Three-dimensional imaging of buried interfaces in twisted hexagonal boron nitride

The development of twisted van der Waals heterostructures, where individual layers of 2D materials are successively stacked at relative rotation angles, has led to exciting applications in optoelectronics, sensing, energy storage, quantum computing and more [1]. However, it remains a major challenge to determine the 3D locations of point defects at the buried interfaces of twisted 2D heterostructures. Here we demonstrate the application of multislice ptychography [2], a coherent diffractive imaging technique [3], to a twisted hexagonal boron nitride (hBN) 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 [4], which is a significant improvement over the aperture-limited depth resolution of 6.73 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 [5]. Future advances to this approach could improve the depth resolution to the near atomic level and enable the identification of individual dopants, defects and color centers in twisted heterointerfaces and other materials.

1. A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013).

2. Z. Chen et al. Science 372, 826 (2021).

3. J. Miao et al. Nature 400, 342 (1999).

4. C. O’Leary et al. arXiv:2308.15471 (2023).

5. K. S. Raines et al. Nature 463, 214 (2010).