Zhang Mao-Xin, You En-Ming, Zheng Peng, Ding Song-Yuan, Tian Zhong-Qun, Moskovits Martin
State Key Laboratory of Physical Chemistry of Solid Surfaces (PCOSS), Collaborative Innovation Centre of Chemistry for Energy Materials (iChEM), and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
School of Aerospace Engineering, Xiamen University, Xiamen 361005, China.
J Phys Chem Lett. 2020 Mar 5;11(5):1947-1953. doi: 10.1021/acs.jpclett.0c00304. Epub 2020 Feb 25.
Plasmonic optical antennas (POAs), often constructed from gold or silver nanostructures, can enhance the radiation efficiency of emitters coupled to POAs and are applied in surface-enhanced Raman spectroscopy (SERS) and light-emitting devices. Over the past four decades, radiation enhancement factors (REFs) of POA-emitter systems were considered to be difficult to calculate directly and have been predicted indirectly and approximately, assuming POAs are illuminated by electromagnetic plane waves without emitters. The validity of this approximation remains a significant open problem in SERS theory. Herein, we develop a method based on the rigorous optical reciprocity theorem for accurately calculating the REFs of emitters in nanoparticle-substrate nanogaps for single-molecule SERS and scanning probe-substrate nanogaps for tip-enhanced Raman spectroscopy. We show that the validity of the plane wave approximation breaks down if high-order plasmonic modes are excited. The as-developed method paves the way toward designing high-REF POA nanostructures for luminescence-related devices.
等离子体光学天线（POA）通常由金或银纳米结构构成，它可以提高与POA耦合的发射器的辐射效率，并应用于表面增强拉曼光谱（SERS）和发光器件中。在过去的四十年里，POA-发射器系统的辐射增强因子（REF）被认为难以直接计算，并且一直是在假设POA由没有发射器的电磁平面波照射的情况下进行间接和近似预测的。这种近似的有效性在SERS理论中仍然是一个重大的开放性问题。在此，我们基于严格的光学互易定理开发了一种方法，用于精确计算单分子SERS的纳米颗粒-基底纳米间隙以及针尖增强拉曼光谱的扫描探针-基底纳米间隙中发射器的REF。我们表明，如果激发高阶等离子体模式，平面波近似的有效性就会失效。所开发的方法为设计用于发光相关器件的高REF POA纳米结构铺平了道路。
