【作者】 尹君；

【导师】 吴志浩； 李静；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2014， 博士

【摘要】 金属纳米结构材料,由于其特有的表面等离激元共振特性(Surface plasmon resonance, SPR),成为近些年来一个重要的研究方向。SPR特性是金属纳米结构在特定光波长照射下,表面电子随外界电磁场发生相干共振的现象,共振频率和金属纳米结构的材质、形貌和介电环境有关。SPR特性会在金属纳米结构的表面或附近形成一个局域增强的电磁场,通过调节纳米结构的尺寸和间隙可以达到103倍以上的近场增强。这种增强的光子态密度可以与半导体发光材料的激子进行耦合,增强半导体载流子的辐射复合速度,提高半导体材料的发光效率；也可以用来增强分子的拉曼散射信号,应用在表面增强拉曼散射(Surface enhanced Raman scattering, SERS)探测芯片上。由这种近场增强作用带来的远场效果(散射),也被广泛的应用于光伏转换器件的吸收增强或是LED发光器件的出光效率提高等。其中,设计和制备合适的金属纳米结构以获得对光场的有效操控,是实现以上领域应用的重要基础。然而,目前在制备合适的金属纳米颗粒阵列、实现不同波段局域场的有效调控方面仍缺乏有效的手段,尤其是在利用局域表面等离激元共振,实现紫外／深紫外区域的局域场增强、多模式的共振以及宽光谱的光场调控方面仍有待探索和研究。另外,局域表面等离激元共振(Localized surface plasmon resonance:LSPR)在增强发光和拉曼散射的内在机理方面也有待深入研究。本论文就以上表面等离激元在发光和SERS探测应用中遇到的关键问题展开研究,主要研究内容如下：首先,研究快速有效的亚波长金属纳米结构制备工艺,实现局域表面等离激元在紫外-深紫外区域的显著增强；发展高特异性金属纳米结构,实现多模式表面等离激元共振。借助于纳米球刻蚀技术、模板法、薄膜沉积技术等微纳制造工艺制备出不同材料、结构、形貌的金属纳米颗粒阵列；优化工艺参数,调控纳米颗粒的尺寸、周期性等与表面等离激元共振特性密切相关的参数；实现所制备的金属纳米颗粒LSP共振频率在近紫外、深紫外到可见光以及多模式共振的调节。通过光学表征手段结合FDTD模拟,深入研究其表面等离激元共振及光场调控特性。其次,研究局域场、LSP共振频率可调控的金属纳米颗粒在增强宽禁带半导体材料发光和SERS探测上的应用,验证金属纳米结构的优异光调控性能。采用具有不同LSP频率特性的金属纳米颗粒与近紫外、紫外宽禁带半导体发光材料或量子阱结构进行耦合,系统研究LSP共振频率与激子能量的匹配度、局域场强的分布、介质层等对于SP增强发光的影响,深入研究SP-激子的耦合机制及其对激子复合速率、复合通道的影响；引入隔离层,进一步研究电荷传输机制、耦合距离、表面态等对SP增强半导体纳米材料发光的影响。另一方面,设计金属/半导体复合纳米结构阵列,实现金属纳米颗粒间及与半导体材料的相互耦合,进一步实现对局域场分布的有效调控,以应用于SERS探测上；结合能带理论和FDTD模拟,深入研究表面增强拉曼散射的物理及化学增强机制。最后,发展和构建金属/半导体复合微腔结构,实现多模式、宽光谱的微腔耦合表面等离激元共振模式；以SERS探测和光催化辅助降解探测分子为手段,验证复合微腔阵列多模式、宽光谱的调控性能,拓展表面等离激元光调控特性在太阳能转换、可见光催化等领域的应用。更多还原

【Abstract】 Nowadays, metal nanostructures, owing to its special surface plasmon resonance (SPR) property and various potential applications, have gained much attention and been developed as an important research area. The SPR effect is well known as the coherent oscillation of the electrons near the surface of metal nanostructures when interacting with the incident light at a specific wavelength, and its resonance frequency is sensitive to the material’s type, size, shape and the exterior dielectric environment. A strong local field enhancement would be induced near the surface of the metal nanostructures when SPR phenomenahappens, and can be as high as103times on certain spots or regions. This enhanced local field, also known as the photon density of states (DOS), can be used to improve the spontaneous radiative recombination rate in semiconductor materials and thus the emission efficiency.Also, the strong local field can be applied to enhance the Raman scattering of moleculars near the surface of metal nanostructures, which is well known as the SPR based Surface Enhanced Raman Scattering (SERS) effect. On the other hand, the enhanced light scattering effect in far field due to the SPR effect has been widely used to enhance the light trapping on solar cells or light extraction on light emitting devices (LED).So, it can be concluded that the well-controlled SPR assisted light manipulation properties on the precisely designed metal nanostructures are the fundamental basis for above mentioned applications. However, up to now, in order to achieve required LSP resonance frequencies and the corresponding local field enhancements, limited fabrication methods still hinder the successful configuration of suitable metal nanostructures, especially to realize LSP resonances and local field enhancements in deep UV region, and multiple plasmonic resonances within extended broadband light region. Futhermore, the inside enhancement mechanisms of surface plasmon enhanced light emission and scattering effect still need to be investigated systematically.In this thesis, with the concern of above metioned issues existing in SPR assisted light manipulation and its practical applications like emission enhancement and SERS detecting, comprehensive fundamental investigations and reacerches have been carried out as following:Firstly, various kinds of nano-fabricating techniques have been developed to prepare size and morphology controllable metal nanostructures, and thus to realize adjustable LSPR frequencies ranging from deep UV to near-infrared region. Also, by utilizing the specific metal-semiconductor composite nanostructures, multiple plasmonic resonances have been realized and a broadband SPR based light manipulation was proposed. The nanosphere lithography (NSL) techniques, template based methods and thermal-annealing processes will be introduced to produce the metal nanostructures or metal-semiconductor nanostructures with different morphologies. RIE etching, solution heating, film thickness change and other related adjusting methods were used to control the size and distribution of the fabricated nanostructures. The LSPR properties as well as the light manipulation abilities of the prepared nanostructures also were systematically investigated by the spectroscopic characterizations and FDTD simulation.Furthermore, the as-fabricated metal nanostructures exhibiting adjustable LSPR frequencies and local field enhancements have been applied to the emission enhancements of semiconductor materials and SERS detection, and also used to verify the superior light manipulation abilities on these metal nanostructures. UV or deep UV light emission enhancements have been accomplished on ZnO or AlGaN multiple quantum well (MQW) structures decorated with LSPR-frequency-adjustable metal nanoparticles, and the corresponding mechanisms, including emission channel, enhancement ratio, defect emission suppressing, LSPR band dependence and other emission characters influenced by the SP-exciton coupling process, charge transfer process, surface modification and so on, have been systematically investigated as well. Moreover, the prepared unique metal-semiconductor nanostructures were successfully demonstrated as high sensitive SERS substrate. The physical and chemical enhancement mechanisms were further studied in more details by means of establishing the metal-semiconductor energy band model assisted and FDTD simulation.The final part of the thesis will introduce a kind of metal/semiconductor composite cavity structure with the aim to realize multiple LSP resonances showing broadband light manipulation properties. The strongly enhanced local field originated from the inter-coupling of plasmonic cavities has been verified by the high sensitive SERS detecting and the further high efficient photocatalytic reactions evidence the multiple palsmonic resonance mediated broadband light manipulation.更多还原