Metamaterial of sodium-graphene for bifunctional perfect absorber

In this paper, a bifunctional metamaterial perfect absorber (MPA) by combining sodium and graphene with the two-dimension grating structure is proposed, which can serve as both a tunable absorber and a refractive index sensor. The proposed MPA can achieve perfect absorption for near-infrared light by combining the finite-difference time-domain (FDTD) method and the impedance matching principle for optimization. The calculation results of the FDTD and the finite element method are in good agreement. The perfect absorption of the MPA is well explained by the electric and magnetic field distribution attributed to the metal assisted guided-mode resonance. Furthermore, the simulation results indicate that the peak modulation depth of MPA achieves 61.99% by tuning the chemical potential of graphene. In terms of sensing performance, the MPA has a figure of merit value of 284 RIU−1, which is a substantial advancement compared with the sensors reported previously. By virtue of the structural simplicity, polarization-insensitivity, tunable absorption efficiency, high sensitivity, and long penetration depth, the MPA offers a wide range of applications in the fields of photoelectric detection, photoelectric modulation, biology, and chemistry.