Electron Ptychography of 2D Moiré Superlattices

Electron microscopy and atomic-scale materials characterization are undergoing a revolution fueled by the new capabilities of electron ptychography, which is setting records for spatial resolution down to 20 picometers. Here, we will demonstrate atomically precise methods to characterize 2D materials using electron ptychography. We use ptychography to image the 3D structure of moiré materials, focusing on twisted transition metal dichalcogenides. Using this approach, we are able to access atomic coordinates with picometer-scale precision, extract detailed strain profiles, and visualize the atomic reconstructions at soliton-like stacking faults, and the moiré structures evolve with twist angle. By tilting the samples and utilizing the extremely high resolution of ptychography we are able to access both in- and out-of-plane features of the moiré structures, including local tilt, 3D rippling, and the interlayer interactions.