Tailoring Plasmonics of Au@Ag Nanoparticles by Silica Encapsulation

TL;DR

This paper presents a method to synthesize Au@Ag@SiO₂ nanoparticles with tunable optical properties and demonstrates significant field enhancement due to plasmonic coupling, advancing their use in sensing and photonic applications.

Contribution

A novel synthesis approach for Au@Ag@SiO₂ nanoparticles with adjustable silica shell thickness and tunable plasmonic responses, enabling enhanced field effects.

Findings

Tunable plasmon resonance between 2.55 and 3.25 eV.

Strong coherent coupling at silver-silica interface.

Field enhancement of approximately 100% at 20 nm shell thickness.

Abstract

Hybrid metallic nanoparticles encapsulated in oxide shells are currently intensely studied for plasmonic applications in sensing, medicine, catalysis, and photovoltaics. Here, we introduce a method for the synthesis of Au@Ag@SiO$_2$ cubes with a uniform silica shell of variable and adjustable thickness in the nanometer range; and we demonstrate their excellent, highly reproducible, and tunable optical response. Varying the silica shell thickness, we could tune the excitation energies of the single nanoparticle plasmon modes in a broad spectral range between 2.55 and 3.25\,eV. Most importantly, we reveal a strong coherent coupling of the surface plasmons at the silver-silica interface with the whispering gallery resonance at the silica-vacuum interface leading to a significant field enhancement at the encapsulated nanoparticle surface in the range of 100\,\% at shell thicknesses $t\,$$\simeq\,$20\,nm. Consequently, the synthesis method and the field enhancement open pathways to a widespread use of silver nanoparticles in plasmonic applications including photonic crystals and may be transferred to other non-precious metals.