Light Polarization Effects of Chemical Sensing in the Mid-Infrared Region Using ZnO: Ga-Based Plasmonic Surface Lattice Resonances

Plasmonic surface lattice resonance (plasmonic SLR) is a remarkable platform for chemical-specific detection based on surface-enhanced infrared absorption (SEIRA). In this study, we investigated polarized reflectance spectra of plasmonic SLR comprising Ga-doped ZnO (ZnO:Ga) two-dimensional microdot arrays to understand the relationship between light polarization and SEIRA. The periodicity of the microdot arrays was varied to elucidate the optical processes involved in plasmonic SLRs depending on the light polarization. In particular, the out-of-plane polarization induced optical interactions between the propagated surface plasmon polariton (SPP) and diffractive waves scattered from the microdot arrays, resulting in a higher electric field on the microdot surfaces than that under in-plane polarization, which was attributed to the coupling between localized SPR and diffractive waves. This difference in the optical excitation significantly affected the optical properties of the ZnO-based SPR and its SEIRA performance. Finally, we demonstrated high sensitivity SEIRA detection at the monolayer scale using self-assembled layers. We found that the light polarization control is effective in improving the ZnO-based SPR and SEIRA effects. This study demonstrates the importance of light polarization in enhancing SEIRA.