Plasmonic enhanced gas sensing using polarization-insensitive 3D hybrid nanostructures

Abstract

This paper investigates a hybrid coupled plasmonic gas sensor with stacked gold-SiO2 layers for air-quality monitoring. The gas absorption characteristics of hybrid-stacked layers sensors are studied and compared with single-layer sensors. Gases with different refractive indexes changing from 1 to 1.4 are studied. The total absorption radar cross section (ACS) has increased from 1.681 × 105 nm2 for single-layer sensors to 5.021 × 105 nm2 for hybrid stacked layers sensors. A graphene monolayer is used to enhance the total gas absorption. It acts as an insulator to the dipole sensor. The lumped-element equivalent circuit is developed using a particle swarm optimization technique (PSO). The sensitivity is 788 nm/RIU for the single-layer sensor and 910 nm/RIU for the hybrid-stacked layers sensor with a graphene monolayer placed as a cover for the plasmonic dipole. A polarization-insensitive sensor concerning the direction of the electric field (single layer/hybrid-stacked layers) is constructed from 45° quad-rotated dipole arms of sensors. The total ACS is enhanced to 2.31 × 105 nm2 for the polarization-insensitive single-layer sensor and 6.76 × 105 nm2 for the polarization-insensitive hybrid-stacked layers sensor. Planar arrays of 3 × 3, 4 × 4, and 5 × 5 elements of the last sensor are investigated for absorption and sensitivity enhancement. Ethanol, acetone, nitrogen dioxide, and toluene gases are tested with a total ACS peak value of 8.7 × 106 nm2. The sensitivity is 895.5 nm/RIU for 4 × 4 array elements.