  We investigate the electronic properties of a graphene and $\alpha$-ruthenium
trichloride (hereafter RuCl$_3$) heterostructure, using a combination of
experimental and theoretical techniques. RuCl$_3$ is a Mott insulator and a
Kitaev material, and its combination with graphene has gained increasing
attention due to its potential applicability in novel electronic and
optoelectronic devices. By using a combination of spatially resolved
photoemission spectroscopy, low energy electron microscopy, and density
functional theory (DFT) calculations we are able to provide a first direct
visualization of the massive charge transfer from graphene to RuCl$_3$, which
can modify the electronic properties of both materials, leading to novel
electronic phenomena at their interface. The electronic band structure is
compared to DFT calculations that confirm the occurrence of a Mott transition
for RuCl$_3$. Finally, a measurement of spatially resolved work function allows
for a direct estimate of the interface dipole between graphene and RuCl$_3$.
The strong coupling between graphene and RuCl$_3$ could lead to new ways of
manipulating electronic properties of two-dimensional lateral heterojunction.
Understanding the electronic properties of this structure is pivotal for
designing next generation low-power opto-electronics devices.
