Comprehending nonmonochromatic plasmonic behavior of metal nanoparticles on dielectric nanowires using monochromated EELS

Combining plasmonic nanoparticles with dielectric nanostructures opens new opportunities for nanoscale control of light, yet the plasmonic field behavior in such hybrid architectures remains underexplored. Here, the authors demonstrate non-monochromatic plasmon excitations in a hybrid structure of a metal nanoparticle on a dielectric nanowire (Ag on ZnO, as a representative model). Monochromated electron energy loss spectroscopy, combined with tomography, enabled them to observe two plasmon modes with an energy difference of ~0.3 eV, whose three-dimensional near-field distributions were distinctly resolved at the nanoscale in this hybrid system. Supported by comprehensive numerical simulations, the results reveal that asymmetry in the dielectric environment surrounding the plasmonic nanoparticle governs the tunability of plasmon energies and near-field distributions.