  There has been extensive activity exploring the doping of semiconducting
two-dimensional (2D) transition metal dichalcogenides in order to tune their
electronic and magnetic properties. The outcome of doping depends on various
factors, including the intrinsic properties of the host material, the nature of
the dopants used, their spatial distribution as well as their interactions with
other types of defects. A thorough atomic-level analysis is essential to fully
understand these mechanisms. In this work, vanadium doped WSe$_2$ monolayer
grown by molecular beam epitaxy is investigated using four-dimensional scanning
transmission electron microscopy (4D-STEM). Through center of mass-based
reconstruction, atomic scale maps are produced, allowing the visualization of
both the electric field and the electrostatic potential around individual V
atoms. To provide quantitative insights, these results are successfully
compared with multislice image simulations based on ab initio calculations,
accounting for lens aberrations. Finally, a negative charge around the V
dopants is detected as a drop in the electrostatic potential, unambiguously
demonstrating that 4D-STEM can be used to detect and to accurately analyze
single dopant charge states in semiconducting 2D materials.
