Tungsten Oxide Nanorods Array and Nanobundle Prepared by Using Chemical Vapor Deposition Technique

Refractory Metals and Oxides for High-Temperature Structural Color Filters

Refractory metals have recently garnered significant interest as options for photonic applications due to their superior high-temperature stability and versatile optical properties. However, most previous studies only consider their room-temperature optical properties when analyzing these materials' behavior as optical components. Here, we demonstrate structural color pixels based on three refractory metals (Ru, Ta, and W) for high-temperature applications. We quantify their optical behavior in an oxygenated environment and determine their dielectric functions after heating up to 600 °C. We use in situ oxidation, a fundamental chemical reaction, to form nanometer-scale metal oxide thin-film bilayers on each refractory metal. We fully characterize the behavior of the newly formed thin-film interference structures, which exhibit vibrant color changes upon high-temperature treatment. Finally, we present optical simulations showing the full range of hues achievable with a simple two-layer metal oxide/metal reflector structure. All of these materials have melting points >1100 °C, with the Ta-based structure offering high-temperature stability, and the Ru- and W-based options providing an alternative for reversible color filters, at high temperatures in inert or vacuum environments. Our approach is uniquely suitable for high-temperature photonics, where the oxides can be used as conformal coatings to produce a wide variety of colors across a large portion of the color gamut.

Effect of Tungsten Oxide Nanostructures on Sensitivity and Selectivity of Pollution Gases

We report on the different surface structures of tungsten oxides which have been synthesized using a simple post-annealing-free hot-filament CVD technique, including 0D nanoparticles (NPs), 1D nanorods (NRs), and 2D nanosheet assemblies of 3D hierarchical nanoflowers (NFs). The surface morphologies, crystalline structures, and material compositions have been characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy, respectively. The sensor performances based on the synthesized samples of various surface morphologies have been investigated, as well as the influences of operating temperature and applied bias. The sensing property depends closely on the surface morphology, and the 3D hierarchical nanoflowers-based gas sensor offers the best sensitivity and fastest response time to NH₃ and CH₃ gases when operated at room temperature.

Tungsten oxide nanorod architectures as 3D anodes in binder-free lithium-ion batteries

Tungsten oxide nanorods were synthesized using a template assisted process. A polycarbonate membrane (pore diameter 100 nm) was vacuum infiltrated by an aqueous solution of ammonium paratungstate ((NH4)10H2W12O42·xH2O) and yielded crystalline 3D oriented WO3 nanorod arrays after template etching and calcination. By coating the nanorod arrays with carbon, a binder-free 3D WO3/C composite electrode could be fabricated, allowing capacities up to 1149, 811, 699, 559 and 253 mA h g-1 for cycles 1, 2, 20, 50 and 200 as well as a coulombic efficiency of around 99%. Moreover, as prepared WO3 nanorod structures without that specific type of carbon coating deliver capacities in a range of 200-250 mA h g-1 after 20 cycles. Finally, a full cell lithium ion battery system is fabricated. It consists of LiCoO2 nanoparticles as cathode and binder-free carbon coated 3D WO3 composite material as anode. Pre-lithiation of this 3D WO3/C composite material as pre-conditioning before full cell assembly leads to a cell capacity of almost twice of that without pre-lithiation. Discharge capacities of 111, 91, 41 and 23 mA h g-1 can be obtained for cycles 2, 20, 100 and 200 with a coulombic efficiency of around 99% in the case of the pre-lithiated 3D WO3/C composite anode.

Fabrication of hollow boron-doped diamond nanostructure via electrochemical corrosion of a tungsten oxide template

In the study, a hollow boron-doped diamond (BDD) nanostructure electrode is fabricated to increase the reactive surface area for electrochemical applications. Tungsten oxide nanorods are deposited on the silicon substrate as a template by the hot filament chemical vapor deposition (HFCVD) method. The template is coated with a 100 nm BDD layer deposited by HFCVD to form a core-shell nanostructure. The WO _x core is finally electrochemically dissolved to form hollow BDD nanostructure. The fabricated hollow BDD nanostructure electrode is investigated via scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The specific surface areas of the electrodes were analyzed and compared by using Brunauer-Emmett-Teller method. Furthermore, cyclic voltammetry and chronocoulometry are used to investigate the electrochemical characteristics and the reactive surface area of the as-prepared hollow BDD nanostructure electrode. A hollow BDD nanostructure electrode exhibits a reactive area that is 15 times that of a planar BDD thin electrode.

Synthesis of Tungsten Oxide Nanorod, Its Application on Textile Material, and Study of Its Functional Properties

Nanomaterial and its application in textiles are emerging as vast and diverse field due to enhanced functionalized characteristics. This study emphasizes the fabrication of tungsten trioxide nanostructured rods and analyzes its electrostatic and ultraviolet resistance properties. These nanorods are synthesized by hydrothermal method. Through hydrothermal method rod like nanostructures were grown on polyester fabric as it withstands curing temperature easily. The growth mechanism of the film is investigated. Electrostatic analysis of treated polyester fabric was failed but the analysis of seeded solution revealed that it has tunable transmittance modulation under different voltages and repetitive cyclic between the clear and blue states. Ultraviolet resistance of 100% seeded polyester fabric was higher than untreated fabric with respect to increasing concentration of nanorods. Results show that although the seeded solution is perfect, the conductivity of tungsten trioxide cannot be achieved on textiles.

Nanostructured Tungsten Oxide Composite for High-Performance Gas Sensors

We report the results of composite tungsten oxide nanowires-based gas sensors. The morphologic surface, crystallographic structures, and chemical compositions of the obtained nanowires have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman scattering, respectively. The experimental measurements reveal that each wire consists of crystalline nanoparticles with an average diameter of less than 250 nm. By using the synthesized nanowires, highly sensitive prototypic gas sensors have been designed and fabricated. The dependence of the sensitivity of tungsten oxide nanowires to the methane and hydrogen gases as a function of time has been obtained. Various sensing parameters such as sensitivity, response time, stability, and repeatability were investigated in order to reveal the sensing ability.

Single reactor deposition of silicon/tungsten oxide core–shell heterostructure nanowires with controllable structure and optical properties

Single reactor deposited crystalline Si/WO₃ core–shell nanowires showed superior optical absorption and enhanced photocurrent conversion.

Tungsten trioxide as a visible light photocatalyst for volatile organic carbon removal

Tungsten trioxide (WO₃) has been demonstrated to possess visible light photoactivity and presents a means of overcoming the UV-light dependence of photocatalysts, such as titanium dioxide. In this study, WO₃ nanostructures have been synthesised by a hydrothermal method using sodium tungstate (Na₂WO₄·2H₂O), sulphate precursors and pH as structure-directing agents and parameters, respectively. By altering the concentration of the sulphate precursors and pH, it was shown that different morphologies and phases of WO₃ can be achieved. The effect of the morphology of the final WO₃ product on the visible light photoactivity of ethylene degradation in the gas phase was investigated. In addition, platinum (Pt) was photodeposited on the WO₃ structures with various morphologies to enhance the photocatalytic properties. It was found that the photocatalytic properties of the WO₃ samples greatly depend on their morphology, chemical composition and surface modification. WO₃ with a cuboid morphology exhibited the highest visible light photoactivity compared to other morphologies, while adding Pt to the surface improved the performance of certain WO₃ structures.

Magnetic properties of corrosion-resistant CoW films

CoW films with different compositions have been prepared by an electrochemical deposition method.

Controlled growth of self-organized hexagonal arrays of metallic nanorods using template-assisted glancing angle deposition for superhydrophobic applications

The fabrication of controlled, self-organized, highly ordered tungsten and aluminum nanorods was accomplished via the aluminum lattice template-assisted glancing angle sputtering technique. The typical growth mechanism of traditional glancing angle deposition technique was biased by self-organized aluminum lattice seeds resulting in superior quality nanorods in terms of size control, distribution, and long range order. The morphology, size, and distribution of the nanorods were highly controlled by the characteristics of the template seeds indicating the ability to obtain metallic nanorods with tunable distributions and morphologies that can be grown to suit a particular application. Water wettability of hexagonally arranged tungsten and aluminum nanorods was studied after modifying their surface with 5 nm of Teflon AF 2400, as an example, to exhibit the significance of such a controlled growth of metallic nanorods. This facile and scalable approach to generate nano seeds to guide GLAD, with nano seeds fabricated by anodic oxidization of aluminum followed by chemical etching, for the growth of highly ordered nanorods could have significant impact in a wide range of applications such as anti-icing coating, sensors, super capacitors, and solar cells.

Formation of tungsten oxide nanostructures by laser pyrolysis: stars, fibres and spheres

In this letter, the production of multi-phase WO3 and WO3-x (where x could vary between 0.1 and 0.3) nanostructures synthesized by CO2-laser pyrolysis technique at varying laser wavelengths (9.22-10.82 mm) and power densities (17-110 W/cm2) is reported. The average spherical particle sizes for the wavelength variation samples ranged between 113 and 560 nm, and the average spherical particle sizes for power density variation samples ranged between 108 and 205 nm. Synthesis of W18O49 (= WO2.72) stars by this method is reported for the first time at a power density and wavelength of 2.2 kW/cm2 and 10.6 μm, respectively. It was found that more concentrated starting precursors result in the growth of hierarchical structures such as stars, whereas dilute starting precursors result in the growth of simpler structures such as wires.

Self Assembly and Properties of C:WO(3) Nano-Platelets and C:VO(2)/V(2)O(5) Triangular Capsules Produced by Laser Solution Photolysis

Laser photolysis of WCl(6) in ethanol and a specific mixture of V(2)O(5) and VCl(3) in ethanol lead to carbon modified vanadium and tungsten oxides with interesting properties. The presence of graphene's aromatic rings (from the vibrational frequency of 1,600 cm(-1)) together with C-C bonding of carbon (from the Raman shift of 1,124 cm(-1)) present unique optical, vibrational, electronic and structural properties of the intended tungsten trioxide and vanadium dioxide materials. The morphology of these samples shows nano-platelets in WO(x) samples and, in VO(x) samples, encapsulated spherical quantum dots in conjunction with fullerenes of VO(x). Conductivity studies revealed that the VO(2)/V(2)O(5) nanostructures are more sensitive to Cl than to the presence of ethanol, whereas the C:WO(3) nano-platelets are more sensitive to ethanol than atomic C.

Optimization, Yield Studies and Morphology of WO3Nano-Wires Synthesized by Laser Pyrolysis in C2H2and O2Ambients—Validation of a New Growth Mechanism

Laser pyrolysis has been used to synthesize WO₃nanostructures. Spherical nano-particles were obtained when acetylene was used to carry the precursor droplet, whereas thin films were obtained at high flow-rates of oxygen carrier gas. In both environments WO₃nano-wires appear only after thermal annealing of the as-deposited powders and films. Samples produced under oxygen carrier gas in the laser pyrolysis system gave a higher yield of WO₃nano-wires after annealing than the samples which were run under acetylene carrier gas. Alongside the targeted nano-wires, the acetylene-ran samples showed trace amounts of multi-walled carbon nano-tubes; such carbon nano-tubes are not seen in the oxygen-processed WO₃nano-wires. The solid–vapour–solid (SVS) mechanism [B. Mwakikunga et al., J. Nanosci. Nanotechnol., 2008] was found to be the possible mechanism that explains the manner of growth of the nano-wires. This model, based on the theory from basic statistical mechanics has herein been validated by length-diameter data for the produced WO₃nano-wires.