The development of twisted van der Waals (vdW) heterostructures—where layers of 2D materials are stacked with controlled rotation angles—has opened exciting opportunities in quantum technologies. Notably, the twist interfaces in hexagonal boron nitride (h-BN) can undergo structural transformations that support single-photon emission, making them promising for quantum sensing. However, imaging these buried interfaces using scanning transmission electron microscopy (STEM) has been challenging due to poor signal quality and geometric constraints.
In this work, we demonstrated the use of multislice ptychography (MSP), a sensitive coherent diffractive imaging technique, to visualize a twisted h-BN interface from a single-view dataset. STEM experiments were conducted on the TEAM I microscope at the National Center for Electron Microscopy, LBNL, where we acquired diffraction patterns from a 12-nm-thick twisted h-BN sample. Unlike conventional ptychographic approaches that yield a single complex image of the sample, MSP enables depth-sectioning during post-processing, producing a series of reconstructed image slices.
We successfully reconstructed 24 slices of the twisted h-BN heterostructure, resolving the top flake, interface, and bottom flake with a lateral resolution of 0.57 Å. Remarkably, a depth resolution of 2.5 nm was achieved without sample tilting—the highest reported depth resolution at the time of publication. This work highlights MSP’s potential to resolve nanoscale features in three dimensions without requiring tomographic data acquisition, paving the way for advanced quantum materials characterization.