Insight on the Coupling of Plasmonic Nanoparticles from Near-Field Spectra Determined via Discrete Dipole Approximations.
Insight on the Coupling of Plasmonic Nanoparticles from Near-Field Spectra Determined via Discrete Dipole Approximations.
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DOI：
10.1021/acs.jpcc.1c01071
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发表时间：
2021-03-11
期刊：
影响因子：
--
通讯作者：
Wang Y
中科院分区：
文献类型：
--
作者：
Barr JW;Gomrok S;Chaffin E;Huang X;Wang Y
纳米颗粒组件中的等离子体纳米颗粒（NP）之间的耦合已通过远场特性（例如吸收和散射）进行了广泛研究，但很少通过近场特性进行研究，对近场特性的定量研究应该可以深入了解耦合的本质。我们报告了一种利用离散偶极近似 (DDA) 获得球形金纳米粒子 (Au NP) 周围可靠的近场光谱 (QNF) 的数值程序。通过比较 DDA 计算的 QNF 与 Mie 理论的精确结果来测试该方法的可靠性。然后，我们应用该方法来检查以线性排列方式组装的二聚体、三聚体和五聚体的金纳米颗粒。对于经过充分研究的二聚体系统，我们发现由于纵向模式耦合而产生的 QNF 增强远大于 Qext 的增强。 QNF 和 Qext 峰位置之间存在线性相关性，QNF 峰相对于 Qext 峰红移平均约 12 nm。对于多聚体，各个球体的 QNF 光谱并不总是相同，并且取决于球体位置。在纵向模型中，中心球体具有最强的 QNF 谱。对于横向模式，我们区分两种不同的情况，横向-Y，其中电场（E）和光传播矢量（k）都垂直于链轴，横向-X，其中k平行于链轴。在横向 Y 模式中，耦合导致 QNF 光谱减少，并且中心球体具有最低的 QNF 强度。在横向X模式下，从前球面到后球面存在延迟效应。来自前球体的 QNF 比来自后球体的 QNF 更强。此外，由于 k 方向上的相位滞后，对于大颗粒，横向 X 方向的 QNF 与横向 Y 方向的 QNF 可能存在显着差异。当人们考虑相邻纳米粒子上的感应偶极子产生的电场如何增加或减少入射电场时，所有这些结果都可以理解。这些结果为金纳米粒子的耦合特性提供了新的见解。
Coupling between plasmonic nanoparticles (NPs) in nanoparticle assemblies has been investigated extensively via far-field properties, such as absorption and scattering, but very rarely via near-field properties, and a quantitative investigation of near-field properties should provide great insight into the nature of the coupling. We report a numerical procedure to obtain reliable near-field spectra (QNF) around spherical gold nanoparticles (Au NPs) using Discrete Dipole Approximation (DDA). The reliability of the method was tested by comparing QNF from DDA calculations with exact results from the Mie theory. We then applied the method to examine Au NPs assembled in dimer, trimer, and up to pentamer in a linear arrangement. For the well-studied dimer system, we show that the QNF enhancement, due to coupling in longitudinal mode, is much greater than the enhancement in Qext. There is a linear correlation between the QNF and Qext peak positions, with the QNF peak redshifted from the Qext peak by an average of approximately 12 nm. In the case of the multimers, QNF spectra from individual spheres were not always identical and become dependent on the sphere location. In the longitudinal model, the center sphere has the strongest QNF spectra. For the transverse mode, we differentiate two different scenario, transverse-Y where both electric field (E) and light propagation vector (k) are perpendicular the chain axis, and transverse-X where k is parallel to the chain axis. In transverse-Y mode, coupling leads to reduced QNF spectra and the center sphere has the lowest QNF intensity. In transverse-X mode, there is retardation effect from the front sphere to the back sphere. The QNF from the front sphere is stronger than from the back sphere. In addition, due to the phase lag in k-direction, the QNF in transverse-X can differ quite significantly from transverse-Y for large particles. All these results could be understood when one considers how electric field from induced dipoles on neighboring NPs add on or subtract from the incident E-field. These results provide new insight into the coupling properties of Au NPs.
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