Bound state in the continuum induced narrow resonances in MXene-coated absorptive dielectric metasurfaces for methane sensing

Strong light confinement is essential for a range of applications, including sensing. MXene, a novel and emerging material with a broadband plasmonic response, active tunability, versatile surface chemistry with high adsorption efficiency, and flexibility, has been widely used in electronic sensing systems and has garnered significant attention for its applicability in photonics. The loss imparted by MXene can be overcome through the Bound States in Continuum (BIC) physics. In this work, we report two important designs of a hybrid metasurface, comprising a Silicon nanodisk metasurface and MXene. In both designs, a narrow and high absorption resonance of quality factor of ∼150 is attained, where magnetic dipole is the dominant multipole, governed by symmetry-protected BIC. Both hybrid metasurface designs are optimized to exhibit a narrow resonance near 1650 nm with an absorption greater than 90%. The origin of high absorbance in such a hybrid metasurface is attributed to the momentum matching by SiO2 spacer layer. The spectral characteristics of the designed metasurface can be used for first-overtone spectroscopy of methane gas. Numerical simulations yield a bulk refractive index sensitivity of 171 nm/RIU with FOM = 17.56 RIU−1 and sensitivity for methane gas, S = 0.8 nm per unit percentage concentration, when a Cryptophane-E layer is used. The designed sensor can also be tuned by varying the voltage across the MXene layer.