Tailoring Plasmonics of Au@Ag Nanoparticles by Silica Encapsulation

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