基于拓扑绝缘体纳米球壳结构的紫外表面增强拉曼散射衬底研究

The substrate with high electromagnetic field enhancements is the key to realize surface enhanced Raman scattering (SERS) and its applications. At present, the SERS substrate is mainly based on Au、Ag and other noble metal nanoparticles or nanostructures. The s-d interband transitions in these commonly used metals limits its surface plasmon resonant wavelengths in the visible or near-infrared spectrum, thereby restricting the extending of SERS technology to ultraviolet region. Some topological insulators supporting plasmonic properties in the ultraviolet spectrum are recently discovered. This project is to explore and design UV-SERS substrates based on topological insulator nanostructures by utilizing the topologically protected metallic surface states with low loss and high stability. Through theoretical calculations and numerical simulations, we will investigate the coupling effects between surface states and its tunability in different nanostructures, especially in topological insulator nanoshells, for revealing the feasible approaches and physics mechanisms to obtain huge electromagnetic field enhancements, and then aims to design and prepare some UV-SERS substrates with high enhancement factor, and good stability and reproducibility based on topological insulator ordered nanostructures, and finally gives experimental verifications. This research will provide theoretical basis and novel ideas for the designs of UV-SERS activity substrates.

具有高电磁场增强的衬底是实现表面增强拉曼散射（SERS）效应和应用的关键。目前SERS衬底主要集中在Au、Ag等纳米贵金属粒子或结构，由于这些金属的s-d带间跃迁使其等离激元共振只能在可见或近红外范围，制约了SERS技术向紫外波段扩展。最近发现一些拓扑绝缘体可在紫外区产生等离激元共振。本项目提出基于拓扑绝缘体受拓扑结构保护的金属表面态的低损耗性和高稳定性，设计具有紫外电磁场增强的SERS（即UV-SERS）衬底。通过理论计算和数值模拟研究不同结构表面态的耦合效应和可调控性，重点研究纳米球壳结构的表面态耦合对紫外波段等离激元共振特性的影响，探索实现高电磁场增强的物理机制和有效途径；在此基础上设计和制备具有高增强因子、高稳定性和重现性的拓扑绝缘体有序纳米结构UV-SERS衬底，并进行实验验证。本项目研究将为UV-SERS活性衬底设计提供新的思路和理论依据。

由于常规等离子体材料（Au、Ag等金属）的带间跃迁损耗，表面等离激元共振的响应波长不能扩展到紫外区域。本项目主要研究了拓扑绝缘体纳米结构在紫外-可见波段的表面等离激元共振特性，旨在探索放大拓扑绝缘体金属表面态对集体等离子体响应贡献的有效途径，实现具有高品质因子的紫外区表面等离激元共振响应，并在此基础上开展紫外区人工电磁超表面、紫外表面增强拉曼散射衬底的设计，从而为紫外区等离激元光子学器件的实现提供理论基础。本项目的主要研究结果包括三个方面：（1）研究了拓扑绝缘体Bi1.5Sb0.5Te1.8Se1.2 (BSTS) 纳米球壳结构的表面等离激元共振特性，揭示了放大拓扑绝缘体表面态贡献的有效途径，实现了具有超高品质因子的紫外区纯Dirac型表面等离激元共振的激发（其品质因子达到52）；（2）基于拓扑绝缘体纳米椭球结构设计了工作频率在紫外波段的人工电磁超表面，实现了紫外波段的异常折射、完美透镜、涡旋光产生等功能。（3）开展具有高电磁场增强因子、且偏振不敏感等光学性能优良的表面增强拉曼散射衬底的设计。上述研究结果解决了等离激元光子学的响应波长不能扩展到紫外波段的限制，为紫外区等离激元光子学器件、紫外表面增强拉曼散射衬底的发展开辟了新的道路。