Imaging Negative\nCharge around Single Vanadium Dopant\nAtoms in Monolayer Tungsten Diselenide Using 4D Scanning Transmission\nElectron Microscopy

There has been extensive activity exploring the doping\nof semiconducting\ntwo-dimensional (2D) transition metal dichalcogenides in order to\ntune their electronic and magnetic properties. The outcome of doping\ndepends on various factors, including the intrinsic properties of\nthe host material, the nature of the dopants used, their spatial distribution,\nas well as their interactions with other types of defects. A thorough\natomic-level analysis is essential to fully understand these mechanisms.\nIn this work, the vanadium-doped WSe<sub>2</sub> monolayer grown by\nmolecular beam epitaxy is investigated using four-dimensional scanning\ntransmission electron microscopy (4D-STEM). Through center-of-mass-based\nreconstruction, atomic-scale maps are produced, allowing the visualization\nof both the electric field and the electrostatic potential around\nindividual V atoms. To provide quantitative insights, these results\nare successfully compared to multislice image simulations based on\nab initio calculations, accounting for lens aberrations. Finally,\na negative charge around the V dopants is detected as a drop in the\nelectrostatic potential, unambiguously demonstrating that 4D-STEM\ncan be used to detect and to accurately analyze single-dopant charge\nstates in semiconducting 2D materials.