WO3 Thin Films Research Articles

Work function-tunable graphene/WO3 heterojunctions for high-performance photoelectrochemical cell: UV-treatment effect and defective graphene

Designing hybrid photoelectrodes with graphene capable of efficient charge-carrier transfer and excellent chemical stability is an effective strategy for developing high-performance photoelectrochemical (PEC) cells. However, it remains unclear how the PEC properties are enhanced and how to control the junction properties in graphene/metal oxide heterojunction-based photoelectrodes. Here, we develop a deterministic junction to enhance PEC performance in graphene/tungsten trioxide (WO3)-based photoelectrodes by tuning the work function of graphene. It reveals that the band structure of graphene/WO3 heterojunctions can be modified by ultraviolet (UV) treatment on WO3 thin films. This modification is supported by the observation that a single-layer graphene/UV-treated WO3 photoelectrode exhibits significantly enhanced PEC activities toward the oxygen evolution reaction (OER) (evidenced by features like a threefold increase in photocurrent, an onset potential shift, and improved stability), whereas the single-layer graphene/untreated WO3 electrode demonstrates improved properties for the hydrogen evolution reaction (HER). Additionally, defects in the graphene layer formed during PEC water splitting contribute to high catalytic activities of the graphene/WO3 photoelectrode due to a decrease in the Gibbs free energy for OER and HER. These results emphasize that band structure engineering via work function tuning in graphene/WO3 heterostructures can provide multiple benefits for high PEC performance and long-term stability.

Correlation of Structural Changes and Hydrogen Diffusion in Polycrystalline WO3 Thin Films by Combining In Situ Transmission Measurements and Raman Spectroscopy

AbstractDiffusion in polycrystalline tungsten trioxide (WO3) thin films is studied in a lateral geometry to better understand the impact of hydrogen‐induced structural phase transitions on the diffusion. WO3 thin films are coated with polymethylmethacrylate layer (PMMA). The latter is microstructured in such a way that a narrow stripe‐like gap occurs in the PMMA layer exposing the surface of the WO3 thin film. This stripe serves as the contact to the electrolyte in the intercalation experiment with hydrogen. After intercalation, the lateral diffusion of hydrogen inside WO3 below the PMMA layer can be observed, increasing the analyzable path and time scale by several orders of magnitude compared to the film thickness, thus, significantly improving spatial and temporal resolution of in situ transmission and Raman measurements. Spatially resolved transmission measurements in the wavelength range of 633±55 nm show that the diffusion process is dependent on hydrogen concentration and exhibits two regimes describable by different diffusion coefficients. Time‐resolved Raman spectroscopic measurements at different distances from the electrolyte contact area show that the switching between the two diffusion coefficients occurs at the phase transition from the orthorhombic to the tetragonal phase. The results are further supported by a simulation. The measurement approach is universally applicable for electrochromic films or multilayers.

Rapid thermal annealing treatment on WO3 thin films for energy efficient smart windows

Electrochromic devices (ECDs) based on tungsten trioxide (WO3) have garnered significant attention in the areas of smart windows, dynamic display, low-power displays, and in other advanced sectors. The electrochromic property of WO3 is primarily influenced by both electron conduction and ion diffusion processes. This research investigates on the influence of rapid thermal annealing (RTA) on the electrochromic performance of RF sputtered tungsten oxide thin films, which relies on ion diffusion process. RTA treated film showed a mixture of amorphous and crystalline (monoclinic), heterostructure phase. Structural, compositional, electrical, optical, morphological, and electrochromic studies were carried out using various techniques. Based on the electrochromic analysis, WO3 thin films, RTA treated at 300°C showed higher diffusion coefficient with larger optical modulation (ΔT) of 80 % due the formation of heterostructure with more oxygen vacancies. We hope that this research could propose the possibility for developing high-performance electrochromic smart windows.

Constructing an Al3+/Zn2+-Based Solid Electrolyte Interphase to Enable Extraordinarily Stable Al3+-Based Electrochromic Devices.

The interface between the electrochromic (EC) electrode and ionic conductor is crucial for high-performance and extraordinarily stable EC devices (ECDs). Herein, the effect of the ALD-AZO interfacial layer on the performance of the WO3 thin film was examined, revealing that an introduction of the ALD-AZO interfacial layer to the Al3+-based complementary ECDs can lead to improved EC performance and stability, such as an extraordinary cyclability of more than 20,000 cycles, an outstanding coloration efficiency of 109.69 cm2 C-1, and a maximum transmittance modulation of 63.44%@633 nm. The probable explanation is that the introduced ALD-AZO interfacial layer can effectively regulate the band gap of WO3, promote the electron transport process, and induce the formation of a robust solid electrolyte interphase to protect the electrode during cycling. These findings offer valuable insights for enhancing the EC performance of the EC thin films and new space for the construction of advanced multivalent Al3+-based ECDs.

Boron–doped WO3 thin films prepared using thermionic vacuum arc technique: physical properties

WO3 ince filmin fiziksel özelliklerinin iyileştirilmesi araştırmacılar arasında büyük ilgi görmektedir. Bu çalışmada, cam ve Silikon alttaşlar üzerine depolanan WO3 ince filmlerinin fiziksel özelliklerinin iyileştirilmesi için katkı maddesi olarak bor seçildi. Burada, farklı bor yüzdesine sahip filmlerin hazırlanmasında iyi bilinen plazma bazlı termiyonik vakum ark (TVA) tekniğinden yararlanılmıştır. Daha sonra, hazırlanan filmler uygun ölçüm cihazlarıyla karakterize edilir. Filmlerin pürüzlülüğü doğrudan bor miktarına ve alttaşların yapısına bağlıdır. Yapısal ölçüm, her iki alttaşta da WO3 fazlarının oluşumunu kanıtladı. Katkı miktarındaki artış, XRD desenlerindeki baskın tepe noktasında bir kaymaya neden olur. Filmlerin hesaplanan kristal boyutları 14 ila 49 nm arasında değişmektedir. Optik sonuçlara göre, WO3:B (%1) ve WO3:B (%3) filmlerinin optik bant aralığı (Eg) sırasıyla 3,23 ve 3,25 eV olarak elde edilmiştir. Borun artması filmlerin paketleme yoğunluğunun artmasına neden olur. Bu davranış alttaş özellikleriyle ilişkili değildir. Bu araştırma sonuçlarına bakıldığında, kristal boyutu ile daha düşük optik kayıp fonksiyonu arasında doğrudan bir ilişki vardır.

Fabrication of Tungsten Oxide Nanowalls through HFCVD for Improved Electrochemical Detection of Methylamine.

In this study, well-defined tungsten oxide (WO3) nanowall (NW) thin films were synthesized via a controlled hot filament chemical vapor deposition (HFCVD) technique and applied for electrochemical detection of methylamine toxic substances. Herein, for the thin-film growth by HFCVD, the temperature of tungsten (W) wire was held constant at ~1450 °C and gasification was performed by heating of W wire using varied substrate temperatures ranging from 350 °C to 450 °C. At an optimized growth temperature of 400 °C, well-defined and extremely dense WO3 nanowall-like structures were developed on a Si substrate. Structural, crystallographic, and compositional characterizations confirmed that the deposited WO3 thin films possessed monoclinic crystal structures of high crystal quality. For electrochemical sensing applications, WO3 NW thin film was used as an electrode, and cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were measured with a wide concentration range of 20 μM~1 mM of methylamine. The fabricated electrochemical sensor achieved a sensitivity of ~183.65 μA mM-1 cm-2, a limit of detection (LOD) of ~20 μM and a quick response time of 10 s. Thus, the fabricated electrochemical sensor exhibited promising detection of methylamine with considerable stability and reproducibility.

Enhanced structural, optical and electrical properties of polycrystalline WO3 thin films achieved by aluminum nanosheets coating

Herein the effects of aluminum nanosheets on the structural, morphological, optical and electrical properties of tungsten oxide thin films are reported. Polycrystalline phase of the thermally evaporated WO3 was achieved by the pulsed laser welding technique. The polycrystalline films are then coated with Al nanosheets of thicknesses of 100 nm and 150 nm by the ion coating technique. It is observed that Al induces the domination of the hexagonal structure of WO3 over the tetragonal. Associated with the enhanced crystallinity the light absorption in the films increased by more than 60% and the energy band gap narrowed significantly. Namely the energy band gap of the as grown WO3 decreased from 3.15 eV to 2.85 eV and 2.59 eV as the Al layer thickness increased from 100 to 150 nm, respectively. It is also observed that crystalline films of WO3 exhibited lower electrical resistivity compared to films fabricated by other techniques. The temperature dependent electrical resistivity measurement was carried out in the temperature range of 310–420 K. It showed room temperature values of 2.5 ( Ω cm), 2.2 ( Ω cm) and 1.9 ( Ω cm) and impurity levels centered at 0.25 eV, 0.34 eV and 0.16 eV for uncoated and films coated with Al nanosheets of thicknesses of 100 nm and 150 nm, respectively. The enhanced crystallinity that is accompanied with narrower energy band gap and lower electrical resistivity values make crystalline WO3 films promising for optoelectronic applications.

Effect of Oxygen Flow Rate, Post-annealing Temperature, and Different Electrolyte Concentrations on WO3 Thin Films Deposited by DC Magnetron Sputtering For Electrochromic Applications

Effect of Oxygen Flow Rate, Post-annealing Temperature, and Different Electrolyte Concentrations on WO3 Thin Films Deposited by DC Magnetron Sputtering For Electrochromic Applications

Effect of silver doping on the band gap tuning of tungsten oxide thin films for optoelectronic applications

In the cutting-edge world, semiconductor metal oxides usually tend to have a high optical band gap (>3.0 eV), significantly acceptable for potential optoelectronic applications. The present study discusses the synthesize of pristine tungsten trioxide (WO3) and Silver (Ag) doped WO3 (Ag: WO3) thin films onto a glass substrate at 450 °C, with varying concentrations of Ag doping (2, 4, 6, 8 and 10 at.%) using a simple Spray Pyrolysis Technique. Field emission scanning electron microscopy (FESEM) analysis showed the presence of particles in the WO3 and Ag: WO3 materials. The X-ray diffraction (XRD) pattern confirmed that the samples' hexagonal structure remained intact. In addition, Rietveld refinement was used for the samples to study the crystal structure meticulously. Because of the surface plasmon resonance effect, the samples' distinguishing characteristics were visible in their optical nature. For pristine WO3, the experimental band gap was determined to be 3.20 eV, and for varying doping concentrations, it was found to be 3.15 eV–2.90 eV, respectively. Furthermore, the fracture has remained imperceptible at elevated concentrations, resulting in a substantial influence on the optical characteristics of 10% Ag: WO3 thin films. The estimated redox potential for 2% Ag: WO3 shows a considerable influence of the band edge potential of the Conduction Band (CB) and Valance Band (VB). The activation energy was determined using temperature-dependent electrical resistivity and exhibited an ohmic nature. The synthesized material exhibited a negative temperature coefficient (NTC) effect at higher concentrations of doping, suggesting its potential applicability as a thermistor. A comprehensive analysis of this present study indicates that Ag can be a viable candidate for doping on WO3 thin films for use in optoelectronic devices.

Electrodeposited Tungsten Trioxide (WO3) Thin Films for Electrochromic Applications

The need of smart and innovative technology with energy saving approach is the main and serious concern while dealing with fastest growing urbanization and civilization. The smart technologies like electrochromic supercapacitors are beneficial in multifunctional way by providing energy storage systems with visual and reversible colour changes in many applications such as smart windows, electrochromic goggles, automotive mirrors, sunroofs, displays and so on. Herein, nanoporous WO3 thin film is prepared by using cathodic electrodeposition technique and used to study electrochromic as well as electrochemical properties. The bi-functionality of the electrode was confirmed by electrochemical tests including CV, GCD, EIS and chrono methods. The film shows greater coloration efficiency up to 52.61 cm2/C with an aerial capacitance 2.8 mF /cm2. Also, film shows faster switching kinetics as faster coloration and bleaching times like 1.88 and 2.6 s respectively. Hence, electrodeposited WO3 can be a good candidate for bi-functional electrochromic supercapacitors.

Improving Properties of Tungsten Oxide Films by Gamma Ray Irradiation

The deposition process and investigation of the physical properties of tungsten trioxide (WO3) thin films before and after gamma irradiation are presented in this paper. The WO3 thin films were deposited, using the pulse laser deposition technique, on glass substrates at laser energies of 600mJ and 800mJ. After deposition, the samples were gamma irradiated with Co60. The structural and optical properties of polycrystalline WO3 thin films are presented and discussed before and after 5kGy gamma irradiation at the two laser energies. X-ray diffraction spectra revealed that all the films consisted of WO3 crystallized in the triclinic form; the dislocation density and lattice strain increased with the absorbed dosage of gamma irradiation. The optical constants, the average diameter and the surface roughness of the WO3 films were calculated before and after gamma irradiation and for the two laser energies. It was found that the WO3 thin films conductivity increased by γ-irradiated and with the increase of the laser energy.

Highly responsive and selective NO gas sensing based on room temperature sputtered nanocrystalline WO3/Si thin films

This study investigates the nitric oxide (NO) gas sensing performance of room temperature sputtered nanocrystalline WO3 thin films deposited on Si substrate in a single step without heat treatment. The prepared WO3/Si sample properties have been systematically characterized for crystallographic, surface morphology, elemental, and chemical bonding analysis by XRD, FE-SEM, EDS, and XPS techniques, respectively. It has been observed that the thin film samples have a nanocrystalline structure with a granular-like porous morphology, and the presence of oxygen or metal vacancies/defects contributes to improving the sensing response of a target gas. The gas sensing performance of WO3 thin film deposited over Si (WO3/Si) has been recorded at various crucial parameters such as different operating temperatures (200–325 °C), gas concentrations (3–100 ppm), and target gases (H2S, CO, NH3, NO, and NO2). The maximum sensor response for 100 ppm concentration of NO gas was achieved at an operating temperature of 250 °C with a response time of ∼172 s and a recovery time of ∼86 s. At the optimal operating temperature of 250 °C, the lowest NO gas concentration was measured as low as 3 ppm. The calculated theoretical detection limit for NO gas at this concentration was determined to be 167 ppb. Further, the sample shows long-term stability over a period of 33 days and preserves the same value of sensor response. The selectivity performance tested for various gases clearly indicates that our sample is highly selective towards NO gas. This improved sensing performance can be attributed to the granular-like porous structure and excessive oxygen vacancies on the sample surface. The underlying sensing mechanism for superior response to NO gas has also been discussed. These results demonstrate the potential application of nanocrystalline WO3/Si thin film prepared at room temperature for the development of high-performance and cost-effective single-material-based metal oxide gas sensors.

Compositional Optimization of Sputtered WO3/MoO3 Films for High Coloration Efficiency.

Thin films of mixed MoO3 and WO3 were obtained using reactive magnetron sputtering onto ITO-covered glass, and the optimal composition was determined for the best electrochromic (EC) properties. A combinatorial material synthesis approach was applied throughout the deposition experiments, and the samples represented the full composition range of the binary MoO3/WO3 system. The electrochromic characteristics of the mixed oxide films were determined with simultaneous measurement of layer transmittance and applied electric current through the using organic propylene carbonate electrolyte cells in a conventional three-electrode configuration. Coloration efficiency data evaluated from the primary data plotted against the composition displayed a characteristic maximum at around 60% MoO3. Our combinatorial approach allows the localization of the maximum at 5% accuracy.

Effect of Nd substitution on electronic, thermoelectric, and optical response of WO3

The properties of Nd-doped WO3 thin films are studied to assess their suitability for photovoltaic and optoelectronic applications. The simulations on pristine and Nd-doped WO3 were performed using Tran Blaha modified Becke-Johnson approximation to explore the various properties, whereas the spin coating technique was employed to synthesize thin films. X-ray diffraction analysis revealed the crystalline cubic structure in all synthesized thin films. The morphology contains uniform rod-like features and the width of these were enhanced in doped composition. The projected density of states demonstrated the major prominent contributions of W-d in conduction and O-p in the valence band while Nd-f orbital plays a major contribution in doped compositions. Thermoelectric parameters were found to change significantly with Nd incorporation in WO3. The highest refractive index and real epsilon values were recorded at the higher energy regimes approximately 2.96 and 8.61, respectively, for compositions containing maximum dopant content. The optical conductivity and absorption coefficient showed an enhanced trend in doped composition which is considered favourable for improved optoelectronic and photovoltaic applications. The experimental band gap of WO3 was calculated as 2.03 eV and found to decrease with increment of Nd doping concentration.

Methodical tuning of NH3 gas sensing in WO3 thin films by electron beam irradiation

The present work focuses on the structure, morphology, optical and sensing analysis of Electron Beam Irradiation (EBI) treated WO3 films synthesized by the spray pyrolysis technique. X-ray diffraction (XRD) revealed a slight shift in the 2θ position, indicating stress generated due to EBI process. Scanning Electron Microscopy (SEM) morphographs presented well-defined grains at higher irradiation dosages. X-ray Photoelectron Spectroscopy (XPS) studies showed increased oxygen vacancy defects for the 5 kGy treated sample compared to unirradiated WO3. Sensing analysis of unirradiated and EBI-treated films was conducted towards ammonia (NH3) at an optimum operating temperature of 200 °C. Sensor response of 5 kGy treated film increased by − 4.5 fold compared to unirradiated film at 5 ppm NH3 concentration. The current study demonstrates the importance of EBI in tailoring the NH3 sensing properties of WO3 films.

Enhanced Photoelectrochemical Performance Using Cobalt-Catalyst-Loaded PVD/RF-Engineered WO3 Photoelectrodes

Critical to boosting photoelectrochemical (PEC) performance is improving visible light absorption, accelerating carrier separation, and reducing electron–hole pair recombination. In this investigation, the PVD/RF method was employed to fabricate WO3 thin films that were subsequently treated using the surface treatment process, and the film surface was modified by introducing varying concentrations of cobalt nanoparticles, a non-noble metal, as an effective Co catalyst. The results show that the impact of loaded cobalt nanoparticles on the film surface can explain the extended absorption spectrum of visible light, efficiently capturing photogenerated electrons. This leads to an increased concentration of charge carriers, promoting a faster rate of carrier separation and enhancing interface charge transfer efficiency. Compared with a pristine WO3 thin film photoanode, the photocurrent of the as-prepared Co/WO3 films shows a higher PEC activity, with more than a one-fold increase in photocurrent density from 1.020 mA/cm2 to 1.485 mA/cm2 under simulated solar radiation. The phase, crystallinity, and surface of the prepared films were analysed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The PVD/RF method, scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) were employed to assess the surface morphology of the fabricated film electrode. Optical properties were studied using UV–vis absorbance spectroscopy. Simultaneously, the photoelectrochemical properties of both films were evaluated using linear sweep voltammetry and electrochemical impedance spectroscopy (EIS). These results offer a valuable reference for designing high-performance photoanodes on a large scale for photoelectrochemical (PEC) applications.

Investigation on the optical and electrochromic characteristics of thin films of WO3 doped with graphene and MXene (Ti2AlC)

In the paper, optical, electrochromic, surface, and microstructural properties have been investigated to determine the properties of WO3 material doped with graphene and MXene. It was observed that the crystallite size and dimensions were small according to the analyses. When graphene and MXene were added to WO3, the band gap values shifted to a higher energy level. 2D material peak positions were assigned to Raman shift spectra analyses. Microstructural variations were observed into X-Ray diffraction patterns. MXene peaks for XRD were determined at approximately 30°. Current density-voltage measurements were obtained at 20, 40, 80, and 160 mV/s, and clear oxidation and reduction peaks were observed. Cathodic peaks of 2D material-doped WO3 were observed at approximately −1.2 V and the positions of anodic peaks can be altered depending on the type of 2D material. For graphene, the anodic peak occurs at −0.7 V and −0.1 V after MXene doping. 2D materials increased the diffusion coefficient of undoped WO3 by about 100–1000 times. The intercalation charge amount of WO3 material doped with 2D is more than 10–20 times greater than the undoped sample. It was found that graphene and MXene improved various properties of the sample.

Improved cyclic durability and chemical stability of WO3 thin films by incorporation of Nb2O5

To achieve commercial smart windows operating in environments exposed to air and moisture with a hot weather, there has been a steady demand for large-area electrochromic thin films with high cyclic durability and chemical stability. In this article, we discuss the change in the electrochromic performance of WO3 thin films through incorporation of Nb2O5, which is stable against an acid electrolyte and heated water. With the increase in the content of Nb2O5 achieved by increasing the sputtering power, the charge density and transmittance modulation gradually decreased, while the cyclic durability was noticeably improved. When the as-deposited WO3 thin films were soaked in water at 70 °C, their flat surface and electrochromic properties degraded significantly. Conversely, the deterioration of the surface morphology of the Nb2O5-incorporated WO3 thin films after etching in the heated water was alleviated, which led to electrochromic performances on par with those of the unetched films. This is an effective approach for manufacturing of electrochromic devices with an enhanced stability to prevent structural degradation under hot and humid conditions.

Domain structures in ferroelectric epitaxial WO3 thin films

Domain structures in ferroelectric epitaxial WO3 thin films

Low-temperature open-atmosphere growth of WO3 thin films with tunable and high-performance photoresponse

In-situ orientation tuning of WO3 thin films with high crystallinity is achieved with a low-temperature and open-atmosphere deposition technique. The fabricated devices showed a significant change in photo-response for film orientation.