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Optical Sensitivity Gain in Silica-Coated Plasmonic Nanostructures

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posted on 17.12.2015, 04:05 by Francesco Floris, Cristiana Figus, Lucia Fornasari, Maddalena Patrini, Paola Pellacani, Gerardo Marchesini, Andrea Valsesia, Flavia Artizzu, Daniela Marongiu, Michele Saba, Andrea Mura, Giovanni Bongiovanni, Franco Marabelli, Francesco Quochi
Ultrathin films of silica realized by sol-gel synthesis and dip-coating techniques were successfully applied to predefined metal/polymer plasmonic nanostructures to spectrally tune their resonance modes and to increase their sensitivity to local refractive index changes. Plasmon resonance spectral shifts up to 100 nm with slope efficiencies of ∼8 nm/nm for increasing layer thickness were attained. In the ultrathin layer regime (<10 nm), which could be reached by suitable dilution of the silica precursors and optimization of the deposition speed, the sensitivity of the main plasmonic resonance to refractive index changes in aqueous solution could be increased by over 50% with respect to the bare plasmonic chip. Numerical simulations supported experimental data and unveiled the mechanism responsible for the optical sensitivity gain, proving an effective tool in the design of high-performance plasmonic sensors.