▎ 摘　　要

In this paper, we propose a graphene-assisted plasmonic metamaterial absorber to operate as an ultra-compact optical gas sensor in the infrared (IR) region. The metamaterial absorber is comprised of a thin silicon-dioxide layer that is middling between a gold film and an array of graphene-coated gold nano-disks. Using the finite element method, we investigate the resonance characteristics of the proposed plasmonic metamaterial and show that the metamaterial has three distinct resonances in visible and infrared regions. We demonstrate that the strongest absorption peak of the proposed metamaterial is attributed to a fundamental localized surface plasmon resonance in IR, which has also the highest spectral sensitivity to the refractive index (RI) variations of the surrounding medium. The sensing mechanism is based on evaluation of gaseous medium RI surrounding the nano-disks, by illuminating the metamaterial with IR radiation and subsequently measuring the reflection or absorption spectra of the structure. We show that graphene coating of the gold nano-disks improves the sensitivity of the metamaterial to the gas RI by more than two times. Using the optimized design parameters, an average linear spectral sensitivity of 720 nm/RIU and an approximate detection limit of 1 x 10(-5) RIU has been obtained for gas RI variations between 1 and 1.05. We also show that the proposed sensor has a linear response even for extremely small variations in gas RI in the order of 10(-5) RIU. The proposed metamaterial configuration is relatively easy to fabricate and can be used to monitor low concentrations of various gases in different applications ranging from environmental monitoring to home safety monitoring systems.