Abstract
The strong coupling between localized surface plasmons and surface plasmon polaritons in a double resonance surface enhanced Raman scattering (SERS) substrate is described by a classical coupled oscillator model. The effects of the particle density, the particle size and the SiO2 spacer thickness on the coupling strength are experimentally investigated. We demonstrate that by tuning the geometrical parameters of the double resonance substrate, we can readily control the resonance frequencies and tailor the SERS enhancement spectrum.
Highlights
Noble metal nanostructures exhibit unique optical properties due to the excitation of localized surface plasmons (LSPs) and/or surface plasmon polaritons (SPPs) [1,2,3,4,5]
For a given SiO2 thickness, the first order SPP resonance frequency is only determined by the period along the x axis
The parameters of the coupled oscillator model are fitted to the experimental data, with the results shown Fig. 2(a) as black, red and green circles
Summary
Noble metal nanostructures exhibit unique optical properties due to the excitation of localized surface plasmons (LSPs) and/or surface plasmon polaritons (SPPs) [1,2,3,4,5] These phenomena can lead to strong electromagnetic field enhancement near the nanostructure surfaces, and this has been employed for enhanced fluorescence, surface-enhanced Raman scattering (SERS), and biosensing [6,7,8,9,10,11,12,13,14,15,16,17]. It has been shown that the strong coupling between a broad radiative mode and a narrow dark mode results in a pronounced Fano line shape [20,21,22, 26,27,28,29]. EIT-like properties have been demonstrated using plasmonic nanoparticles in which the broad radiative mode is represented by the dipole plasmon mode and the narrow dark mode is represented by quadrupole plasmon mode [20,21,22]
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