Probing Mid-Infrared Phonon Polaritons in the Aqueous Phase.
basic_science · Level V
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- Record sourced from PubMed, PMID 32320254.
- Also identified by DOI 10.1021/acs.nanolett.0c01199.
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Abstract
Phonon polaritons (PhPs) are collective phonon oscillations with hybridized electromagnetic fields, which concentrate mid-infrared optical fields that can match molecular vibrations. The utilization of PhPs holds the promise for chemical sensing tools and polariton-enhanced nanospectroscopy. However, investigations and innovations on PhPs in the aqueous phase remain stagnant because of the lack of <i>in situ</i> mid-infrared nanoimaging methods in water. Strong infrared absorption from water prohibits optical delivery and detection in the mid-infrared for scattering-type near-field microscopy. Here, we present our solution: the detection of photothermal responses caused by the excitation of PhPs by liquid phase peak force infrared (LiPFIR) microscopy. Characteristic interference fringes of PhPs in <sup>10</sup>B isotope-enriched <i>h</i>-BN were measured in the aqueous phase and their dispersion relationship extracted. LiPFIR enables the measurement of mid-infrared PhPs in the fluid phase, opening possibilities and facilitating the development of mid-IR phonon polaritonics in water.