Hybridized Phonon Polaritons Assisted Broad Range SEIRA-Based Multimolecular Sensing

In this work, we propose and theoretically investigate a van der Waals (vdWs) heterostructure for the detection of multiple analytes in the midinfrared (MIR) range (10.5–
$15 \mu \text{m}$
). The proposed hybrid structure consists of a 2-D silver grating and a thin slab of biaxial molybdenum trioxide (MoO
$_{{3}}{)}$
on top. Hybrid phonon polaritons (HPhPs) are formed by the strong coupling between magnetic polaritons (MPs) of silver grating and phonon polaritons of MoO3. Our structure is angle insensitive up to an incidence angle of 30° for both polarization directions. The tuning of HPhPs inside their respective Reststrahlen bands (RBs) is achieved by incorporating a monolayer of graphene. A wide-wavelength range from 10.5 to
$15 \mu \text{m}$
can be actively accessed by varying Fermi potential of graphene and incidence polarization. Moreover, by overlapping structural response with vibrational fingerprints of analytes, enhanced light–matter interaction [surface-enhanced IR absorption (SEIRA)-based sensing] is achieved, allowing the detection of minute amount of analytes (30 nm thick). We have numerically detected five different analytes (30 nm thick), namely, styrene, dimethyl methylphosphonate, polyethylene terephthalate, polystyrene, and ethanol, thereby proving the efficacy of our proposed vdWs heterostructure as highly sensitive multianalyte sensor.