  There is only a handful of scanning techniques that can provide surface
topography at nanometre resolution. At the same time, there are no methods that
are capable of non-invasive imaging of the three-dimensional surface topography
of a thin free-standing crystalline material. Here we propose a new technique -
the divergent beam electron diffraction (DBED) and show that it can directly
image the inhomogeneity in the atomic positions in a crystal. Such
inhomogeneities are directly transformed into the intensity contrast in the
first order diffraction spots of DBED patterns and the intensity contrast
linearly depends on the wavelength of the employed probing electrons.
Three-dimensional displacement of atoms as small as 1 angstrom can be detected
when imaged with low-energy electrons (50 - 250 eV). The main advantage of DBED
is that it allows visualisation of the three-dimensional surface topography and
strain distribution at the nanometre scale in non-scanning mode, from a single
shot diffraction experiment.
