Abstract
Zinc oxide (ZnO) nanomaterials were efficiently synthesized using a microwave plasma torch system at atmospheric pressure. The Zn powder was passed through a microwave plasma region, in which it melted and vaporized. Tetrapod-type ZnO nanomaterials with a diameter of 29.8 ± 8.0 nm were synthesized using a high-purity O2/N2 mixed gas. In particular, ZnO nanowires with a diameter of 109.5 ± 8.0 nm and a length of 5–6 μm were produced using an inexpensive compressed air as a microwave plasma gas. It was confirmed that the nanowires synthesized using the compressed air showed higher light absorption in the visible region than the tetrapod-type ZnO. In addition, the redshifts in the absorption peak and photoluminescence peak were observed from 370.6 to 375.2 nm and 380 to 390 nm, respectively. The obtained results can be explained by the change of energy levels due to the defects in the ZnO nanowires such as vacancies and interstitials of Zn and oxygen. Finally, we can conclude that cost-effective compressed air is appropriate not only for the synthesis of ZnO nanowire, but also the enlargement of optical absorption and emission range.
Highlights
Zinc oxide (ZnO) has attracted much attention because it exhibits interesting physical properties as a representative wide bandgap semiconductor nanomaterial [1,2]
We confirmed from the XRD results that the Zn powder reacted in the microwave plasma to synthesize ZnO
After the microwave plasma synthesis using compressed air, high-purity air, O2, and O2/N2 mixed gas, the Zn peaks indicated by the dotted lines in Figure 2 disappeared
Summary
Zinc oxide (ZnO) has attracted much attention because it exhibits interesting physical properties as a representative wide bandgap semiconductor nanomaterial [1,2] For this reason, ZnO nanostructures are of particular interest in electronic and optical applications, such as optoelectronic devices, energy harvesting devices, sensors, and catalysts [3,4,5]. It takes a lot of energy to maintain a high temperature and a continuous process [11,12] To overcome these disadvantages, a method for synthesizing ZnO nanomaterials in a short time using a high-frequency—such as microwave or radio-frequency—power source is proposed, including an atmospheric microwave plasma torch system [13,14]. The control of morphology, as well as defects, is a very critical factor for the application of ZnO in industrial fields
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