【作者】 何金娜；

【导师】 梁二军；

【作者基本信息】 郑州大学 ， 光学， 2011， 硕士

【摘要】 电磁波与金属纳米材料相互作用时表现出体相金属材料(bulk metal)所不具备的光学性能,引发一系列新效应和新现象,例如表面等离子体(Surface Plasmons)和能实现自然媒质所不具备的新型电磁特性的电磁超介质(Meta-materials)。随着纳米制造技术方面的发展,人们基本上能实现具有任意形状或结构的金属纳米材料的制备,因此也加速了这些新兴学科或领域的发展。传统的表面增强拉曼光谱(Surface Enhanced Raman spectroscopy, SERS)基底的拉曼信号的重现性和稳定性较差,严重制约了表面光谱技术的广泛应用。因此基于金属纳米材料的表面等离子体性能,人为设计结构单元实现高电磁场增强,高稳定性和重现性的SERS基底目前已被广泛研究。本文主要是设计一种金纳米环-SiO2-金膜的周期性阵列结构,并研究了在表面等离子体模式耦合下的双带共振性能及相应的电场分布。该结构双带的高SERS增强因子在表面光谱技术方面具有潜在的应用价值。本文一共分为五个部分。绪论部分主要介绍了SERS的发展由来及研究现状,并在此基础上提出了本论文的工作设想和主要内容。第二部分主要介绍金属纳米材料的表面等离子体性能以及局域场增强效应。第三部分则主要介绍了离散偶极子近似(Discrete dipole approximation, DDA)的理论基础,并分析了其模拟计算金属纳米材料电磁性能的有效性。第四部分则借助DDSCAT7.0的仿真工具,具体讨论了金纳米环-SiO2-金膜结构的光学性能。首先,与没有金膜相比,由于金纳米环与其在金膜中感应的镜像电荷之间的相互作用,该结构有着更高的局域场强增强因子,并且带来了近乎完美的吸收。其次,金纳米环周期性阵列作为光栅能耦合垂直入射光激发出表面等离子体激元(Surface Plasmon Polaritons, SPP)。通过改变周期调节SPP与LSPR发生强烈耦合,在强烈耦合条件下,该结构表现出双带共振和进一步的局域电场增强,SERS增强因子可以分别达到1.5×10和1.4×106。第五章为全文总结与展望。本论文工作的创新点及主要成果有以下三个方面：1.以往的SERs基底往往局限于单个的金属纳米颗粒以及单带的局域电场增强。本论文提出的金纳米环-SiO2-金膜的周期性阵列结构实现了双带的局域电场增强。另外,98%的吸收系数为目前的完美吸收体以及薄膜太阳能电池方面的研究提供了参考价值。2.目前,离散偶极子近似方法主要用于研究单个金属纳米颗粒的光学性能,对周期性的金属纳米结构的研究还比较少。本论文则通过与一些已经公开发表的有实验数据的文献的结果相比较,分析了用离散偶极子近似方法研究周期性金属纳米结构电磁性能的有效性。3.从理论上系统的分析了金属纳米材料的表面等离子体模式以及相应的局域场增强效应,并指出等离子体模式之间的耦合效应是提高SERS增强因子的关键因素。更多还原

【Abstract】 The interaction between electromagnetic waves and metallic nanostructures brings optical properties which are unavailable for bulk metal materials, results in a series of new phenomena or effects, for example Surface Plasmons and "Meta-materials" which can realize some interesting electromagnetic properties not found in naturally occurring materials. With the development of manufacturing technology on the nanoscale, people can almost fabricate nano-scale metal structures with arbitrary geometries and accelerate the development of these new subjects and fields, The poor reproducibility and stability of Raman signals for traditional SERS substrates prevents the application of surface optical spectral technology seriously. Considering the lack of control in traditional SERS produced by chemical process, we proposed a kind of periodic structures based on the properties of surface plasmons. Dual-band resonance, large SERS enhancement factor and good reproducibility and stability make the structure attractive as SERS substrate.The thesis is divided into five parts. The introduction mainly presents the origin and actuality of SERS, and the idea and main tasks of this work. In chapter two, we mainly introduce the surface plasmon properties of metallic nanostructure and the corresponding localized field enhancement effects. In chapter three, after a brief introduction to basic electromagnetic theory, particular attention is devoted to the numerical method of discrete dipole approximation (DDA) and its credibility to deal with the interaction of light with periodic metallic nanostructures. In chapter four, the optical properties of the proposed structure are investigated using the discrete dipole approximation (DDA) method. Due to coupling between the particles and the gold film, the proposed structure exhibits higher absorption and larger field enhancement compared to the nanoring array alone. In addition, periodic nanorings as grating couples to surface plasmon polaritons (SPP). The plasmonic coupling between localized surface plasmon resonance (LSPR) of the nanorings and SPP can enhance the electric field around gold rings further and gives rise to dual-band resonance absorptions. The corresponding Raman signal enhancement factors can reach 1.5×107 and 1.4×106, respectively. The fifth section is in summary and prospect.The main progresses and innovation of this work are listed as follows:1. A large proportional of nanoparticles as SERS substrates can realize single band resonance for field enhancement. The proposed structure is attractive for applications as double-resonance plasmon substrates due to the coupling between LSPR and SPP. In addition, the absorption coefficient of 97.97% is potentially helpful for perfect absorber and thin solar cells in near-infrared spectrum.2. DDA method’credibility to deal with the interaction of light with periodic metallic nanostructures is proved by calculate the optical properties of periodic nanostructures in reference which is in accordance with the experimental results.3. We investigate the localized field enhancement effects of metallic nanostructures systematically. The coupling effects between surface plasmons modes are key point for improving the SERS enhancement factor.更多还原