Photocorrosion stable WO3 nanowire arrays are synthesized by a solvothermal technique on fluorine-doped tin oxide coated glass. WO3 morphologies of hexagonal and monoclinic structure, ranging from nanowire to nanoflake arrays, are tailored by adjusting solution composition with growth along the (001) direction. Photoelectrochemical measurements of illustrative films show incident photon-to-current conversion efficiencies higher than 60% at 400 nm with a photocurrent of 1.43 mA/cm2 under AM 1.5G illumination. Our solvothermal film growth technique offers an exciting opportunity for growth of one-dimensional metal oxide nanostructures with practical application in photoelectrochemical energy conversion.

Vertically Aligned WO3 Nanowire Arrays Grown Directly on Transparent Conducting Oxide Coated Glass: Synthesis and Photoelectrochemical Properties

We developed a postgrowth modification method of two-dimensional WO3 nanoflakes by a simultaneous solution etching and reducing process in a weakly acidic condition. The obtained dual etched and reduced WO3 nanoflakes have a much rougher surface, in which oxygen vacancies are created during the simultaneous etching/reducing process for optimized photoelectrochemical performance. The obtained photoanodes show an enhanced photocurrent density of ∼1.10 mA/cm2 at 1.0 V vs Ag/AgCl (∼1.23 V vs reversible hydrogen electrode), compared to 0.62 mA/cm2 of pristine WO3 nanoflakes. The electrochemical impedance spectroscopy measurement and the density functional theory calculation demonstrate that this improved performance of dual etched and reduced WO3 nanoflakes is attributed to the increase of charge carrier density as a result of the synergetic effect of etching and reducing.

WO3 Nanoflakes for Enhanced Photoelectrochemical Conversion

The morphology-controlled synthesis and near-infrared (NIR) absorption properties of W18O49 were systematically investigated for the application of innovative energy-saving windows. Various morphologies of W18O49, such as nanorods, nanofibers, nanograins, nanoassembles, nanoplates, and nanoparticles, with various sizes were successfully synthesized by solvothermal reactions using organic alcohols as reaction media and WCl6, W(EtO)6, and WO3 solids as the tungsten source. W18O49 nanorods of less than 50 nm in length showed the best optical performance as an effective solar filter, which realized high transmittance in the visible region as well as excellent shielding properties of NIR light. Meanwhile, the W18O49 nanorods also exhibited strong absorption of NIR light and instantaneous conversion of the absorbed photoenergy to the local heat.

Morphology-controlled synthesis of W18O49 nanostructures and their near-infrared absorption properties.

A monoclinic tungsten trioxide nanowire array has been grown on silicon substrates using tungsten powders as source materials by thermal evaporation under specific synthesis conditions (1000 °C, 13–15 Torr, 200 sccm air flow). The morphology, chemical composition and crystal structure of the as-prepared tungsten trioxide nanowires were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and transmission electron microscopy. The nanowires were identified as monoclinic in structure, with diameters ranging from 40 to 100 nm and lengths up to 5 µm. It was found that sufficient oxygen and air flow are the major factors to influence the nanowire array growth. The nanowire array was employed directly for gas sensor fabrication using photolithography. The gas sensing experiments revealed that the nanowire array sensors are highly sensitive to NO2 (50 ppb), making the tungsten trioxide nanowire array a competitive candidate for highly sensitive gas sensor fabrication.

Growth of monoclinic WO3nanowire array for highly sensitive NO2 detection

https://home.iitk.ac.in/~ashutos/2012-publicaions/CARBON%202012_PAN%20CNT%20nanowire_Tanmoy.pdf

Improved graphitization and electrical conductivity of suspended carbon nanofibers derived from carbon nanotube/polyacrylonitrile composites by directed electrospinning

The self-synthesis of tungsten oxide (W18O49) nanowires on sputter-deposited WCx films using a simple annealing/oxidization process was reported. It was found that thermal annealing of WCx films at 680°C for 30min in nitrogen followed by oxidation at 450°C for 30min in pure oxygen would yield dense and well-crystallized monoclinic W18O49 (010) nanowires with a typical length/diameter of about 0.15–0.2μm∕10–20nm. The formation of W18O49 nanowires is attributed to the nuclei of immature W2C nanowires experiencing a regrowth process, accompanied by carbon depletion and the oxidization of tungsten during the subsequent oxidization process.

/pdf/preparation-of-tungsten-oxide-nanowires-from-sputter-400fu0xp3l.pdf

Preparation of tungsten oxide nanowires from sputter-deposited WCx films using an annealing/oxidation process

Large-area (0.6 ×0.6 and 1 ×1 mm2) highly-efficient GaN-based light-emitting diodes (LEDs) with a vertical-conducting structure (VM-LEDs), using a patterned laser lift-off technique and a Ni electroplating process as well as a surface treatment of the top n-GaN epilayer by plasma and chemical etching, were successfully fabricated and investigated. Compared to regular LEDs of the same size, both the forward voltage drop and the light output power (Lop) of the VM-LED were substantially improved. With inductively coupled plasma (ICP) etching followed by an additional KOH etching and an HF/HCl treatment on the n-GaN layer, an increase in Lop by 227% (195%) at 350 (800) mA has been achieved for the (1 ×1 mm2)-sized VM-LEDs.

https://iopscience.iop.org/article/10.1143/JJAP.45.3436/pdf

Effect of Surface Treatment on the Performance of Vertical-Structure GaN-Based High-Power Light-Emitting Diodes with Electroplated Metallic Substrates

The self-synthesis of tungsten oxide (W18O49) nanowires/nanosheets on sputtering-deposited tungsten films was obtained by thermal annealing in nitrogen under the thermal budgets of 750 °C for ≥2 h or ≥850 °C for 0.5 h. Experimental evidence of the nanomorphology transformation of tungsten oxide nanostructures from nanowires to nanosheets was presented, which can be attributed to the formation and re-crystallization of an amorphous interface layer between two neighboring parallel-growth nanowires linked together with a low angle misalignment along their growth directions.

The evolution of tungsten oxide nanostructures from nanowires to nanosheets

In this work, the fabrication of gas sensors utilizing self-synthesized tungsten oxide nanowires (TONWs) and their response to NO2 are reported. The gas sensor is based on a sputter-deposited WCx/SiO2/WCx triple-layer structure with the periphery of the SiO2 layer etched chemically. Self-synthesized TONWs with crystalline W18O49(010) were grown by simple thermal annealing in nitrogen ambient, which linked, in parallel, the upper and lower WCx electrodes for gas sensing. The TONW-based sensors increased in resistance in NO2 because the surface of TONWs comprised oxygen adsorbates and the adjacent space charge region was electron-depleted. The amount of enlargement in resistance increased with increasing temperature. To improve the detectability of the parallel-connected TONW-based sensor, a connection of several individual sensors in series was proposed to enlarge the number of TONWs for gas sensing. For the 8-series-connected sensor, a sensitivity as high as 9.3, a response time as low as about 9 s, and a detectability as low as 2 ppm for NO2 were obtained.

https://iopscience.iop.org/article/10.1143/JJAP.47.3272/pdf

Development of Gas Sensors Based on Tungsten Oxide Nanowires in Metal/SiO2/Metal Structure and Their Sensing Responses to NO2

In this work, the design and fabrication of Au/n-Si Schottky barrier diodes (SBDs) with various edge termination schemes including a reduce surface field (RESURF) type lateral super-junction (LSJ), polysilicon (poly-Si) floating, and guard rings are presented. A novel method using ion implantation through a poly-Si film for guard ring fabrication is proposed to prevent damage to the silicon surface. Experimental results show that the reverse leakage current of the proposed SBDs is reduced by about two orders and the breakdown voltage is increased by more than 4-fold those of conventional SBDs.

https://iopscience.iop.org/article/10.1143/JJAP.44.L1244/pdf

Bor Wen Liou

Papers

Preparation of tungsten oxide nanowires from sputter-deposited WCx films using an annealing/oxidation process

Effect of Surface Treatment on the Performance of Vertical-Structure GaN-Based High-Power Light-Emitting Diodes with Electroplated Metallic Substrates

The evolution of tungsten oxide nanostructures from nanowires to nanosheets

Development of Gas Sensors Based on Tungsten Oxide Nanowires in Metal/SiO2/Metal Structure and Their Sensing Responses to NO2

High power silicon schottky barrier diodes with different edge termination structures