Sensing mechanism of an Au-TiO₂-Ag nanograting based on Fano resonance effects

In recent years, with the development of nano-photonics, Fano resonance has gained increasing attention. Due to its high sensitivity, real-time detection, and label-free properties, the Fano resonance sensor has been widely applied in the fields of biochemistry and environmental detection. To improve the sensing characteristics of Fano resonance, an Au-TiO 2 -Ag grating structure is proposed in this paper, and the sensing performance is enhanced by a bi-metallic grating and deposited TiO 2 . The characteristics of both sensing and field distribution of the model are accordingly analyzed using the finite-difference time-domain method. By varying the structural parameters such as grating period, grating height, silver film thickness, and TiO 2 layer thickness, the tuning of sensing characteristics can be realized, and afterwards, the sensing performance is improved; consequently, the Fano resonance reflection spectrum with high sensitivity and a high figure of merit (FOM) value is obtained. When the grating period P = 200 nm, grating height T1 = 90 nm, silver film thickness T2 = 20 nm, TiO 2 layer thickness T3 = 20 nm, and SiO 2 layer thickness T4 = 600 nm, such a structure indicates favorable sensing performance, and sensor detection accuracy can reach 10 −3 ; maximum sensitivity is 1400 nm/RIU, and maximum FOM can reach 4212RIU −1 . The results demonstrate that the designed Fano resonance sensing model has good potential for application.

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