Enhancing Plasmon Excitation of Small Au Nanoparticles via Light Scattering from Metal-Oxide Supports

In this study, plasmonic excitation of small Au nanoparticles (NPs) deposited on metal-oxide supports (SiO2, Al2O3, SnO2, and TiO2) with particle sizes adjusted to 15 ± 1 nm was analyzed. The plasmon intensity on the support increased in the order of SiO2, Al2O3, SnO2, and TiO2, and the intensity on TiO2 was approximately 3–4 times higher than that on SiO2. Scanning transmission electron microscopy imaging revealed the formation of same-sized Au NPs on each support. In addition, Au NPs were located with sufficient spacing between them, preventing the coupling effect of multiple Au NPs. Ultraviolet–visible (UV–vis) measurements confirmed that the metal oxides with higher refractive indices scattered light more strongly. The scattering strength corresponded to the degree of plasmon enhancement induced by the support because a fraction of the light photons scattered by the support was absorbed by Au NPs. The enhancement effect of the support was more prominent for smaller Au NPs, indicating the formation of large-area contact between the Au NPs and the support material, and such a large-area contact is crucial for intensifying plasmon excitation.