Revealing Phonon Polaritons in Hexagonal Boron Nitride by Multipulse Peak Force Infrared Microscopy

Abstract Probing of polaritons in 2D materials is facilitated by spectroscopic imaging with nanometer spatial resolution. The combination of atomic force microscopy and infrared laser sources provides access for in situ mappings of phonon polaritons. Here, it is demonstrated that the photothermal‐based peak force infrared microscopy is capable of revealing phonon polaritons with high spatial resolution in isotopically pure hexagonal boron nitride microstructures without damaging the sample. To further improve the sensitivity, peak force infrared microscopy is enhanced with a scheme of multiple laser pulse excitation. The resulting method of multipulse peak force infrared microscopy can detect phonon polaritons with high sensitivity, which is particularly useful for probing polaritons in 2D materials with high damping characteristics.