金屬銦奈米粒子之合成、氧化控制及其光學特性之研究

Abstract

本論文架構主要分為三個部分: (i) 五大類型In奈米結構的化學合成與結構分析、(ii) 實心In奈米球體氧化動力學分析、(iii) In奈米結構及其在不同氧化條件下In-In2O3奈米核殼(core-shell)結構之光學特性。 In奈米結構化學合成部分，本研究以基本化學還原法原理為基礎，嘗試新穎製程條件與步驟，成功合成實心In奈米球體(Solid In nano-sphere)、多面體In奈米結晶(Polyhedral In nano-crystal)、蟲蝕In奈米球體(Wormhole-like In nano-sphere)、In奈米線(In nano-wire)、In奈米粒子(In nano-particle)等五種各具特色之奈米結構。 以製備所得之實心In奈米球體，進一步在大氣中，於100°C、140°C、170°C、200°C、250°C等五個溫度下進行氧化實驗，並利用非臨場X光繞射技術(XRD)，定量分析其氧化比例隨時間之變化、再藉由氧化速率方程式之探討，發現奈米In奈米球體其氧化行為視其氧化溫度在熔點之上或下而有所不同：熔點以上溫度由Cubic law描述，反之熔點以下溫度則由Parabolic law所描述。本研究發現奈米級In之氧化行為呈現二階段式氧化，亦即當氧化比例超過60%以上時，其氧化速率常數將下降1~2個數量級。此二階段氧化現象經實驗証實與高內部應力息息相關，此內部應力來自於氧化時，氧原子之向內擴散（N型氧化物特性），以及金屬In與In2O3熱膨脹係數之差異。此外，本研究亦發現隨氧化層厚度的不斷增加，導致表面應力增加誘發奈米球體破裂現象。此破裂現象隨著溫度的增加而加劇，然而當氧化溫度昇高至400°C時，反而因為高溫燒結效應，彌補了表面裂縫。 在In奈米粒子光學方面，發現UV-Vis吸收峰隨尺寸而有所不同，大尺寸(~250 nm)之In奈米粒子，其溶液顏色呈現深灰色；而小尺寸(~50 nm)之In奈米粒子，吸收峰在290 nm，其溶液顏色為褐色。而部分氧化之實心In奈米球體，其UV-Vis光譜則呈現純金屬電漿子效應與氧化物半導體能隙吸收之特性。其中In2O3層之最大吸收峰，隨氧化程度的增加而有相當明顯的紅位移現象，例如由250°C氧化50 min之322 nm，紅位移至氧化20 hr之359 nm。而PL光譜之分析中發現，其發光位置多為穩定之566 nm橘光，而發光強度隨氧化比例的增加而提昇。在高壓特殊氣氛下氧化所得之In2O3，其PL的發光強度與波長亦有別於上述正常大氣氧化之566 nm穩定橘光。

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.