The combination of an atomic force microscope (AFM) and infrared laser illumination enables chemical-sensitive imaging with a spatial resolution orders of magnitude better than the diffraction limit. Nanoscale infrared microscopy and spectroscopy based on the mechanical detection of light-matter interactions has been a powerful tool to characterize chemical compositions and structures <i>in situ</i>. One increasingly popular technique, photoinduced force microscopy (PiFM), utilizes mechanical heterodyne probing of the resonant oscillations of an AFM cantilever. The only configuration reported is to tune the repetition rate of the infrared laser to match the frequency difference between the two mechanical modes of the cantilever. Our research group developed two new schemes (harmonic heterodyne detection and sequential heterodyne detection) to generalize the heterodyne configurations of PiFM. In harmonic heterodyne detection, the laser repetition rate matches integer fractions of the difference between two cantilever mechanical modes, while in sequential heterodyne detection, a mix of the laser repetition rate and an external polarization modulation matches the difference of the two mechanical modes. The two generalized heterodyne configurations preserve the high spatial resolution of PiFM and provide flexibilities for infrared nanoscopy. The applications of the generalized configurations of PiFM on the study of structured polymers, polaritonic materials, and biological samples will be covered.<br/>

Generalized heterodyne configurations for photoinduced force microscopy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.