Photoinduced Atomic Force Spectroscopy and Imaging of Two-Dimensional Materials

We report on the near-field imaging of atomically thin layers of two-dimensional (2D) materials using photoinduced force mapping. This is accomplished by modifying a traditional atomic force microscopy set up to detect optical forces between a nanoscale tip and a photoexcited sample. Our set up facilitates the imaging of few-layer flakes ofMoS(2) or WS2 and the simultaneous acquisition of optical force spectra, both in ambient and vacuum conditions. The evaluated force spectra in both samples exhibit the characteristic excitonic resonance peaks that are most typically observed in far-field absorption spectroscopy. We also show that nanoscale defect sites and flake edges can be distinguished from the crystalline surfaces with a high spectral resolution. Our results pave the way toward gaining a wholesome understanding of optical interactions and structure-property correlations in 2D materials and their heterostructures.