Fig. 1. Schematic diagram of dipole model

Fig. 2. Calculated curve of gradient force varying with probe-sample distance

Fig. 3. Schematic diagram of THz PiFM

Fig. 4. Optical micrograph of monolayer MoS₂ grains

Fig. 5. Topography, THz PiFM and THz s-SNOM micrograph of MoS₂

Fig. 6. The height and PiFM signal at the edge of MoS₂ under optical excitation

Fig. 7. Scanning electron microscopy and micro-PL characterizations of MoS₂