Monolayer and thin h–BN as substrates for electron spectro-microscopy analysis of plasmonic nanoparticles

The influence of four substrates [thin Si₃N₄, few-layer graphene (FLG), thin h–BN, and monolayer h–BN] on plasmon resonances of metallic nanoparticles was studied using electron energy loss spectroscopy. The h–BN monolayer is an excellent substrate for the study of plasmonic particles due to its large bandgap, negligible charging under electron irradiation, and negligible influence on the plasmon resonance full width at half maximum and peak positions. These effects were evidenced in experiments with gold nanotriangles focusing on dipolar modes. Nanotriangles on h–BN exhibit the lowest influence from the substrate compared to Si₃N₄ and FLG. In a dataset containing 23 triangles of similar sizes, the dipolar mode was found to have smaller redshifts, sharper peak widths, and higher resonance quality factors on h–BN, showing that it has nearly no effect on the plasmon absorption properties, provided that it is free from carbon contamination. However, light emission (cathodoluminescence) decreases as a function of electron irradiation for triangles on h–BN, even though the electron energy loss signal stays unchanged. This indicates the creation of non-radiative decay channels.