Excitation and Imaging of Resonant Optical Modes of Au Triangular Nano-Antennas Using Cathodoluminescence Spectroscopy

TL;DR

This paper uses cathodoluminescence spectroscopy to analyze and visualize the resonant optical modes of gold triangular nanoantennas, revealing how substrate index and excitation methods influence plasmonic behavior.

Contribution

It introduces a high-resolution CL spectroscopy approach combined with specific nanoantenna designs to better understand and excite various plasmonic modes, validated by simulations.

Findings

Efficient excitation of antenna modes using low index substrates.

High-contrast tip illumination of out-of-plane dipole modes.

Excellent agreement between experimental results and simulations.

Abstract

Cathodoluminescence (CL) imaging spectroscopy is an important technique to understand resonant behavior of optical nanoantennas. We report high-resolution CL spectroscopy of triangular gold nanoantennas designed with near-vacuum effective index and very small metal-substrate interface. This design helped in addressing issues related to background luminescence and shifting of dipole modes beyond visible spectrum. Spatial and spectral investigations of various plasmonic modes are reported. Out-of-plane dipole modes excited with vertically illuminated electron beam showed high-contrast tip illumination in panchromatic imaging. By tilting the nanostructures during fabrication, in-plane dipole modes of antennas were excited. Finite-difference time-domain simulations for electron and optical excitations of different modes showed excellent agreement with experimental results. Our approach of efficiently exciting antenna modes by using low index substrates is confirmed both with experiments and numerical simulations. This should provide further insights into better understanding of optical antennas for various applications.