  Atomic-resolution scanning transmission electron microscopy (STEM)
characterization requires precise tilting of the specimen to high symmetric
zone axis, which is usually processed in reciprocal space by following the
diffraction patterns. However, for small-sized nanocrystalline materials, their
diffraction patterns are too faint to guide the tilting process. Here, a simple
and effective tilting method is developed based on the diffraction contrast
change of the shadow image in the Ronchigram. We can calculate the
misorientation angle of the specimen and tilt it to the zone axis based on the
position of the shadow image with lowest intensity. This method requires no
prior knowledge of the sample and the maximum misorientation angle we can
correct is greater than +-6.9 degree with sub-mrad accuracy. It is processed in
real space, without recording the diffraction patterns of the specimens, which
can effectively apply to nanocrystalline materials. Combined with the scripting
to control the microscope, we can automatically tilt the sample to the zone
axis under low dose condition (<0.17 e-/A2/s), which could facilitate the
imaging of beam sensitive materials such as zeolites or metal organic
frameworks. This automated tilting method could contribute to the atomic-scale
characterization of the nanocrystalline materials by STEM imaging.
