A New Proposal for Highly Sensitive Refractive Index Sensor Using Vertically Coupled Plasmonic Elliptic-Disk up Elliptic-Ring Nanoparticles

Abstract

In this research work, a novel highly sensitive refractive index sensor using Au and Ag elliptic-shaped nanoparticles are proposed. The main idea of this work is using an original elliptic-disk nanoparticle that, in constant volume, is decomposed into two particles as a form of smaller elliptic-disk up elliptic-ring to improve the sensitivity. The better optical sensing properties of the proposed nanostructure are the main factor before considering their details. The optimum arrangement is found to have strong vertical coupling, and hence a high sensitivity. A plasmonic resonance peak takes place for the new nanostructure. The sensitivity of 320 nm/RIU and full width at half maximum (FWHM) of 66.5 nm is obtained for Au elliptic-disk nanoparticles. It is important to mention that these values are 260 nm/RIU and 57.3 nm for Au circular-disk nanoparticles, respectively. By decomposing the Au elliptic-disk as a form of elliptic-disk up elliptic-ring, the sensitivity is increased to higher than 440 nm/RIU. Also, the FWHM of the detector is 55.3 nm, and its figure of merit (sensitivity/FWHM) is 7.95. A nanostructure of Ag shows a sensitivity of 416.6 nm/RIU. Its FWHM and FOM are 51.1 nm and 8.15, respectively. The arrangement of decomposed nanoparticles causes the field to be remarkably enhanced at their point of coupling.