Characterizing and visualizing heterogeneous compositions of various nanomaterials together with a nanoscale morphology is an essential part in a variety of disciplines of nanoscience and technology. The recent advanced photo-induced force microscopy (PiFM), which uses the opto-mechanical force between the sharp metal tip and the sample as the read-out mechanism to avoid the far-field background, has successfully visualized the heterogeneous nanomaterials with a chemical selectivity by a few nm spatial resolution [1-3]. The PiFM operates in the non-contact/tapping mode by monitoring the induced dipole force as well as the thermal expansion force mediated by van der Waals. The thermal response shows dissipative spectrum because of its absorptivity but the dipole response shows dispersive spectra because it is based on the refractive index. Unfortunately, because the thermal and the dipole responses are simultaneously manifested at the tip-sample junction under the light illumination condition, both of the interactions may be contributed to the system as different spectral origin. This leads that the origin of the chemical selectivity of the PiFM is often unclear [4]. Here, we shed a light on the origin of PiFM that is contributed by both of the thermal and the dipole response but they can be distinguished with respect to their experimental conditions. We provide the rigorous theoretical description for the thermal and dipole interaction based on the tip-enhanced absorption and image dipole method as well as the experimental demonstration.

Nanoscale spectroscopic studies by using tip-enhanced force: Dipole and thermal

2019 Fall National Meeting

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