Three-dimensional imaging of embedded interfaces with multislice ptychography

We demonstrate the application of multislice ptychography to a twisted hexagonal boron nitride (h-BN) heterointerface from a single-view data set. The propagation from the top flake, through the interface, to the bottom flake is visualized from separate slices of the reconstruction. The depth resolution of the reconstruction is determined to be 2.74 nm, which is a significant improvement over the aperture-limited depth resolution of 6.74 nm. 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.