Atomic resolution imaging of 3D crystallography in the scanning transmission electron microscope

Atomic resolution imaging in the scanning transmission electron microscope (STEM) has revolutionised science and technology, especially since the introduction of aberration correction ^1,2 , making sub-Ångström resolution easily realised. The ability to simply see two-dimensional projections of the atomic structure in thin specimens of crystalline solids has allowed unprecedented understanding of local features in nanostructures, such as interfaces, as well as of defects within materials and heterostructures ^3-5 . In specific cases, more information about the 3-dimensional structure can be determined by looking at multiple examples of the same structure using discrete tomography ^6-8 , or from conventional tilt-tomography, although the latter is hard to perform at atomic resolution ⁹ at reasonable fluence levels. Recently, however, major advances have been made in STEM with the advent of fast-readout direct electron detectors for 4DSTEM ^10,11 , which offers possibilities for novel imaging modalities not possible with monolithic annular ^12-14 , circular ¹⁵ or segmented detectors ^16,17 . We have previously shown that high angle electron diffraction into higher-order Laue zones produces an atomic resolution signal ¹⁸ , which reveals information about the 3D order in a crystal. This current work goes far beyond this and shows that the atomic resolution diffraction data contains information about the exact 3D orientation of one unique axis of the unit cell and the magnitudes of atom movements along it; and that this can be mapped at atomic resolution by fitting a simple mathematical model. In short, we show that by measuring and fitting high angle scattering, 4DSTEM can perform atomic resolution imaging of 3D crystal ordering without any need for sample tilting. Such approaches will provide a major step forward in understanding the details of nanoscale heterostructures, including surface reconstructions and interface structures.