Electron energy loss spectroscopic investigation of Mie resonances in bimetallic nanostructures

Abstract

Bimetallic nanostructures can exhibit significant broadening of Mie resonances compared to monometallic nanoparticles. Here, we study these materials using Electron Energy Loss Spectroscopy at a single particle level. This technique is immensely effective to probe direct structure-property correlation of nanoparticles. We are thus able to confirm the broadening of Mie resonances at a single particle level. This effect is analyzed in the context of emergence of a new dielectric constant that originates from metallic interfaces. We employ Coronado-Schatz corrections to the usual dielectric constants of the constituent metals to quantitatively simulate these materials. The resultant materials thus exhibit optical cross-sections that are 38.5 % and 4.2 % of the gold and silver nanoparticle optical cross-section at 2.5 eV and 3.45 eV, respectively. A strong agreement between theory and experiment is observed. We also confirmed the effectiveness of our approach for nanoparticles with different morphologies as well as different compositional ratios. Our study suggests an effective strategy to regulate the dielectric properties of bimetallic nanostructures through interface engineering.