Abstract
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 SiO2 dielectric layer thicknesses. SiO2 layers both beneath and over the Ag NPs affected the resonance wavelengths of local surface plasmons (LSPs). By adjusting the SiO2 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 SiO2 before NPs fabrication and then overcoating the NPs with various SiO2 thicknesses from 5 nm to 20 nm, the dipole surface plasmon resonances changed from 450 nm to 490 nm. The SiO2 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 SiO2 cladding layer because the dielectric SiO2 can suppress level splitting of surface plasmon resonances caused by the Ag NP coupling effect.
Highlights
Surface plasmons are attracting increasing interest because of their localised surface plasmon resonance (LSPR) properties, which induce large local electromagnetic field enhancements and can be used to improve the performance of optoelectronic devices[1,2,3,4,5]
Especially those in the near violet and visible region, Ag nanoparticles are considered to be better than other metallic materials because they exhibit reduced parasitic absorption, which comprises unwanted losses that arise from resonant coupling of the incident sunlight to the nanoparticles[12,13]
The results showed that the dipole surface plasmon resonances of the local surface plasmons (LSPs) can be shifted and stably between 410 nm and 490 nm by adjusting the thickness of the SiO2 beneath and overcoating the Ag NPs
Summary
Surface plasmons are attracting increasing interest because of their localised surface plasmon resonance (LSPR) properties, which induce large local electromagnetic field enhancements and can be used to improve the performance of optoelectronic devices[1,2,3,4,5]. When the energy of the incident or emitted light coincides with the localised surface plasmon energy, an effective energy transfer occurs from the light beam to the local surface plasmons (LSPs). The degree of peak energy matching between the resonance energy of the LSPs and the energy of the light determines the localised surface plasmon enhancement factor. The closer that these two energies are, the more that the resulting performances of the optoelectronic devices will be enhanced. The results showed that the dipole surface plasmon resonances of the LSPs can be shifted and stably between 410 nm and 490 nm by adjusting the thickness of the SiO2 beneath and overcoating the Ag NPs. The time-domain and frequency-domain finite-element methods were used to explain the tunable mechanism. The results presented here represent a further step towards greater efficiency enhancement for GaN-based LEDs
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