Tomographic and multimodal scattering-type scanning near-field optical microscopy with peak force tapping mode.

Scattering-type scanning near-field optical microscopy (s-SNOM) enables nanoscale spectroscopic imaging and has been instrumental for many nano-photonic discoveries and in situ studies. However, conventional s-SNOM techniques with atomic force microscopy tapping mode operation and lock-in detections do not provide direct tomographic information with explicit tip-sample distance. Here, we present a non-traditional s-SNOM technique, named peak force scattering-type scanning near-field optical microscopy (PF-SNOM), by combination of peak force tapping mode and time-gated light detection. PF-SNOM enables direct sectioning of vertical near-field signals from a sample surface for both three-dimensional near-field imaging and spectroscopic analysis. Tip-induced relaxation of surface phonon polaritons are revealed and modeled by considering tip damping. PF-SNOM also delivers a spatial resolution of 5 nm and can simultaneously measure mechanical and electrical properties together with optical near-field signals. PF-SNOM is expected to facilitate three-dimensional nanoscale near-field characterizations and correlative in situ investigations on light-induced mechanical and electrical effects.