  The reduced dimensionality in two-dimensional materials leads a wealth of
unusual properties, which are currently explored for both fundamental and
applied sciences. In order to study the crystal structure, edge states, the
formation of defects and grain boundaries, or the impact of adsorbates, high
resolution microscopy techniques are indispensible. Here we report on the
development of an electron holography (EH) transmission electron microscopy
(TEM) technique, which facilitates high spatial resolution by an automatic
correction of geometric aberrations. Distinguished features of EH beyond
conventional TEM imaging are the gap-free spatial information signal transfer
and higher dose efficiency for certain spatial frequency bands as well as
direct access to the projected electrostatic potential of the 2D material. We
demonstrate these features at the example of h-BN, at which we measure the
electrostatic potential as a function of layer number down to the monolayer
limit and obtain evidence for a systematic increase of the potential at the
zig-zag edges.
