Novel synthesis and controlled oxidation of indium nanoparticles and their optical properties

• Main Authors: Wu, Kun-Han, 吳坤翰
• Other Authors: Chen, Chun-Hua
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/71514647692966876601

碩士 === 國立交通大學 === 材料科學與工程學系 === 98 === This thesis contains three main topics: (i) chemical synthesis and structural analysis of five novel Indium nanostructures, (ii) oxidation dynamics of solid Indium nano-sphere and (iii) the optical properties of the prepared In nanostructures and the In-In2O3 core-shell nano-particles partial oxidized under various conditions. Firstly, we have newly synthesized five distinct indium nanostructures including solid In nano-spheres, polyhedral In nano-crystals, wormhole-like In nano-spheres, In nano-wires, and In nano-particles using a special designed chemical reduction method. The prepared solid In nano-spheres were oxidized under atmosphere at different temperatures, 100°C, 140°C, 170°C, 200°C and 250°C. The ex-situ X-ray diffraction (XRD) patterns were repeatedly recorded and the oxidation time depedent In/In2O3 ratios were then quantatively obtained for analysis of the oxidation rate law. It is found that the oxidation behaviours can be well described with Cubic law and parabolic law for oxidation temperature above and below the melting temperature of indium bulk, respectively. A distinct two-step oxidation behavior was firstly demonstrated for the nano-scaled In spheres. The extremely high internal stress caused by the inward diffusion of oxygen atoms during oxidation (N-type oxide) as well as the thermal expansion coefficient mismatches between In and In2O3 should play as an important role for the two-step oxidation. Additionally, single or multiple cracks observed in the case of greatly oxidized In nano-spheres are reasonably considered as the relaxtion of such high internal stress. However, these cracks were re-sealed at very high oxidation temperature, e.g. 400°C, due to the sintering mechanism. Optical properties including UV-Vis and PL spectra were systematically measured for the understanding of fundamentals of In and In/In2O3 core/shell nanostructures. The UV-Vis absorption spectrum shows a broaden absorption band for larger In nano-spheres (~250 nm), whereas a sharp peak around 290 nm can be found for smaller ones (~50 nm). The UV-Vis spectra of the partical oxidized In/In2O3 nano-spheres are the comprehensive absorption of the surface plasmon resonance of In metals and the optical band-gap of In2O3 semiconductors. The In2O3 thickness dependent absorption peak locates at 322 nm and 359 nm for 50 min and 20 hr oxidation time at 250°C, respectively. The PL spectra greatly vary with the oxidation conditions. For instance, a dense emission peak is typically observed around 566 nm for the case of oxidation under air, but a slight red-shifted peak over 600 nm is also frequently displayed for high pressure oxidation.