3D Mapping of Defects and Moiré Corrugations via Electron Ptychography Atomic Coordinate Retrieval

Abstract: Defects and reconstructions in 2D moir\'e materials cause out-of-plane deformations which strongly modify their electronic properties but are difficult to experimentally access. Here, we solve the 3D atomic coordinates of twisted bilayer WSe$_2$ with picometer-scale accuracy using multislice electron ptychography (MEP) acquired from a single orientation. The resulting atomic models individually visualize each of the six atomic planes, revealing the curvature of each WSe$_2$ layer, variations in the interlayer spacing, and the 3D locations of individual vacancies -- which lie exclusively in the outer Se planes. We also observe a new, unexpected type of structural disorder consisting of mixed bending -- and breathing-type moir\'e-induced corrugations that should strongly impact the emergent electronic properties. Broadly, our methods generate 3D atom-by-atom models of a 2D heterointerface from data acquired in about 30 seconds, methods that should unlock routine access to 3D atomic information in 2D systems and catalyze design methods to control out-of-plane deformations.