Mode Mixing and Substrate Induced Effect on the Plasmonic Properties of an Isolated Decahedral Gold Nanoparticle

Abstract

We report new results on the localized surface plasmon (LSP) assisted optical effects of a single noble metal nanoparticle (MNP) in nm level spectral and spatial domain which is related to the phase retardation of electromagnetic signal with larger particle size. Site selective electron beam excitation in a scanning electron microscope (SEM) show multiple resonance peaks in the cathodoluminescence (CL) spectra of an isolated gold decahedron of side edge length 230 nm sitting on a silicon (Si) substrate. Apart from a substrate induced LSP mode in the near-infrared (750 nm) region, finite-difference time-domain (FDTD) numerical analysis also identifies two prominent LSP modes in the visible region. While the shorter wavelength (560 nm) mode has a mixture of in-plane quadrupolar and out-of-plane quadrupolar charge distribution pattern, the longer wavelength (655 nm) mode has the dipolar charge pattern in both the direction. We also analyze numerically to show the critical size of the side edge length of the decahedron particle where mode mixing is initiated