APPLICATIONS OF MULTI-MODAL ATOMIC FORCE MICROSCOPE IN 2D TRANSITION METAL DICHALCOGENIDES

Abstract

The multi-mode AFM has been proved to be a powerful characterization tool. The heterogenous distribution of intrinsic defects in the as-grown TMDs can be unambiguously unveiled using the Kelvin probe force microscopy (KPFM), with the findings further being corroborated by scanning transmission electron microscopy (STEM) and density functional theory (DFT) calculations. Moreover, a defect-related conductivity map of the sample is also revealed by the PeakForce tunneling atomic force microscopy (PF-TUNA). In addition to defects, the evolution of interlayer coupling strength in twisted TMDs can also be revealed by its work function variation using the KPFM, while the moiré superlattices in these twisted TMDs can be visualized with Piezoresponse force microscopy (PFM), through the flexoelectric effect from the polarized domain walls. Beyond its characterization capabilities, AFM is also demonstrated as a sophisticated manipulation tool to 2D materials. Utilizing the force between tip and sample surfaces, we can either exert a dynamic control of the orientation between the layers, or tune the interlayer coupling strength in a vdW bilayer structure. Finally, careful studies of the exciton behaviors in response to defect, strain, twisting angle and interlayer coupling, will also be illustrated in this dissertation.