| Summary: | 碩士 === 國立臺北科技大學 === 機電整合研究所 === 95 === In the present study, tungsten oxide nanomaterials were synthesized by a modified plasma arc gas condensation technique. The effects of the plasma currents (70~90 A) and chamber pressures (200~600 Torr) on the preparation of tungsten oxide nanostructures were investigated. The optical, filed emission, and gas sensing properties of tungsten oxide nanorods were also examined. The morphology of tungsten oxide nanomaterials was equiaxed and turn into rod-like nanoparticles with increasing plasma currents or chamber pressures. Generally, the relative amount, diameter, and length of tungsten oxide nanorods increased with increasing plasma currents or chamber pressures. The aspect ratio of the as-prepared tungsten oxide nanorods reached a maximum of 12.7 with a plasma current of 90 A and a chamber pressure of 400 Torr. X-ray diffraction results showed that all the nanomaterials investigated in the present study were W5O14 phse. High resolution transmission electron microscopy observation revealed that tungsten oxide nanorods grown along the [001] direction with a lattice spacing of 0.38 nm and the Vapor-Solid (VS) process is responsible for the growth mechanism. The W5O14 nanorods growth results in the distorted crystalline structure and adding d-state electrons number of tungsten atoms.
Photolumeinscence emission at ultraviolet-visible (365 nm) and blue (444 nm) regions are found in the W5O14 nanorods, which is caused by band-band transition and oxygen vacancies, respectively. And the band gap of tungsten oxide nanorods is 3.4 eV. The turn-on field of W5O14 nanorods is 1.7V/µm and the current density is decreasing with the increasing vacuum gap. However, the thermal stability of W5O14 nanorods is good enough under the test environment of 300℃ and 48 hours. The sensitivity for NO2 gas with 1~4ppm is excellent under 200℃ and proportional to the NO2 gas concentration.
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