Several different synthetic methods have been developed to fabricate tungsten oxide (WO_3) nanostructures, but most of them require exotic reagents or are unsuitable for mass production. In this paper, we present a systematic investigation demonstrating that arc discharge is a fast and inexpensive synthesis method which can be used to produce high quality tungsten oxide nanostructures for NO_2 gas sensing measurements. The as-synthesized WO_3 nanostructures are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), finger-print Raman spectroscopy and proton induced x-ray emission (PIXE). The analysis shows that spheroidal-shaped monoclinic WO _3 crystal nanostructures were produced with an average diameter of 30nm (range 10-100nm) at an arc discharge current of 110A and 300Torr oxygen partial pressure. It is found that the morphology is controlled by the arc discharge parameters of current and oxygen partial pressure, e.g.a high arc discharge current combined with a low oxygen partial pressure results in small WO_3 nanostructures with improved conductivity. Sensors produced from the WO_3 nanostructures show a strong response to NO_2 gas at 325 °C. The ability to tune the morphology of the WO_3 nanostructures makes this method ideal for the fabrication of gas sensing materials.
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