| Summary: | 碩士 === 國立東華大學 === 材料科學與工程學系 === 107 === Owing to its layer-dependent property, optical anisotropy, and moderate direct band gap in the visible light range, two-dimensional (2D) gallium telluride (GaTe) exhibits remarkable optoelectronic and photodetection properties and may be potentially useful for optoelectronic devices and photodetectors. With the development of 2D materials, it is anticipated that the material property can be manipulated by controlling the layer thickness of 2D materials and developing the potential applications. Here we report a simple vapor transport to synthesize GaTe nanowires and nanosheets by adjusting the growth conditions such as growth temperature, growth time, and the amount of metals used during growth. The growth condition, thickness control, and the growth mechanism of two different nanostructures were studied and discussed. In addition, the stacking of nanostructures and the growth mechanism of samples were verified by structural characterization. Their optical and visible-light-driven photocatalytic properties were examined. The results show that the two different GaTe nanostructures were both monoclinic structure with different stacking arrangements on sapphire substrate. It was found that the different morphologies were strongly affected by the growth temperature, amount of metal vapor during growth, and lattice mismatch between GaTe and substrate. For the samples grew under a lower growth temperature, a thin layer of Ga2Te3 were initially deposited on sapphire substrate due to lattice mismatch between monoclinic GaTe and hexagonal sapphire. The GaTe nanowire were subsequently grew on the surface with a [020] growth direction. However, for the samples grew under a higher growth temperature, the GaTe nanowires can be directly grown on surface due to a favorable formation Gibbs free energy. The GaTe nanowires proceed a self-assembly process to form GaTe nanosheets by the van der Waals forces between nanowires. A c-axis out-of-plane orientation were observed on both samples. The Raman spectra of samples show both samples exhibit monoclinic structure and with less vibration modes compared with those observed in the literature, which possibly due to the differences in the crystallinity and layer thickness between samples. In addition, the near-band-edge emission and defect emissions were observed in the PL spectra. The nanosheets sample shows a higher defect emission compared to nanowires sample, suggesting a high defect density exhibit in the nanosheets sample, which is in good agreement with results observed in UV/vis spectra. The visible-light-driven photocatalytic activity of samples were examined by the photodecomposition of methyl blue solution. Both nanowires and nanosheets samples show visible-light-driven photocatalytic activity, the nanosheets sample shows an insignificantly higher photocatalytic activity attributed to the higher defect density of sample.
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