金纳米棒组装体表面等离子体共振耦合效应的FDTD模拟

贵金属纳米结构的光学性质与其尺寸、形貌、介质环境等因素的相关性是基础研究领域的重要内容. 本文利用时域有限差分（FDTD）方法，计算了不同构型二聚体和多聚体的表面等离子体共振（SPR）特性. 研究了金纳米棒结构和组装方式对SPR耦合效应的影响，模拟结果与实验规律比较吻合. 金纳米棒二聚体的光吸收结果表明：对于肩并肩（S-S）的组装体，随着间隙的减小，金纳米棒的横向SPR（SPR_T）峰有较小的红移，而纵向SPR（SPR_L）峰显著蓝移. 对于端对端（E-E）的组装体，随着组装体间隙的减小，金纳米棒的SPR_T峰无明显移动，而SPR_L峰显著红移，并在近红外较长波段范围内出现新的共振峰，其强度随着间隙的减小而增强；结合弹簧振子模型和纳米颗粒在外电场作用下的极化，对组装体共振吸收峰的移动和新的耦合共振峰的出现提出了初步的解释.

Surface Plasmon Resonance Coupling Effect of Assembled Gold Nanorods Based on the FDTD Simulation

Much attention has been given to the optical properties of noble metal nanostructures and these are closely related to the size, morphology, and environment of the nanoparticles. In this paper, the influences of structures and assembly modes on the surface plasmon resonance (SPR) of Au nanorods were studied through a finite-difference time-domain (FDTD) simulation on Au nanorod assemblies (dimers and multimers) of different configurations. The simulated optical spectra agree well with the experimental results. The simulated results for the side-by-side (S-S) oriented Au nanorods indicate that the transverse SPR (SPR_T) has a slight redshift, and the longitudinal SPR (SPR_L) blue-shifts obviously. For the end-to-end (E-E) oriented Au nanorod dimer, the results indicate that with a decrease in the gap spacing of the E-E oriented Au nanorods, the SPR_T does not shift while the SPR_L red-shifts obviously. Moreover, a new coupling SPR peak appears in the near-infrared (NIR) region, blue-shifting and enhancing with a decrease in the gap spacing. Based on the spring oscillator model and the polarization of the nanoparticles under an incident electric field, we propose a reason for the SPR shift and the appearance of a new coupling SPR for the Au nanorod assemblies.