Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric-dipole limit. Recently, SHG has attracted widespread interest as versatile and noninvasive tool for characterization of crystal emerging ferroic or topological orders quantum materials. However, conventional far-field optics unable to probe local at deep subwavelength scale. Here, near-field imaging 2D semiconductors heterostructures with spatial resolution down 20 nm demonstrated using scattering-type nano-optical apparatus. It shown that efficiency greatly enhanced by excitons atomically thin transition metal dichalcogenides. Furthermore, correlating linear nano-imaging, nanoscale variations interlayer stacking order bilayer WSe2 are resolved, stacking-tuned excitonic light–matter interactions revealed. This work demonstrates interrogation structure–property relationships nanometer length scales relevant properties