Bound-state-in-the-continuum (BIC) induced narrow resonances in MXene-coated absorptive dielectric metasurfaces for Methane sensing

Strong light confinement is highly necessary for various applications, including sensing. MXene, a novel and emerging material with a broadband plasmonic response, has been highly utilized in electronic sensing systems, as well 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, narrow and high absorption resonance of quality factor of $\sim$150 is attained, where MD is the dominant multipole, governed by symmetry-protected BIC. Both hybrid metasurface designs are optimized to exhibit narrow resonance in the vicinity of 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 the spacer layer of $SiO_2$. The spectral characteristics of the designed metasurface can be utilized 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.