Influence of the Gap Distance and Morphology on the Plasmon Modes of Gold Nanocube Dimers

Abstract

Plasmonic metallic nanostructures have gained significant attention due to their ability to confine light at the nanoscale. In this study, the influence of minor morphological variations by truncation of different planes on the plasmonic response of colloidal Au nanocube dimers and their separation (nanogap) is investigated by electron energy loss spectroscopy (EELS). To understand the impact of these factors, two different cube models for numerical simulations have been considered: one mimicking the truncation by {111} facets, and another mimicking their truncation by {110} ones. The experimental results, supported by numerical simulations, reveal two origins for the sensitivity of EELS spectra to nanostructure truncation: the plasmonic modes' dependence on facet geometry at the nanogap between Au nanocubes and the beam position's precision, which governs excitation efficiency. Notably, the nanogap distances between Au nanocubes are accurately measured using edge spread functions from High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, demonstrating that STEM mode provides superior precision compared to the more commonly used TEM modes. These findings contribute to a deeper understanding of the relationship between structural features and plasmonic behavior in Au nanocube dimers, crucial for the designing next-generation plasmonic devices, including quantum plasmonic systems and SERS-based sensors.