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

Abstract

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) orientedAu nanorods indicate that the transverse SPR (SPRT) has a slight red- shift, and the longitudinal SPR (SPRL) blue-shifts obviously. For the end-to-end (E-E) orientedAu nanorod dimer, the results indicate that with a decrease in the gap spacing of the E-E orientedAu nanorods, the SPRT does not shift while the SPRL 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.