Direct observation of 3D atomic packing in monatomic amorphous materials

TL;DR

This study uses advanced atomic electron tomography to directly visualize the 3D atomic structure of monatomic amorphous materials, revealing prevalent pentagonal bipyramids and their networks, which enhances understanding of amorphous states.

Contribution

First direct 3D atomic imaging of monatomic amorphous materials, uncovering atomic motifs and network structures with implications for phase transition studies.

Findings

Pentagonal bipyramids are the most common atomic motifs.

Pentagonal bipyramids form extended networks rather than icosahedra.

Networks grow and evolve during the liquid-to-glass transition.

Abstract

Liquids and solids are two fundamental states of matter. However, due to the lack of direct experimental determination, our understanding of the 3D atomic structure of liquids and amorphous solids remained speculative. Here we advance atomic electron tomography to determine for the first time the 3D atomic positions in monatomic amorphous materials, including a Ta thin film and two Pd nanoparticles. We observe that pentagonal bipyramids are the most abundant atomic motifs in these amorphous materials. Instead of forming icosahedra, the majority of pentagonal bipyramids arrange into networks that extend to medium-range scale. Molecular dynamic simulations further reveal that pentagonal bipyramid networks are prevalent in monatomic amorphous liquids, which rapidly grow in size and form icosahedra during the quench from the liquid state to glass state. The experimental method and results are expected to advance the study of the amorphous-crystalline phase transition and glass transition at the single-atom level.