Infrared nano-spectroscopy and imaging on spatially confined nanomaterials

Abstract As materials become spatially confined, their electronic and optical properties deviate significantly from those of their bulk counterparts. In this review article, we highlight our recent applications of infrared scattering scanning near-field optical microscopy (IR s-SNOM) to explore the distinct characteristics of nanoconfined materials, providing insights into confinement-induced behavior and light–matter interactions at the single-nanometer scale to sub-micron mesoscale. We specifically discuss the direct observation of phase transitions in individual nanoparticles through local optical conductivity measurements, the characterization of infrared vibrational modes at the single-protein level, and ultrafast nano-imaging of local electron–hole dynamics in transition metal dichalcogenide flakes. Collectively, these applications underscore the versatility of IR s-SNOM in elucidating the unique properties of diverse nanomaterials, ranging from correlated and low-dimensional materials to biological molecules.