Yi Jun, You En-Ming, Ding Song-Yuan, Tian Zhong-Qun
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.
Natl Sci Rev. 2020 Jul;7(7):1228-1238. doi: 10.1093/nsr/nwaa054. Epub 2020 Apr 2.
Nanostructure-based surface-enhanced infrared absorption (SEIRA) spectroscopy has attracted tremendous interest as an ultrasensitive detection tool that supplies chemical-fingerprint information. The interactions between molecular vibrations and plasmons lead to not only the enhancement of spectral intensity, but also the distortion of spectral Lorentzian lineshapes into asymmetric Fano-type or more complicated lineshapes in the SEIRA spectra; this effect hampers the correct readout of vibrational frequencies and intensities for an accurate interpretation of the measured spectra and quantitative analysis. In this work, we investigate the Fano interference between molecular vibrations and plasmons based on exact electrodynamic simulations and theoretical models. We report that, even if the molecular vibrational energy is equal to the plasmon resonant energy, the molecule-nanostructure distance-dependent dipole-dipole interactions, the plasmon-mediated coherent intermolecular interactions and the decay rates of plasmons have a significant impact on the SEIRA lineshapes. This study paves the way for controllable Fano interference at the nanoscale and more studies on plasmon-dressed molecular electronic or vibrational excited states.
基于纳米结构的表面增强红外吸收（SEIRA）光谱作为一种提供化学指纹信息的超灵敏检测工具，已引起了极大的关注。分子振动与等离激元之间的相互作用不仅导致光谱强度增强，还会使SEIRA光谱中的光谱洛伦兹线形扭曲为不对称的法诺型或更复杂的线形；这种效应阻碍了对振动频率和强度的正确读取，从而无法准确解释测量光谱和进行定量分析。在这项工作中，我们基于精确的电动力学模拟和理论模型，研究了分子振动与等离激元之间的法诺干涉。我们报告称，即使分子振动能量等于等离激元共振能量，分子 - 纳米结构距离依赖性偶极 - 偶极相互作用、等离激元介导的相干分子间相互作用以及等离激元的衰减率，都会对SEIRA线形产生重大影响。这项研究为纳米尺度上可控的法诺干涉以及对等离激元修饰的分子电子或振动激发态的更多研究铺平了道路。
