Highly sensitive mushroom-shaped gold-silica nano antenna array for refractive index sensing

In this paper, novel designs of nano antenna arrays suitable for refractive index sensing are introduced. The proposed single element design consists of a gold disk placed on top of a silica disk with the same diameter. The silica disk can be slightly radially-inward etched under the gold disk, which replicates the mushroom shape. The interaction between the analyte and the field concentration region of the gold disk is enhanced by adding the silica disk, and enhanced even more by etching this disk. This results in high sensitivity. The effects of the geometrical dimensions on the sensitivity are presented. Although the proposed structures do not possess relatively small feature dimensions, they offer sensitivity as high as 1040 nm/RIU at 1554 nm resonance wavelength.