Enhancing the plasmonic component of photonic-plasmonic resonances in self-assembled dielectric spheres on Ag

Photonic-plasmonic platforms consisting of dielectric sphere monolayer arrays on a plasmonic substrate have been a popular testbed for studying the hybridization of modes between dielectric and plasmonic resonances. As the plasmonic field can be used to enhance a variety of optical signals from photochemical processes, maximizing the plasmonic component is of practical interest. Herein, a modified self-assembly method at an air-liquid interface was introduced to prepare a large-scale homogeneous array of polystyrene (PS) spheres on Ag supporting photonic-plasmonic resonances in the visible range. A thin Ag coating and TiO₂film were introduced above and below the array, respectively, to tailor the spectral and spatial field characteristics such that strongly enhanced plasmonic fields could be realized. This design results in plasmonic near-field intensities that are ∼6-fold stronger than previously reported designs without the two structural additions. The simplicity and low cost of the platform provide practical routes for modulating the plasmonic contribution in hybrid resonances for optical signal-enhancing applications such as in biosensing and fluorescence spectroscopy.