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, the vanadium-doped WSe2 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 to 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.