Catalyst-Free Synthesis of Single-Crystalline WO3-x Nanowires via Thermal Evaporation and Their Physical Properties

• Main Authors: Chao-WeiTing, 丁照緯
• Other Authors: Kuo-Chang Lu
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/n6mmes

碩士 === 國立成功大學 === 材料科學及工程學系 === 106 === In our study, oxygen-vacancy-rich tungsten oxide nanowires were synthesized on Si via grain-by-grain thermal evaporation method without any catalyst; also, WO3-x nanowires were grown on W foil as comparison on their physical properties and growth mechanism. In the SEM cross-section images, we have clearly found that there is no thin film formation in the growth mechanism of tungsten oxide grown on Si. It shows that this process is a new grain-by-grain thermal evaporation method which nanowires grown from the previously deposited tiny nanoparticles. Surprisingly, the oxygen-vacancy-rich tungsten oxide nanowires grown on Si were found to have unusual W5+ dominated energy bond and the ratio of tungsten to oxygen was about 5:13 based on XPS analysis. TEM studies show that the lattice arrays of oxygen-vacancy-rich tungsten oxide nanowires grown on Si were crystalline, while those of WO3-x nanowires grown on W foil were improved in terms of crystallization with increase of growth temperature. We demonstrated this result with XRD analysis as well. For physical property measurements, the oxygen-vacancy-rich nanowire grown on Si had a very low resistivity of 7.03 x 10-4 Ω ‧ cm, while the resistivity of WO3-x nanowires grown on W decreased as the growth temperature rises. Additionally, we found that WO3-x nanowires exhibit different magnetic properties depending on the valence state of tungsten. Notably, the oxygen-vacancy-rich tungsten oxide nanowires grown on Si possessed special antiferromagnetic properties. For visible light photocatalytic applications, the WO3-x nanowires grown on W at the lowest temperature have the best degradation efficiency to methylene blue solution.