Gap plasmon based on 2D MXene for broadband surface enhanced infrared absorption spectroscopy

With extreme field confinement in an ultrathin conducting layer, plasmons in 2D materials exhibit strong light-matter interactions, enabling the exploration of molecular vibration modes, specifically in infrared (IR) absorption spectroscopy. However, since high sensitivity in plasmons often results in a shorter resonant bandwidth, detecting molecular fingerprints across a broadband spectrum becomes fundamentally limited. Here, we demonstrate broadband surface-enhanced IR absorption (SEIRA) spectroscopy using a 2D materials-based gap plasmon resonator, specifically adopting Ti3C2Tx MXene. Within the MXene(Ti3C2Tx)-insulator(SiO2)-metal(Au) nanostructures, the MXene-based gap plasmon (MGP) modes are produced across the entire mid-IR spectrum. These modes exhibit a wavelength reduced by more than ten-fold compared to the wavelength in a vacuum, amplifying the light-matter interactions. Furthermore, using the MGP resonator, we demonstrate sensing of vibrational mode in polymethylmethacrylate (PMMA). This finding reveals that the MGP resonator can sensitively detect molecular fingerprints of the PMMA across the entire MIR range. Notably, the MGP resonator can also identify C-H bonding in the SWIR range, a detection that is challenging for other 2D material plasmonic devices. Our findings pave the way for developing sensitive sensors for the broadband spectrum and other optical applications in the SWIR range.