基于微纳结构半导体材料Mie共振调控的SERS增强机制研究

An increasing interest in the studies of surface-enhanced Raman scattering (SERS) in semiconducting materials has emerged owing to its potential application in biological and photoelectronic analyses. It should be pointed out that a full understanding of the enhancement mechanism has been a priority issue for promoting the development of semiconductor-based SERS technique. The photo-induced charge-transfer model has been well established, which help us find lots of SERS-active semiconductor substrates, thus most previous research consider that the chemical enhancement mechanism plays a key role in semicondutor-based SERS. However, it is difficult to clearly explain the experimental phenomenon in the absence of electromagnetic mechanism, especially for the huge enchantment in same semiconductor materials. In fact, on the basis of the Mie theory, Mie resonance stemmed from submicrometer semiconductor structure could increase the local electric field, and thus increasing the efficiency of near-field enhancement at the submicrometer structure surface. This study will focus on investigating electromagnetic mechanism of SERS in submicrometer semiconductor sphere based on Mie theory. The motivation of this study is to investigate the basic theory of electromagnetic mechanism in semiconductor-based SERS. Here, the position of Mie resonance will be turned through changing the size and refractive ration of semiconductor materials. Meanwhile, the field distribution and strength at the surface of submicrometer semiconductor sphere will be calculated by the finite-difference time-domain method. This study will provide a preliminary electromagnetic enhancement model for SERS in semiconductors, and also open up a simple and effective rout to construct SERS-active semiconductor substrate with high sensitivity.

基于半导体的表面增强拉曼散射（SERS）研究对SERS技术应用领域的拓宽具有极为重要的意义，其中增强机制的建立是半导体SERS技术发展中亟待解决的关键问题。光诱导电荷转移模型的提出促使研究者在更多的半导体材料表面观测到SERS效应，但基于该模型的化学增强机制并不能完全解释实验中观测到的现象，电磁场增强模型的缺失使得半导体SERS备受质疑。理论研究表明半导体微纳结构可以产生强烈的Mie共振效应，提升局域电场强度，从而提高近场散射效率。本项目拟以微纳结构半导体材料作为SERS活性基底，通过改变半导体的尺寸和折射率调控基底Mie共振模式的场分布，研究Mie共振对半导体SERS效应的影响，并结合理论计算深入揭示Mie共振与半导体SERS电磁场增强机制的内在关联，初步构建半导体SERS的物理增强模型，提高对半导体SERS增强机制的认识，同时为设计和改善半导体SERS活性基底及其灵敏度提供新思路。

半导体微纳结构可以产生Mie共振效应，提升局域电场强度，从而提高近场散射效率。本项目以亚微米球形半导体粒子为模型，开展基于半导体Mie共振调控的SERS增强机制研究。主要目标集中在：1）开发可用于球形半导体粒子近场散射效率计算的程序代码，为研究和设计具有Mie共振效应的微纳结构半导体材料提供理论指导；2）依据理论计算结果，制备可产生Mie共振效应的亚微米级球形半导体粒子，研究Mie共振特性与SERS效应的内在关联，探讨Mie共振效应对SERS增强的作用规律，构建基于Mie共振效应的半导体SERS电磁场增强机制；3）依据构建的增强机制模型，设计并制备几种新型SERS活性半导体基底材料，验证增强机制的合理性。.基于Mie近场散射理论，开发了可用于球形半导体粒子近场散射效率计算的程序代码，系统研究了半导体材料折射率、粒径及激发光波长对Mie共振效应的作用规律。理论研究表明，具有高折射率，低介电常数的半导体材料可以产生较强的Mie共振模，是制备高SERS活性半导体基底的理想材料。以亚微米级ZnO超结构作为模型，理论和实验研究发现Mie共振效应可以对SERS增强产生电磁场增强贡献，其大小近似等于近场散射效率的平方。同时，Mie共振效应可以与化学增强贡献耦合，产生协同增强贡献，显著提高半导体材料的SERS活性。在构建的理论框架下，设计和制备了亚微米级球形ZnO超结构和亚微米级中空V2O5粒子，在这两种基底表面均获得了较高的SERS增强效果，归因于Mie共振和化学增强机制协同作用的结果。这些实验结果进一步证实我们基于Mie共振效应构筑的半导体SERS电磁场模型具有正确性和普适性。.半导体SERS电磁场增强模型的构建，拓展了半导体SERS技术的普适性，在应用时不必受限于分析物的能级结构。这一理论和实验上的突破为我们对涉及半导体材料表/界面问题的全面深入研究提供了契机。同时，也将为半导体SERS活性基底的设计与合成提供新策略，对半导体SERS技术的改进和推广有着极为重要的指导意义。