  Recent studies of secondary electron (SE) emission in scanning transmission
electron microscopes suggest that material's properties such as electrical
conductivity, connectivity, and work function can be probed with atomic scale
resolution using a technique known as secondary electron e-beam-induced current
(SEEBIC). Here, we apply the SEEBIC imaging technique to a stacked 2D
heterostructure device to reveal the spatially resolved electron orbital
ionization cross section of an encapsulated WSe2 layer. We find that the double
Se lattice site shows higher emission than the W site, which is at odds with
first-principles modelling of ionization of an isolated WSe2 cluster. These
results illustrate that atomic level SEEBIC contrast within a single material
is possible and that an enhanced understanding of atomic scale SE emission is
required to account for the observed contrast. In turn, this suggests that
subtle information about interlayer bonding and the effect on electron orbitals
can be directly revealed with this technique.
