  Deviations from the perfect atomic arrangements in crystals play an important
role in affecting their properties. Similarly, diffusion of such deviations is
behind many microstructural changes in solids. However, observation of point
defect diffusion is hindered both by the difficulties related to direct imaging
of non-periodic structures and by the time scales involved in the diffusion
process. Here, instead of imaging thermal diffusion, we stimulate and follow
the migration of a divacancy through graphene lattice using a scanning
transmission electron microscope operated at 60 kV. The beam-activated process
happens on a timescale that allows us to capture a significant part of the
structural transformations and trajectory of the defect. The low voltage
combined with ultra-high vacuum conditions ensure that the defect remains
stable over long image sequences, which allows us for the first time to
directly follow the diffusion of a point defect in a crystalline material.
