Tunable Dipole Surface Plasmon Resonances of Silver Nanoparticles by Cladding Dielectric Layers

The tunability of surface plasmon resonance can enable the highest degree of localised surface plasmon enhancement to be achieved, based on the emitting or absorbing wavelength. In this article, tunable dipole surface plasmon resonances of Ag nanoparticles (NPs) are realized by modification of the SiO(2) dielectric layer thicknesses. SiO(2) layers both beneath and over the Ag NPs affected the resonance wavelengths of local surface plasmons (LSPs). By adjusting the SiO(2) thickness beneath the Ag NPs from 5 nm to 20 nm, the dipole surface plasmon resonances shifted from 470 nm to 410 nm. Meanwhile, after sandwiching the Ag NPs by growing SiO(2) before NPs fabrication and then overcoating the NPs with various SiO(2) thicknesses from 5 nm to 20 nm, the dipole surface plasmon resonances changed from 450 nm to 490 nm. The SiO(2) cladding dielectric layer can tune the Ag NP surface charge, leading to a change in the effective permittivity of the surrounding medium, and thus to a blueshift or redshift of the resonance wavelength. Also, the quadrupole plasmon resonances were suppressed by the SiO(2) cladding layer because the dielectric SiO(2) can suppress level splitting of surface plasmon resonances caused by the Ag NP coupling effect.