We engineer very low aspect ratio Aluminum (Al) based periodic plasmonic nanostructures with period ≈ resonance wavelength for enhanced refractive index and thickness sensing, which offer to access complete ultraviolet-visible-near infrared spectral range for SPR sensors. Al-based periodic nanostructures on top of a thin homogeneous Al metal coated on a BK-7 glass substrate were designed by systematic variation of geometrical parameters using Rigorous Coupled Wave Analysis and finite elements full wave solver, while, taking into account applicable fabrication constraints. The reason of adding a thin layer of homogeneous Al metal between the nanostructure and glass substrate was to convert the signature of Surface Plasmons (SPs) from transmission dips to transmission peaks, using ±1st order diffraction mode. The shift in SP mode excited on the nanostructure-analyte interface was used to measure the variation in refractive index, and the number of waveguide modes with the increase in the thickness of the analyte was used to capture the variation in thickness of the analyte. The proposed nanostructures of period 400 nm and an aspect ratio of 0.1 offered a sensitivity of 400 nm/RIU and full width at half maximum of 18 nm resulting in a figure of merit of 22. These plasmonic nanostructures have potential to be used as refractive index and thickness sensor due to a high figure of merit, high localization of the field, and very low aspect ratio that is needed to maintain laminar flow of analyte.
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