We report the 3D simulation of a disk-shaped, Moiré-type plasmonic cavity inside a photonic crystal cavity. The simulation consider normal incidence of light over the sample to be analized with a confocal microscope in reflection mode. The plasmonic cavity is made of gold, 250 nm of thickness, whose surface is modulated by a sinusoidal function. The photonic crystal cavity is made in silicon nitride film (150 nm of thickness) over a SiO2 film (500 nm) on a silicon substrate, the overall structure being Si/SiO2/SiN/Au. The simulation results show a three-fold enhancement of the electric field intensity for the plasmonic cavity within the photonic cavity, in comparison with that for the plasmonic cavity without the photonic crystal cavity. The result indicates that the electric field intensities of the photonic crystal cavity modes add to the scattered field of the plasmonic cavity, thus enhancing the electric field just above the plasmonic cavity. A preliminary test of the structure was done with a 300 nm gold film over a silicon substrate, made by focus ion beam (FIB) milling, to show fluorescence enhancement of porphiryn molecules. The structure can be elaborated to serve either as fluorescence enhancement of molecules or as Surface-enhancement Raman scattering (SERS) sensor.
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