AET principle and recent progress. (A) A schematic layout of AET, showing how AET works from data acquisition, image pre-processing, reconstruction to atom tracing model. (B) 3D positions of individual atoms in a tungsten needle sample revealed by AET. Atoms in different layers are colored differently (Adapted from ref. [160]. Copyright©2015, Springer Nature). (C) Overview of the 3D positions of individual atomic species with Fe atoms in red and Pt atoms in blue. 6569 iron and 16,627 platinum atoms are classified in this work (Adapted from ref. [62]. Copyright©2017, Springer Nature). (D) Capturing 4D atomic nucleation with AET. Growing (top), fluctuating (middle) and dissolving (bottom) nuclei are tracked at different annealing times (Adapted from ref. [63]. Copyright©2019, Springer Nature).