  We report three-dimensional (3D) structure determination of a twisted
hexagonal boron nitride (h-BN) heterointerface from a single-view data set
using multislice ptychography. We identify the buried heterointerface between
two twisted h-BN flakes with a lateral resolution of 0.57 {\AA} and a depth
resolution of 2.5 nm. The latter is a significant improvement (~2.7 times) over
the aperture-limited depth resolution of incoherent imaging modes such as
annular-dark-field scanning transmission electron microscopy. This is
attributed to the diffraction signal extending beyond the aperture edge with
the depth resolution set by the curvature of the Ewald sphere. Future advances
to this approach could improve the depth resolution to the sub-nanometer level
and enable the identification of individual dopants, defects and color centers
in twisted heterointerfaces and other materials.
