Mueller Niclas S, Reich Stephanie
Department of Physics, Freie Universität Berlin, Berlin, Germany.
Front Chem. 2019 Jul 16;7:470. doi: 10.3389/fchem.2019.00470. eCollection 2019.
Theoretical modeling of surface-enhanced Raman scattering (SERS) is of central importance for unraveling the interplay of underlying processes and a predictive design of SERS substrates. In this work we model the plasmonic enhancement mechanism of SERS with perturbation theory. We consider the excitation of plasmonic modes as an integral part of the Raman process and model SERS as higher-order Raman scattering. Additional resonances appear in the Raman cross section which correspond to the excitation of plasmons at the wavelengths of the incident and the Raman-scattered light. The analytic expression for the Raman cross section can be used to explain the outcome of resonance Raman measurements on SERS analytes as we demonstrate by comparison to experimental data. We also implement the theory to calculate the optical absorption cross section of plasmonic nanoparticles. From a comparison to experimental cross sections, we show that the coupling matrix elements need to be renormalized by a factor that accounts for the depolarization by the bound electrons and interband transitions in order to obtain the correct magnitude. With model calculations we demonstrate that interference of different scattering channels is key to understand the excitation energy dependence of the SERS enhancement for enhancement factors below 10.
表面增强拉曼散射（SERS）的理论建模对于揭示潜在过程的相互作用以及SERS基底的预测性设计至关重要。在这项工作中，我们用微扰理论对SERS的等离子体增强机制进行建模。我们将等离子体模式的激发视为拉曼过程的一个组成部分，并将SERS建模为高阶拉曼散射。在拉曼截面中出现了额外的共振，它们对应于在入射光和拉曼散射光波长处的等离子体激发。正如我们通过与实验数据比较所证明的，拉曼截面的解析表达式可用于解释对SERS分析物的共振拉曼测量结果。我们还应用该理论来计算等离子体纳米颗粒的光吸收截面。通过与实验截面的比较，我们表明耦合矩阵元需要通过一个考虑束缚电子的去极化和带间跃迁的因子进行重整化，以获得正确的量级。通过模型计算，我们证明对于增强因子低于10的情况，不同散射通道的干涉是理解SERS增强的激发能量依赖性的关键。
