Plasmonic hybridization between two metallic nanorods

Abstract

The study of the plasmonic coupling between metallic nanorods (NRs) is essential for many modern applications. In this paper, we present theoretical studies of scattering cross sections for Au-Au, Au-Ag, and Ag-Ag dimers based on the finite element method (FEM) through COMSOL Multiphysics software. Hybridization model has proposed to explain the plasmon coupling in the different dimers configurations. The single Au nanorod (Au NR) exhibits only a single plasmon resonance, which is red-shifted with increasing the NR length because intra-rod restoring forces are reduced. For asymmetric Au-Au and Au-Ag with end-to-end configuration, two peaks are appearing in the spectrum corresponding to bright (low energy) and dark (high energy) modes. The bright mode interacts strongly with the incident field compared to weak interaction of the dark mode. The bright mode is progressively blue shifted while the dark mode is slightly red-shifted as the gap between NRs increases. In the case of Ag-Ag asymmetric configuration, the two NRs are placed perpendicular to each other; the transverse and longitudinal surface plasmon modes are observed. Also, many dark plasmon hybridization coupling modes are illustrated in the range from 100 to 400 nm and ascribed to higher order plasmonic modes due to the dipole-dipole interaction. The coupling interactions between two metallic NRs can lead to significant plasmon shifts and enormous electric field enhancements. These are very useful for environmental detections, nanoantenna, Raman spectroscopy and solar cell. Also, the results of asymmetric Ag-Ag plasmonic produce new plasmon modes in the UV region that open up new opportunities for designing plasmonic devices.