Atomic electron tomography (AET) has become a powerful tool for atomic-scale structural characterization in three and four dimensions. It provides the ability to correlate structures and properties of materials at the single-atom level. With recent advances in data acquisition methods, iterative three-dimensional (3D) reconstruction algorithms, and post-processing methods, AET can now determine 3D atomic coordinates and chemical species with sub-Angstrom precision, and reveal their atomic-scale time evolution during dynamical processes. Here, we review the recent experimental and algorithmic developments of AET and highlight several groundbreaking experiments, which include pinpointing the 3D atom positions and chemical order/disorder in technologically relevant materials and capturing how atoms rearrange during early nucleation at four-dimensional atomic resolution.

Modern nanomaterials contain complexity that spans all three dimensions—from multigate semiconductors to clean energy nanocatalysts to complex block copolymers. For nanoscale characterization, it has been a long-standing goal to observe and quantify the three-dimensional (3D) structure—not just surfaces, but the entire internal volume and the chemical arrangement. Electron tomography estimates the complete 3D structure of nanomaterials from a series of two-dimensional projections taken across many viewing angles. Since its first introduction in 1968, electron tomography has progressed substantially in resolution, dose, and chemical sensitivity. In particular, scanning transmission electron microscope tomography has greatly enhanced the study of 3D nanomaterials by providing quantifiable internal morphology and spectroscopic detection of elements. Combined with recent innovations in computational reconstruction algorithms and 3D visualization tools, scientists can interactively dissect volumetric representations and extract meaningful statistics of specimens. This article highlights the maturing field of electron tomography and the widening scientific applications that utilize 3D structural, chemical, and functional imaging at the nanometer and subnanometer length scales.

The available x-ray brightness from accelerator-based light sources has been increasing at a rate faster than Moore’s Law. This is enabling new developments in x-ray tomography, using nanoscale x-ray beams on materials ranging in size from micrometers to centimeters. With scanning, one can record x-ray diffraction patterns to view nanoscale structure beyond the optic resolution, or fluorescence signals to study elemental distributions in three dimensions. These approaches are being used in various applications, for example, to study the redistribution of intrinsic metals in biological cells and tissues during biological processes, to compare as-fabricated versus as-designed integrated circuits, and to see the domain structure of soft ferromagnetic materials. While some applications face challenges, including radiation dose, new developments in sparse sampling and reconstruction algorithms, along with a new generation of diffraction-limited storage rings, offer exciting opportunities for materials research.