Imaging 2D Moirés at Deep Sub-Angstrom Resolution

A challenge in the study of 2D moirés is that they are highly inhomogenous across length scales, containing defects and strains that vary from site-to-site. In addition, solving the atomic structure is challenging because atoms in the moiré are separated by sub-angstrom distances in projection images, thus requiring deep sub-angstrom spatial resolution. While electron ptychography has demonstrated access to the deep sub-angstrom regime, this technique has required expensive, delicate aberration-corrected electron microscopes. Here, we demonstrate sub-angstrom resolution electron ptychography of 2D materials in an uncorrected scanning transmission electron microscopy (STEM). We demonstrate the power and flexibility of electron ptychography by showing that it can achieve sub-angstrom resolution across a broad range of microscope conditions to uncover details of the moiré structure. Counterintuitively, we find that geometric aberrations actually benefit electron ptychography because they produce structured beams that are more dose-efficient for ptychography than focused, aberration-free probes. This work should dramatically expand the ability to study 2D moirés with atomic precision.