  The recent development of electron sensitive and pixelated detectors has
attracted the use of four-dimensional scanning transmission electron microscopy
(4D-STEM). Here, we present a precession electron diffraction assisted 4D-STEM
technique for automated orientation mapping using diffraction spot patterns
directly captured by an in-column scintillator based complementary
metal-oxide-semiconductor (CMOS) detector. We compare the results to a
conventional approach, which utilizes a fluorescent screen filmed by an
external CCD camera. The high dynamic range and signal-to-noise characteristics
of the detector largely improve the image quality of the diffraction patterns,
especially the visibility of diffraction spots at high scattering angles. In
the orientation maps reconstructed via the template matching process, the CMOS
data yields a significant reduction of false indexing and higher reliability
compared to the conventional approach. The angular resolution of misorientation
measurement could also be improved by masking reflections close to the direct
beam. This is because the orientation sensitive, weak and small diffraction
spots at high scattering angle are more significant. The results show that fine
details such as nanograins, nanotwins and sub-grain boundaries can be resolved
with a sub-degree angular resolution which is comparable to orientation mapping
using Kikuchi diffraction patterns.
