Graphene-based tunable dual symmetric bound states in the continuum metasurface- implications in nanoscale high sensitivity sensing

In this paper, we have proposed a graphene-based dual symmetric bound states in the continuum (BIC) metasurface. On an all-graphene platform, we have shown that by breaking the symmetry in two ways, one can simultaneously access dual quasi-BIC (Q-BIC) spectra. The unit cell of the metasurface consists of the graphene etch patterned circles of equal radius on a dielectric substrate. The placement of the pattern is such that the structure is symmetric. By perturbing the radius of the circle at these symmetric positions, the asymmetry is introduced to access the first Q-BIC. Another way of accessing the Q-BIC spectra is to perturb the symmetric positions, maintaining the equal radii of the etched circles. Combining these two strategies, one can access the dual QBIC spectra based on the wavelength range of interest. Moreover, graphene is tunable with the control of its chemical potential. We have demonstrated our tunable structure at the MID-IR region in the transmission mode of operation. All the device dimensions are in the sub-wavelength range. The Q-factor of these plasmonic Q-BIC transmission dips has moderate values that hold wide prospects in sensing applications. For our proposed structure, we have shown application in nanoscale sensing of hazardous solvents like nitrobenzene and hazardous gases like methane, considering the experimental dispersion data. A minimum limit of detection (LOD) of 0.025 RIU and 0.0068 RIU has been reported for nitrobenzene and methane.