Qin Kang, Liu Kai, Peng Sheng, Zuo Zongyan, He Xiao, Ding Jianping, Lu Yanqing, Zhu Yongyuan, Zhang Xuejin
National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, Key Laboratory of Intelligent Optical Sensing and Manipulation, Jiangsu Key Laboratory of Artificial Functional Materials, College of Engineering and Applied Sciences, Nanjing University, No. 22, Hankou Road, 210093 Nanjing, P.R. China.
National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, No. 22, Hankou Road, 210093 Nanjing, P.R. China.
Nanophotonics. 2023 Mar 30;12(10):1857-1864. doi: 10.1515/nanoph-2023-0016. eCollection 2023 May.
Recent advances in near-field technology with an ultrahigh spatial resolution breaking optical diffraction limit, make it possible to further identify surface-enhanced Raman scattering (SERS) enhancement theories, and to monitor the SERS substrates. Here we verify the electromagnetic enhancement mechanism for SERS with a close-up view, using scattering-type scanning near-field optical microscopy. The array of metal-insulator-metal (MIM) subwavelength structures is studied, in which the field enhancement comes from the strong coupling between gap plasmon polariton and surface plasmon polariton modes. The near-field optical measurements reveal that SERS enhancement factor (EF) varies from one MIM subwavelength unit to another in a finite array. Besides the enhancement of isolated unit, the loss exchange phenomenon in strong coupling with a large Rabi splitting can give rise to an additional enhancement of more than 2 orders of magnitude in periodic arrays and close to 3 orders of magnitude in finite arrays. The SERS EF of the array composed of only 5 units is demonstrated to yield the best SERS performance. Our near-field optical measurements show evidence that finite-size structures embodied with strong coupling effect are a key way to develop practical high-performance SERS substrates.
近场技术的最新进展实现了超高空间分辨率，突破了光学衍射极限，使得进一步确定表面增强拉曼散射（SERS）增强理论以及监测SERS基底成为可能。在此，我们使用散射型扫描近场光学显微镜，近距离验证了SERS的电磁增强机制。我们研究了金属-绝缘体-金属（MIM）亚波长结构阵列，其中场增强源于间隙等离激元极化激元和表面等离激元极化激元模式之间的强耦合。近场光学测量表明，在有限阵列中，SERS增强因子（EF）在不同的MIM亚波长单元之间变化。除了孤立单元的增强外，具有大拉比分裂的强耦合中的损耗交换现象可在周期性阵列中产生超过2个数量级的额外增强，在有限阵列中接近3个数量级。由仅5个单元组成的阵列的SERS EF被证明具有最佳的SERS性能。我们的近场光学测量表明，具有强耦合效应的有限尺寸结构是开发实用高性能SERS基底的关键途径。
