Chemical vapor deposition (CVD) is a promising method for synthesizing large-area thin films of 2D materials where the constituent elements are of widely different vapor pressure. Herein, we demonstrate large-area synthesis of the 2H phase of WSe2 with a precise control over the 2D film thickness. The first step of this process is the deposition of tungsten trioxide (WO3) films of a well-defined thickness by thermal evaporation over large areas. The subsequent selenization of these films in an atmospheric pressure CVD reactor, yields high-quality uniform films of WSe2. The quality of these films is ascertained by measuring their characteristic Raman active vibrational modes and layer thickness dependent optical absorption and photoluminescence. The photoconductivity (PC) of these films has been measured with 405, 532 and 915 nm laser excitation. We note an increase in the PC of the films with their thickness. The best photoresponsivity and detectivity obtained are 11.3 mA/W and 1.42 × 108 Jones respectively. These results are promising to create photo-transistor arrays over large areas using such WO3 processed films.

Structural and electrochromic property control of WO3 films through fine-tuning of film-forming parameters

Abstract Tungsten trioxide (WO3) films, extensively investigated for their remarkable electrochromic properties, have proven to be highly versatile in numerous applications. However, the challenge of achieving large-scale WO3 films with substantial dimensions and volumes remains a critical obstacle for industrial-scale production. Among the available techniques, magnetron sputtering stands out as the most efficient and straightforward method for the industrial preparation of WO3 films. In this comprehensive study, we meticulously explored the impact of various process parameters in magnetron sputtering on the film formation properties. By employing a controlled variable approach, we systematically investigated the influence of gas flow (Ar), sputtering pressure, power, and time. Our meticulous observations revealed that each parameter exerted distinct effects on the intricate film formation process. Careful analysis of the final dataset unequivocally demonstrated that when the sputtering conditions were meticulously optimized, the resulting films exhibited an extraordinary maximum transmittance change of 85% at a specific wavelength of 0.6 μm. Furthermore, these films showcased rapid coloring and bleaching response times, clocking in at an impressive 15 and 20 s, respectively, without any significant degradation even after undergoing 5,000 cycles. These groundbreaking findings provide invaluable insights into the intricate film formation process associated with magnetron-sputtered WO3.

Ion Transfer Kinetics at the Tungsten Oxide Interface

Investigating the kinetics of interfacial ion transfer is imperative for the enhancement of electrochemical energy storage technologies, such as cation batteries. Consequently, we study the enigmatic proton transfer mechanisms that occur at solid-liquid interfaces to evaluate parameters that may modulate the optimization of battery efficiency. Utilizing electrochemical techniques, our objective is to deconvolute the mechanistic and rate-limiting factors associated with proton insertion from an acidic aqueous electrolyte into a thin film of tungsten trioxide (WO3). While WO3 has been investigated as a battery anode, the kinetics of cation insertion remain inadequately explored despite their effects on system efficiency. Through the Potentiostatic Intermittent Titration Technique (PITT), a developed application of chronoamperometry, along with Butler-Volmer equation fitting, our research endeavors to define the exchange current density and activation energy pertinent to cation insertion. The broader implications of exploring interfacial ion transfer phenomena manifest in advancing the fundamental understanding of energy storage processes.

Relationship between crystal orientation and energy storage capacity in WO3 photoelectrodes for water splitting

For photoelectrochemical water splitting, tungsten trioxide (WO3) films with a monoclinic structure were synthesized on fluorine-doped tin oxide coated glass substrates with a vacuum evaporation method. To control the WO3 film thickness from 0.42 to 5.6 μm, the crystal orientation was intergraded from the (200) crystal plane to the (002) one. In x-ray diffraction measurements, the intensity ratio of the (002) crystal plane to the (200) one was defined as rp. In the WO3 photoelectrode with higher (002)-preferred orientation, the photocurrent continued to flow even when the incident light against the photoelectrode was completely blocked after the irradiation for 60 s. This suggests that hydrogen continues to be produced owing to the electrons charged by the formation of a hydrogen tungsten bronze (HxWO3) phase. After 72 s, the photocurrent density of the WO3 photoelectrode with rp = 42 became one-tenth of the value before the incident light was blocked. This charge release time was remarkably long compared to those of the WO3 photoelectrodes with (200)-preferred orientation and non-orientation. Therefore, it was considered that the hydrogen ion diffusion through the defects in the WO3 crystals tends to occur in the [002] crystal direction. However, the improvement in the (002)-preferred orientation can facilitate the structural change from the WO3 phase to the HxWO3 one for the entire film.

Solid–liquid heterojunction UV photoelectrochemical photodetector based on WO3 nanosheets and acidic electrolyte

The acid-resistant tungsten trioxide photoelectrochemical solid–liquid ultraviolet (UV) photodetector uses a thin film of tungsten trioxide as the photoelectrode, forming a stable heterojunction with the electrolyte. This study employed band theory and double electron layer theory to analyze the mechanisms underlying the effect of pH on the redox potential and photocurrent, utilizing the ion product constant of water and the Nernst equation. By applying the principles of energy band theory and the two-electron layer model, the electron transfer process was analyzed and explained. These findings hold significant promise for enhancing solid–liquid heterojunction UV photodetectors. Tungsten trioxide has fast response and high sensitivity under extreme conditions. The device performance of WO3 nanosheets fabricated by annealing at 300 °C for one hour is excellent, including a rise time of 0.7 s, decay time of 6.8 s, photosensitivity of 1.90, and photoresponsivity of 2.31 mA/W. 0.5M sulfuric acid produced the highest photocurrent (5.46 μA) and sensitivity (14.07). This material has potential applications in optoelectronics, catalysis, sensing, water treatment, and air purification.

Fabrication and application of two-dimensional tungsten disulfide thin film

To form a tungsten disulfide film, a tungsten trioxide film is deposited first and then hydrogen sulfide is injected into the furnace tube to sulfide the tungsten trioxide film in a high-temperature environment. Due to the need to accurately control the thickness of tungsten trioxide, the power of the RF sputtering machine was reduced as much as possible in a stable condition in the experiment and the bias voltage during each process was monitored. In this experiment, a sapphire substrate and a silicon substrate with 200[Formula: see text]nm silicon dioxide are used. Then use optical instruments such as Raman optics, ellipsometers and high-resolution electron transmission microscopes, atomic force microscopes and other instruments for further measurement. The analysis results show that we have successfully made tungsten disulfide films of different thicknesses. Moreover, two-dimensional tungsten disulfide thin film has a response to light, gas and pH and related devices have been successfully fabricated in experiments. Among them, comparing the single-layer film and the double-layer film, the film quality of the double-layer film is better. The quality of the film grown on the sapphire substrate is also better than the quality of the film grown on the silicon dioxide substrate.

Preparation of WO3-based flexible electrochromic fabrics and their near infrared shielding application

In this work, tungsten trioxide (WO3) films are prepared on carbon cloth using a one-step hydrothermal method.

Effect of ratio gold nanoparticles on the properties and efficiency photovoltaic of thin films of amorphous tungsten trioxide

At a substrate temperature of 320 o C, a chemical spray pyrolysis approach was applied. to create tungsten oxide thin films on glass substrates with varying Au nanoparticle doping concentrations (0, 0.04 and 0.08 M) that have a thickness of roughly 250 nm. Investigated were the structural and optical characteristics. The films were amorphous to the pure films at the substrate temperature (320 °C), according to X-ray diffraction and remain so even after adding GNPs, because the WO3 structure is amorphous in all samples, whereas the cubic structure of the gold nanoparticles. The morphology of the films was examined using atomic force microscopy (AFM), which showed a decrease in the grain size of the films doped with gold compared to the thin films before the doping process. a UV-Vis spectrophotometer was used to examine the membranes' optical characteristics between the wavelengths of (300-1000) nm. was the optical energy gap of the films (3.23) eV for tungsten oxide film and decreased after adding nanoscale gold to (3.04, 2.95) eV for films doped with different proportions of Au NPs (0.04, 0.08 M), respectively. Hall testing confirms that with 8 (mM) Gold (Au) doping, WO3 material of the n type was obtained with a maximum carrier mobility of 219.92(cm2 /Vs) and conductivity of 6.52 (Ω.cm)-1 . The I-V characteristics of the photovoltaic formed under illumination were determined by measuring the incident power density (100 mW/cm2 ) at varied Au doping levels.

Long-life Inorganic Electrochromic Device Based on WO3 and PB Films with Fast Switching Respond

Complementary electrochromic devices were fabricated by using tungsten trioxide (WO3) film as working electrode, Prussian blue (PB) film as counter electrode and 0.1 M lithium perchlorate in propylene carbonate as electrolyte. The XRD result presents that WO3 and PB films are amorphous, which is favourable for a fast ion intercalation-deintercalation process. The device was tested under potentiostatic control using ±1.3 V steps, and changed its color between blue and colorless. It has a fast-switching respond (about 1.5 s for colouring and 2 s for bleaching) and could withstand 100,000 cycles with little change in its optical contrast.

Amorphous bismuth-doped WO3 film: Fast-switching time and high-performance proton-based aqueous electrochromic device

Tungsten trioxide (WO3) film, recognized as one of the most promising electrochromic materials due to its exceptional electrochemical characteristics, is extensively utilized in fabricating electrochromic devices. The use of bismuth-doped WO3 (Bi-WO3) films in photoelectrocatalysis has been extensively studied. However, its potential in electrochromism remains unexplored. Herein, amorphous Bi-WO3 films with enhanced electrochromic performance are synthesized through a simple sol–gel method. The effects of Bi doping amount and sol concentration on the electrochromic properties of Bi-WO3 films are investigated. The optimized Bi-WO3 film displays excellent electrochromic performance, encompassing high optical contrast (ΔT = 81% at 630 nm), fast switching time (2.4/1.2 s for coloring and bleaching), and high coloration efficiency (55.84 cm2C−1). An electrochromic device is assembled utilizing an amorphous Bi-WO3 film as the electrochromic layer with Cu foil as the counter electrode. The fascinating electrochromic properties of amorphous Bi-WO3 thin films and the high activity features of proton enable the assembled ECD to have a suitable working voltage range (1.1 V) in aqueous electrolytes. Besides, the electrochromic device demonstrates outstanding properties (ΔT = 70%, tc = 3 s, tb = 0.9 s) and provides a helpful strategy for the facile processing of high-performance electrochromic devices.

WO3 work function enhancement induced by filamentous films deposited by resistive heating evaporation technique

Tungsten trioxide (WO3) films are of great interest due to their electronic properties which can be tuned by surface nanostructuring leading to enhanced efficiency for gas sensing, energy storage or electrochromic applications. Resistive heating of tungsten (W) filaments at pressures of few Pa in an oxygen O2 atmosphere has already demonstrated its capability to form porous, micro/nano-structured, cheap and fast films making it suitable for industrial applications. This work presents stoichiometric WO3 films produced by applying a current into a W filament for pressures in the range of 2–20 Pa. The increase of the pressure above 7.5 Pa led to amorphous WO3 films with a newly filamentous morphology. As a function of the pressure, the work function (WF) of the films was determined in-vacuo by aims of Ultraviolet Photoelectron Spectroscopy (UPS). In addition to the high surface to volume ratio of the films, the WF exhibited an increase from 5.8 eV, for a conventional WO3 film, to a maximum of 8.7 eV at 20 Pa. This change corresponds to an increase of the WF of about 50% compared to 5.8 eV making our films suitable for a large variety of applications. The highering of the WF is mainly induced by the change of morphology to filamentous structures, the defect induced by the amorphous structure and the nanometric size of the filaments leading to the confinement of the electrons in the valence band for our WO3 films. Additionally, a change from p to n-type polarity is reported in-vacuo when increasing the pressure from 7.5 to 20 Pa with the formation of an intermediate band at around 0.8 eV below the Fermi level. Additionally, molybdenum trioxide (MoO3) and vanadium pentoxide (V2O5) filamentous films were deposited via the resistive evaporation technique in an O2 atmosphere. Similarly, copper, aluminium and molybdenum wires were used, leading to the formation of islands having foam-like structures analogous to the WO3.

Time-dependent lateral diffusion in WO[formula omitted] thin films

We have studied the anomalous lateral diffusion process in thin tungsten trioxide films by optical means. The diffusion process seems to start at imperfections within the film a few seconds after the H+ ion intercalation begins, and progresses parallel to the surface of the film. We measured the mean square displacement of the diffusion front and used its time-dependence to calculate the instantaneous diffusion coefficient. The anomalous exponents are found to be 2.24 and 2.92 for 400 nm and 270 nm thick films, respectively. We explain the observed large diffusion coefficients and depth dependence of the expansion of the film by interfacial job-sharing diffusion of electrons and protons. Raman measurements were also carried out on virgin films, and on films after the lateral diffusion. Although the observed spectrum after the lateral diffusion is, in general, consistent with the literature for H+ intercalated films, we observe an additional strong band at 855 cm−1. This lateral diffusion process is observed to be irreversible; therefore, it has to be avoided in electrochromic switching devices based on WO3.

Correlation between the Experimental and Theoretical Photoelectrochemical Response of a WO3 Electrode for Efficient Water Splitting through the Implementation of an Artificial Neural Network

Since the discovery of photoelectrochemical (PEC) water splitting with titanium dioxide electrodes in the presence of ultraviolet light, much work has been conducted to build an effective PEC water splitting system and develop novel photoelectrodes. Using a facile and controllable electrodeposition method, a thin tungsten trioxide (WO3) film electrode onto a stainless steel (SS) substrate was synthetized. The effect of the deposition time on the structural, morphological, optical, and electrical properties of the as-grown WO3 thin films was assessed. XRD spectra of the obtained films reveal the polycrystalline nature of WO3 with a triclinic phase and exhibit a sharp transition to the (002) plane when the deposition time was extended beyond 10 min. The surface morphology showed a remarkable change in the grain size, thickness, and surface roughness when varying the deposition time. UV–Vis spectrophotometry revealed that the optical band gap values of WO3 decreased from 1.78 to 1.36 eV by extending the electrodeposition duration from 10 to 30 min, respectively. Notably, as indicated from the PEC measurements, the obtained photoelectrode exhibited the effects of the deposition time on the photocurrent density, and the maximum value obtained was around 0.07 mA cm−2 for the sample deposited at 10 min. Finally, this study presents for the first time an artificial neural network model to predict the PEC behavior of the prepared photoanode, with a highly satisfactory performance of less than 0.05% error. The low cost and simply synthetized WO3/SS electrode with superior electrochemical performance and the excellent correlation between the experimental and theoretical results demonstrate its potential for practical application in water splitting and hydrogen production.

Long-term stability electrochromic electrodes based on porous tungsten trioxide and nickel oxide films via a facile triple pulse electrodeposition

Herein, a facile triple pulse electrodeposition was used to fabricate porous films such as tungsten trioxide (WO3) and nickel oxide (NiO) on indium tin oxide (ITO) substrates. These porous films outperformed corresponding compact films formed by continuous electrodeposition in terms of long-term stability. The maximum transmittance modulation of P-WO3 and P–NiO films were 57.0% and 52.1%, respectively, and changed insignificantly after 10,000 cycles, whereas C-WO3 and C–NiO films were degraded after 2500 and 1000 cycles, respectively. Not only does the porous morphology increases the electrochemical active surface area, but it also provides an efficient pathway for ion diffusion and charge transfer, resulting in fast kinetics, low resistance, high electro-activity, and excellent ion reversibility. This work will hopefully inspire more researchers to improve electrodeposition film fabrication and promote electrochromic device industrialization.

Electrochromic performance and potential stability of sputtered V2O5 film for a complementary inorganic all-solid-state electrochromic device

Vanadium Pentoxide (V2O5) has good ion storage capacity and weak anodic electrochromism. Since the V2O5 and Tungsten Trioxide(WO3) films were used as the auxiliary and major color-changing layers, respectively, then they were combined with heat-cured gel (LiClO4 + PC) + PMMA electrolyte as an complementary all-solid-state electrochromic device (ECD). Also, the V2O5 films were prepared at different oxygen flows and annealing temperatures. These results exhibited that oxygen flow of 4 sccm and annealing temperature of 400 °C can enable the optimal optical contrast (ΔT) to reach 38.7%@550 nm. The response time of the coloring(tc) and the bleaching(tb) were 5 and 4 s, respectively. Raman spectrum showed the stable phase of V5+ and specific element ratio of 2.52 and X-ray photoelectron spectroscopy (XPS) had the red shift phenomenon. However, the performance of ITO/V2O5/gel-electrolyte/WO3/ITO device, the best working voltage was measured as ±2.5 V, the optical contrast was ΔT = 42% and the response time of tc and tb were 6.5 and 5.5 s, respectively. These results demonstrate that ECD has the advantages of fast response time and low voltage stable startup.

Effects of additive and substrate on hydrogen sensing performances of sol-gel derived platinum doped tungsten trioxide gasochromic films

Tungsten trioxide is one of the most popular gasochromic materials whose color substantially changes upon exposure to hydrogen gas and is a key material for realizing various optical hydrogen gas sensors. However, it is still required to improve ease of film forming capability and manufacturing, which are also related to gasochromic performance. In the present study, platinum-doped tungsten trioxide (Pt/WO3) films were immobilized onto glass substrates by a sol-gel method, where acetylene-glycol surfactant (Surfynol 465) was investigated as a possible effective additive for the precursor solution. In the hydrogen exposure tests, the films fabricated on a fused-silica substrate and calcined at temperatures less than 350 °C showed weak but clear response characteristics and a high recovery rate because the Surfynol 465 surfactant also functioned as an effective reductant for the Pt precursor solution. The metallic state of Pt in the film calcined at low temperatures was confirmed by X-ray photoelectron spectroscopic analysis. However, the gasochromic performance was completely lost for the film fabricated on a soda-lime glass substrate and calcined at 500 °C. The results suggested that the poisoning effect is attributable to contamination of the film by sodium ions, which can leak from the glass substrate. The film prepared at a low calcination temperature of 350 °C did not suffer severe poisoning and responded to hydrogen gas.

Electron beam evaporated gold doped tungsten oxide nanostructured films for sensor applications

Gas sensors play a vital role in monitoring environmental pollution for human health, safety, and the detection of various gasses in the environment. Nanostructured metal oxide thin films have been widely used in sensor applications owing to their unique properties. In this study, pure and gold (Au) doped nanostructured tungsten trioxide (WO3) films were deposited on glass substrates by electron beam evaporation at room temperature. The microstructure of the WO3 films changed from nanoflakes to nanorods upon variation of the wt% of Au. The sensing properties of WO3 based nanostructure films were measured using a computer-controlled system. The gas sensing results showed that the Au-doped WO3 films exhibited a higher sensitivity than the undoped films. The 15 wt% Au-doped WO3 nanostructure films showed high sensitivity towards ethanol and the response (sensitivity) value was 89. The response and recovery times for 15 wt% Au-doped WO3 were 8 and 10 s, respectively.

Comparison of Electrodeposited and Sputtered Tungsten Trioxide Films for Inorganic Electrochromic Nanostructures

Electrochromic materials and their implementation with structural colors are currently being intensely researched because of their promising applications as non-emissive display devices utilizing ambient light. In particular, several fully inorganic devices that rely on electrochromic tungsten trioxide (WO3) have been presented. For preparing nanoscale films of this material, sputtering is the most established technique, but electrodeposition has recently been shown to be capable of achieving exceptionally high electro-optical modulation contrast without the need for expensive equipment. In this work, we investigate the possibilities of electrodeposited WO3 and present a systematic comparison with sputtered WO3 with respect to performance in electrochromic devices. Importantly, we show that “ultralarge” electro-optical modulation (∼95% change in transmission) is possible for both types of films. However, it is only the sputtered films that enable such high contrast in a stable electrolyte such as LiClO4 in propylene carbonate. The electrodeposited films are less uniform and difficult to make thicker than ∼500 nm. We find no evidence that the electrochromic properties of the electrodeposited WO3 are intrinsically better than those of sputtered WO3. However, the electrodeposited films are much rougher and/or porous on the nanoscale, which increases the switching speed considerably. We conclude that electrodeposited WO3 is mainly useful in applications in which high contrast is not essential while switching speed is. As an example, we present the first electrodeposited WO3 integrated with structural colors by sandwiching the material between two metal films. By electrical control, the reflective colors can then be tuned at least one order of magnitude faster (a few seconds) than previously reported while having fair color quality and without any loss of brightness.

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.

Tungsten trioxide film photoanodes prepared by aerosol pyrolysis for photoelectrochemical applications

The present work describes the preparation of tungsten trioxide photoanodes by aerosol pyrolysis on FTO/glass substrates. WO3 layers were characterised by profilometry, XRD, SEM and photoelectrochemistry (linear voltammetry and chronoamperometry under illumination). Optimal deposition conditions to obtain a relatively thick layer were found to be: 11 mm nozzle diameter, 2.5 cm nozzle to substrate distance, and 105 cm/s airflow velocity. A deposition temperature of at least 450 °C was necessary to obtain γ-monoclinic WO3. The as-deposited layers had loose particles on the surface; however, these particles could be removed by scotch tape with no influence on the roughness and photoactivity of the layer. The highest photocurrent was achieved by annealing the layers at 450 °C; however, such layers were not photoelectrochemically stable. To obtain superior long-term stability, an annealing temperature of 550 °C was necessary. The highest, stable photocurrent of ∼ 990 μA/cm2 (E = 0.9 V vs. Ag/AgCl, 1 sun) was achieved for a layer thickness of 3.8 µm.