Tuning the localized surface plasmon resonance of "core-shell Ag nanoparticles on dielectric substrates" to near-infrared window: applications to surface-enhanced Raman spectroscopy

In this article, plasmonic characteristics of SiO2-Ag and hollow core Ag nanoparticles placed on dielectric substrates are investigated and tuned to the NIR wavelength spectrum for biological applications. It is shown that by placing the core-shell Ag nanoparticles on a dielectric substrate and exciting the normal plasmon mode of the nanoparticle, it is possible to obtain strong plasmon resonances at wavelengths as long as λ = 700 nm which exhibits a red shift of more than 300 nm compared to the resonance of freestanding pure Ag nanoparticles at which normal plasmon resonance wavelength shows a sensitivity of approximately 100 nm/RIU in respect to the substrate refractive index change. “SiO2-Ag and hollow core Ag nanoparticles on silicon” are optimized to exhibit a strong normal plasmon resonance at λ = 633 nm while preserving the plasmonic field enhancement intact. Finally, a three dimensional substrate for surface-enhanced Raman spectroscopy (SERS) is designed and numerically investigated. The substrate is composed of Si nanorod array decorated with the designed nanoparticles which exhibits superior characteristics such as a uniform and gapless field enhancement and an electromagnetic enhancement factor of more than 3 × 106, an order of magnitude higher than the enhancement factor for a similar structure decorated with Au nanoparticles.