3D atomic positions and atom packing in monatomic amorphous solids (Adapted from ref. [61]. Copyright©2022, Springer Nature). (A) Experimental 3D atomic model of an amorphous Ta film (left) and two Pd nanoparticles (Pd1, middle; Pd2, right) with surface crystal nuclei in grey. The three insets show the average 2D power spectra of the experimental images for the Ta film and two Pd nanoparticles, where the amorphous halos are visible. Scale bars: 2 nm. (B) A slice through the Ta film (left) and two Pd nanoparticles (Pd1, middle; Pd2, right) shows the local mass density heterogeneity (color) overlaid with polytetrahedral packing (black). Scale bar: 2 nm.