Boto Roberto A, Esteban Rubén, Candelas Bruno, Aizpurua Javier
Donostia International Physics Center DIPC, Paseo Manuel de Lardizabal 4, Donostia-San Sebastián 20018, Spain.
Centro de Física de Materiales CFM-MPC (CSIC-UPV/EHU), Paseo Manuel de Lardizabal 5, Donostia-San Sebastián 20018, Spain.
J Phys Chem C Nanomater Interfaces. 2024 Oct 17;128(43):18293-18304. doi: 10.1021/acs.jpcc.4c03491. eCollection 2024 Oct 31.
The enhancement of the molecular Raman signal in plasmon-assisted surface-enhanced Raman scattering (SERS) results from electromagnetic and chemical mechanisms, the latter determined to a large extent by the chemical interaction between the molecules and the hosting plasmonic nanoparticles. A precise quantification of the chemical mechanism in SERS based on quantum chemistry calculations is often challenging due to the interplay between the chemical and electromagnetic effects. Based on an atomistic description of the SERS signal, which includes the effect of strong field inhomogeneities, we introduce a comprehensive approach to evaluate the chemical enhancement in SERS, which conveniently removes the electromagnetic contribution inherent to any quantum calculation of the Raman polarization. Our approach uses density functional theory (DFT) and time-dependent DFT to compute the total SERS signal, together with the electromagnetic and chemical enhancement factors. We apply this framework to study the chemical enhancement of biphenyl-4,4'-dithiol embedded between two gold clusters. Although we find that for small clusters the total SERS enhancement is mainly determined by the chemical mechanism, our procedure enables removal of the electromagnetic contribution and isolation of the contribution of the bare chemical effect. This approach can be applied to reproduce and understand Raman line activation and strength in practical and challenging SERS configurations such as in plasmonic nano- and pico-cavities.
在等离子体辅助的表面增强拉曼散射（SERS）中，分子拉曼信号的增强源于电磁和化学机制，后者在很大程度上取决于分子与承载等离子体纳米颗粒之间的化学相互作用。由于化学和电磁效应之间的相互作用，基于量子化学计算对SERS中的化学机制进行精确量化通常具有挑战性。基于对SERS信号的原子描述，其中包括强场不均匀性的影响，我们引入了一种综合方法来评估SERS中的化学增强，该方法方便地消除了拉曼极化的任何量子计算中固有的电磁贡献。我们的方法使用密度泛函理论（DFT）和含时DFT来计算总SERS信号以及电磁和化学增强因子。我们应用此框架来研究嵌入两个金簇之间的联苯 - 4,4'-二硫醇的化学增强。虽然我们发现对于小簇，总SERS增强主要由化学机制决定，但我们的程序能够去除电磁贡献并分离出裸化学效应的贡献。这种方法可应用于在实际且具有挑战性的SERS配置（如等离子体纳米和皮秒腔）中重现和理解拉曼线的激活和强度。
