  The convergent beam electron diffraction (CBED) patterns of twisted bilayer
samples exhibit interference patterns in their CBED spots. Such interference
patterns can be treated as off-axis holograms and the phase of the scattered
waves, meaning the interlayer distance can be reconstructed. A detailed
protocol of the reconstruction procedure is provided in this study. In
addition, we derive an exact formula for reconstructing the interlayer distance
from the recovered phase distribution, which takes into account the different
chemical compositions of the individual monolayers. It is shown that one
interference fringe in a CBED spot is sufficient to reconstruct the distance
between the layers, which can be practical for imaging samples with a
relatively small twist angle or when probing small sample regions. The quality
of the reconstructed interlayer distance is studied as a function of the twist
angle. At smaller twist angles, the reconstructed interlayer distance
distribution is more precise and artefact free. At larger twist angles,
artefacts due to the moir\'e structure appear in the reconstruction. A method
for the reconstruction of the average interlayer distance is presented. As for
resolution, the interlayer distance can be reconstructed by the holographic
approach at an accuracy of 0.5 A, which is a few hundred times better than the
intrinsic z-resolution of diffraction limited resolution, as expressed through
the spread of the measured k-values. Moreover, we show that holographic CBED
imaging can detect variations as small as 0.1 A in the interlayer distance,
though the quantitative reconstruction of such variations suffers from large
errors.
