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.

Laser pyrolysis is a synthesis method used to produce thin films and nanomaterials of high quality and purity, by intersecting a laser beam with a chemical precursor. We have chosen laser pyrolysis to synthesize tungsten trioxide starting with tungsten ethoxide precursor. The film had a thickness that varied from 205 nm to 1 µm. Xray diffraction and Raman spectroscopy confirmed the presence of a mixture of hexagonal and tetragonal phase WO 3 in the synthesized film, and it was clear that annealing greatly influenced the phases and types of structures formed. I-V curves of the films showed n-type semiconducting behaviour, but the mixed phase appeared to cause a similar behaviour of dopants in a semiconductor. The refractive index decreased with increasing wavelength and gave values of up to 21 at low wavelengths. The average optical band gap was found to 3.6 eV from UV/Vis spectroscopy. Scanning Electron Microscopy (SEM) showed a mixture of nano-and microstructures and shapes formed after annealing. One of the grown nanostructures was nanorods, this isolated using FIB for possible applications such as an active sensing medium in gas sensors.

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