WO3 Target Research Articles

Sputter-grown Eu-doped WO3-Eu2(WO4)3 composite red phosphor thin films

Eu3+-activated WO3-Eu2(WO4)3 luminescent composite thin films are grown on low-cost slide glass substrates by radio frequency sputtering and then annealing in an air atmosphere furnace. The films obtained by sputtering 12 at.% of Eu-added WO3 target afforded a two-phase composite structure comprising Eu-doped WO3 and Eu2(WO4)3 after annealing. The composite thin films annealed at 600 °C exhibited strong red emission after growing at room temperature compared to those annealed at 500 °C under the excitation of 254, 394, and 465 nm corresponding to ultraviolet, near-ultraviolet, and blue light, respectively. The thin films grown at low temperatures without annealing did not emit under ultraviolet light. The crystalline structure, surface morphology, and optical properties, such as transmittance and photoluminescence, of the films grown at 500 °C were almost similar to those of the thin films grown at room temperature when they were annealed at the same temperature. Pure WO3 thin films without Eu doping showed similar crystallization behavior under the same annealing conditions as Eu-added composite films; however, they did not exhibit photoluminescence properties. Our report on the integration of thin-film red phosphors on glass substrates is promising for the development of low-cost and large-area optical devices activated at various excitation wavelengths.

Tungsten-Based Cost-Effective Gas Sensors for H2S Detection

Tungsten trioxide thin films were deposited on silicon substrates by non-reactive RF sputtering from a WO3 target at room temperature. The WO3 films were post-annealed at two different temperatures, 400 °C and 500 °C. The morphological and microstructural properties of these films were analyzed by using atomic force microscopy and X-ray diffraction. X-ray diffraction patterns only show WO3 oxide phases. The AFM images show different morphologies with smaller grains for the film annealed at 400 °C. WO3 sensing films and W heating elements were embedded in commercial cases for the fabrication of cost-effective gas sensors. The sensitivity and dynamic response of the sensors were analyzed under various concentrations of H2S, from 20 to 100 ppm, at SIMTRONICS SAS (3M Company, Saint Paul, MN, USA). A good sensitivity G/G0 of about 6.6 under H2S 100 ppm was obtained with the best sensor. An interesting dynamic response was observed in particular with a short response time. Additionally, the evolution of the sensitivity was studied, and a conduction model was proposed for explaining the conduction mechanism under H2S exposition.

Pulsed Laser Deposition of Nanostructured MoS3/np-Mo//WO3-y Hybrid Catalyst for Enhanced (Photo) Electrochemical Hydrogen Evolution.

Pulsed laser ablation of MoS2 and WO3 targets at appropriate pressures of background gas (Ar, air) were used for the preparation of new hybrid nanostructured catalytic films for hydrogen production in an acid solution. The films consisted of a nanostructured WO3−y underlayer that was covered with composite MoS3/np-Mo nanocatalyst. The use of dry air with pressures of 40 and 80 Pa allowed the formation of porous WO3−y films with cauliflower- and web-like morphology, respectively. The ablation of the MoS2 target in Ar gas at a pressure of 16 Pa resulted in the formation of amorphous MoS3 films and spherical Mo nanoparticles. The hybrid MoS3/np-Mo//WO3−y films deposited on transparent conducting substrates possessed the enhanced (photo)electrocatalytic performance in comparison with that of any pristine one (MoS3/np-Mo or WO3−y films) with the same loading. Modeling by the kinetic Monte Carlo method indicated that the change in morphology of the deposited WO3−y films could be caused by the transition of ballistic deposition to diffusion limited aggregation of structural units (atoms/clusters) under background gas pressure growth. The factors and mechanisms contributing to the enhancement of the electrocatalytic activity of hybrid nanostructured films and facilitating the effective photo-activation of hydrogen evolution in these films are considered.

Reactive co-sputtering of tungsten oxide thin films by glancing angle deposition for gas sensors

Tungsten oxide thin films exhibiting an oriented columnar architecture were prepared by reactive co-sputtering. Two opposite W and WO3 targets focused on the center of the substrate were simultaneously sputtered using opposite and oblique angles of 80° from the substrate normal. The reactive gas pulsing process was used to adjust the films electrical resistivity. Different inclined columnar structures were produced and applied as gas sensors for dodecane detection. Morphology, structure and resistivity of the films were investigated and connected to the sensing performances measured from 373 to 773 K.

Deuteron irradiation of W and WO3 for production of high specific activity 186Re: Challenges associated with thick target preparation

This investigation evaluated target fabrication and beam parameters for scale-up production of high specific activity 186Re using deuteron irradiation of enriched 186W via the 186W(d,2n)186Re reaction. Thick W and WO3 targets were prepared, characterized and evaluated in deuteron irradiations. Full-thickness targets, as determined using SRIM, were prepared by uniaxially pressing powdered natural abundance W and WO3, or 96.86% enriched 186W, into Al target supports. Alternatively, thick targets were prepared by pressing 186W between two layers of graphite powder or by placing pre-sintered (1105°C, 12h) natural abundance WO3 pellets into an Al target support. Assessments of structural integrity were made on each target prepared. Prior to irradiation, material composition analyses were conducted using SEM, XRD, and Raman spectroscopy. Within a minimum of 24h post irradiation, gamma-ray spectroscopy was performed on all targets to assess production yields and radionuclidic byproducts. Problems were encountered with the structural integrity of some pressed W and WO3 pellets before and during irradiation, and target material characterization results could be correlated with the structural integrity of the pressed target pellets. Under the conditions studied, the findings suggest that all WO3 targets prepared and studied were unacceptable. By contrast, 186W metal was found to be a viable target material for 186Re production. Thick targets prepared with powdered 186W pressed between layers of graphite provided a particularly robust target configuration.

Studies on Electrochromic Properties of RF Sputtered Vanadium Oxide: Tungsten Oxide Thin Films

Among the transition metal oxides, Tungsten Oxide (WO3) is the most widely used electrochromic material for smart window applications. Tungsten oxide thin films can be modified by mixing V2O5 in various proportions to achieve neutral coloring. In the present work, influence on structural, optical, surface morphological and electrochromic properties by mixing of V2O5 with WO3 has been studied. V2O5 mixed WO3 targets of various compositions were prepared and homogeneity of those targets was confirmed through powder X-ray diffraction. Thin films were prepared by RF magnetron sputtering method using Corning glass as substrates with 100W as RF power at room temperature. The as-deposited films were found as amorphous with good adhesion to the substrate. Laser Raman studies confirmed this amorphous nature. Neutral coloration was achieved with low amount of mixing of V2O5 with WO3. Room temperature photoluminescence characterizations revealed the presence of strong emissions in the near UV (375nm) and blue (418nm) regions when excited at 275nm. Electrochemical cation intercalation was promoted using 0.05M H2SO4. Electrochromic parameters such as response time, diffusion constants, reversibility and coloration efficiency were calculated from the electrochromical and iono-optical studies like chronoamperometry and chronocoulometry.

Nanostructure catalysts prepared by multi-sputtering deposition process for enhanced methanol electrooxidation reaction

We report size and/or composition-controlled nanostructure catalysts for direct methanol fuel cells fabricated by means of multi-sputtering deposition process. The size-controlled Pt nanophases ranging from 0.62±0.14nm to 3.07±0.34nm in average size with narrow size distribution are fabricated as a function of sputtering power ratio of targets. The composition-controlled PtRu alloy nanophases deposited at different RF power ratio of Pt and Ru targets with the same power of WO3 target exhibit varied atomic percentages of PtRu, i.e. (79.8:21.2), (62.2:37.8) and (37.6:62.4). Furthermore, the PtRu nanophases deposited at a constant RF power ratio of Pt and Ru targets with different power of WO3 target show controlled average sizes such as 3.62±0.15nm, 1.86±0.23nm, and 1.20±0.22nm with the same compositions. The specific maximum power density of the nanostructure catalyst (∼100Wg−1) is superior to that of the conventional nanostructure catalyst (∼37Wg−1), representing that the nanostructure catalyst has an excellent electrode structure for methanol electrooxidation as compared to the conventional catalyst.

Thin Transparent W-Doped Indium-Zinc Oxide (WIZO) Layer on Glass

Annealing effect on structural and electrical properties of W-doped IZO (WIZO) films for thin film transistors (TFT) was studied under different process conditions. Thin WIZO films were deposited on glass substrates by RF magnetron co-sputtering technique using indium zinc oxide (10 wt.% ZnO-doped In2O3) and WO3 targets in room temperature. The post annealing temperature was executed from 200 degrees C to 500 degrees C under various O2/Ar ratios. We could not find any big difference from the surface observation of as grown films while it was found that the carrier density and sheet resistance of WIZO films were controlled by O2/Ar ratio and post annealing temperature. Furthermore, the crystallinity of WIZO film was changed as annealing temperature increased, resulting in amorphous structure at the annealing temperature of 200 degrees C, while clear In2O3 peak was observed for the annealed over 300 degrees C. The transmittance of as-grown films over 89% in visible range was obtained. As an active channel layer for TFT, it was found that the variation of resistivity, carrier density and mobility concentration of WIZO film decreased by annealing process.

Electrochromic Nb-doped WO3 films: Effects of post annealing

The Nb-doped WO3 films were deposited by e-beam co-evaporation method using ceramic WO3 targets and metal Nb slugs. The films were analyzed by glancing incident angle X-ray diffraction (GIAXRD), UV/visible spectrophotometer, electrochemical cyclic voltammetry, X-ray photoelectron spectroscopy (XPS). The as-prepared film is brown and amorphous in structure. The film has low transmission in optical visible region. The XPS results indicate that the as-deposited film is non-stoichiometric. By applying a negative potential, the as-deposited film does not show obvious electrochromic effect. However, the electrochromic properties of Nb-doped WO3 films are improved by post annealing treatment at 350, 400, and 450°C in oxygen atmosphere. The Nb-doped WO3 films transform into crystalline structure and become transparent after post annealing treatment. The energy band gap, optical modulation, and color efficiency increase with annealing temperature.

Tunable optical and nano-scale electrical properties of WO3 and Ag-WO3 nanocomposite thin films

WO3 and Ag-WO3 nanocomposite thin films have been synthesized from pure WO3 and Ag-WO3 composite pressed powder targets submitted to pulses generated by a frequency quadrupled Nd:yttrium aluminium garnet (YAG; λ = 266 nm, τ ~ 5 ns, ν = 10 Hz) laser source. The irradiations were performed in low pressure oxygen atmosphere. The obtained results proved the possibility to tailor the synthesized thin films optical properties in the UV–Visible spectral region and their nano-scale electrical characteristics through the process parameters, as ambient oxygen pressure value during the thin films deposition and Ag concentration of the Ag-WO3 composite targets. The tunable optical and electrical features allow for the creation of new materials for future applications as photocatalysts, transparent conducting electrodes, electrochromic or chemical and biological sensor devices.

Investigation of the impurity concentrations and product activities of some targets used in radioisotope production: a neutron activation analysis study

Neutron activation analysis using the k0 standardization method (k0-NAA) and fast neutron activation analysis using reactor fission neutrons, were used to determine the impurity concentrations in WO3, MoO3, SnO2 and TeO2 targets. The radioimpurities 124Sb, 134Cs, 60Co, 87Rb, 182Ta, 233Pa, 65Zn, 59Fe, 110mAg, 51Cr, 95Zr, 75Se and 114mIn were found in the irradiated targets and their origin either neutron capture reactions, or threshold reactions or both were identified. The specific activities of 187W, 188Re, 99mTc, 113mIn, 117mSn and 131I radioisotopes were determined. It is shown that the epithermal neutron flux significantly contributes to the isotopes characterized with high Q0 values. It is shown that the 117mSn isotope can be produced with a high specific activity using the fast neutron component of the reactor neutron spectrum.

Spectroscopic Characteristics of Plasma Plume Induced by Laser Ablation of WO3 Target

Spectroscopic Characteristics of Plasma Plume Induced by Laser Ablation of WO3 Target

Structural Stability and Phase Transitions in WO3 Thin Films

Tungsten oxide (WO3) thin films have been produced by KrF excimer laser (lambda = 248 nm) ablation of bulk ceramic WO3 targets. The crystal structure, surface morphology, chemical composition, and structural stability of the WO3 thin films have been studied in detail. Characterization of freshly grown WO3 thin films has been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurements. The results indicate that the freshly grown WO3 thin films are nearly stoichiometric and well crystallized as monoclinic WO3. The surface morphology of the resulting WO3 thin film has grains of approximately 60 nm in size with a root-mean-square (rms) surface roughness of 10 nm. The phase transformations in the WO3 thin films were investigated by annealing in the TEM column at 30-500 degrees C. The phase transitions in the WO3 thin films occur in sequence as the temperature is increased: monoclinic --> orthorhombic --> hexagonal. Distortion and tilting of the WO6 octahedra occurs with the phase transitions and significantly affects the electronic properties and, hence, the electrochemical device applications of WO3.

Particle induced X-ray emission spectroscopic (PIXE) and surface morphological (AFM) studies on electron beam evaporated WO3 thin films

The present work is concerned with tungsten oxide (WO3) thin films, which feature strongly in electrochromic applications. The films were deposited on glass substrates and fluorine doped tin oxide (FTO) coated glass substrates by the electron beam evaporation technique using a WO3 target. The elemental analysis of the films was performed by particle induced X-ray emission (PIXE) spectroscopy, and the surface morphology of the films was studied using atomic force microscopy (AFM). To the best of our knowledge, this is the first time that PIXE has been used for the analysis of elements present in electron beam evaporated WO3 films. In this study, PIXE was applied to confirm the presence of constituent element in the films. Atomic force microscopic studies revealed that the deposited WO3 films are homogeneous, crack-free surfaces with uniform spherical nanograins. These characterisation studies were carried out for the films prepared on different substrates, and at different deposition temperatures and annealing temperatures. The increase in cluster size with increasing substrate temperature can be explained by the increased diffusion kinetics of the neighbouring particles and/or clusters in the film, causing them to coalesce to form a dense surface coating. This would provide a better understanding of the electrochemical behaviour of the films.

パルスレーザー堆積法により作製したＷＯ３光記録膜（２）

Tungsten oxide films were deposited on glass substrates (Corning #7059) and polycarbonate substrates by a pulsed laser deposition technique using the both targets WO3 and WO2. At this time, the difference in the transmittance, ΔT, between the annealed state and the as-deposited state of the films fabricated with WO2 target was about 70% at the wavelength of 400 nm and that of the films prepared with the WO3 target was about 60%. From XRD spectra and XPS spectra, it was found that the as-deposited state was an oxygen-deficient amorphous state and the crystalline state was caused by absorbing oxygen through the annealing process (at 500°C×10 min).It was confirmed from the revolution-test of the disc structure that the values of CNR obtained at the write peak power 7.5∼9 mW was more than 50∼60 dB. From SEM images of top the view, it was presumed that a recording mechanism was related to a cooperative effect of the reflectivity change and the volume change induced in the recorded dot.

Sputter deposition of tungsten trioxide for gas sensing applications

Tungsten trioxide thin films were grown by reactively sputtering a circular WO3 target in different Ar–O2 atmospheres. After deposition, data on the structural, optical and electrical properties were obtained by using transmission electron microscopy (TEM) to examine the structure and the morphology of the films, UV-VIS spectrophotometry to determine optical absorption edge characteristics, and Hall effect measurements to determine the change carrier mobility and the film resistivity. In addition, the film resistance variations in controlled atmospheres were examined and the gas sensing properties of films grown under different conditions were compared. The aim of the study was to examine the effect of O2 concentration in the sputtering atmosphere on structural, optical, electrical and sensing properties. © 1998 Kluwer Academic Publishers

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

Abstract 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.

Electrochromic properties of rf-sputtered tungstic oxide film prepared from a W metal target

Tungstic oxide film is prepared from a W metal target by the rf sputtering method and its electrochromic characteristics are compared with that from WO3 target. Maximum coloration efficiency found for both kinds of films are equal and about 0.06 cm2 /mC at the wavelength of 600 nm, which is higher than that of typical evaporated films. Films from the W metal target, for the maximum coloration efficiency, can be prepared at a broader oxygen range of sputtering atmosphere than that of a WO3 target. It is found that films from a W metal target can be prepared at higher input power than that of a WO3 target. Therefore, the W metal target is suitable to get films with required thickness and EC characteristics.

Preparation and aging of sputtered tungstic oxide films

Conditions for the preparation of electrochromic tungstic oxide films with high efficiency for coloration have been investigated. Tungstic oxide films were deposited on glass substrates by rf sputtering in Ar-O2 mixture from a compressed powder WO3 target. As-deposited films require an ‘‘aging process,’’ in which the density of charges extracted in bleaching is smaller than that injected in coloring. It is considered that a part of the protons introduced during the aging combine with bonds of unstable oxygen contained in the as-deposited films. After the aging period, sputtered films have reversible coloration and bleaching cycles. Maximum electrochromic coloration efficiencies are 0.09 and 0.04 cm2/mC at wavelengths of 800 and 500 nm, respectively. They are obtained when the sputtering atmosphere is 0.04–0.05-Torr total pressure and 5% oxygen content. At any rate, substrate temperature should be kept at 100 °C or less.

ChemInform Abstract: pH‐Sensitive WO3‐Based Microelectrochemical Transistors.

AbstractWO3 is deposited on an array of closely spaced (1.2 μm) Au or Pt microelectrodes (∼ 2 · 50 · 0.1 μm) by rf sputtering of a polycrystalline WO3 target.