strobeadmin

Crystals form in storm clouds, metals, drug molecules, and even in diseased tissues. Despite their ubiquity, scientists still don’t fully understand what happens when a liquid solution first starts to form a solid crystal, a step called nucleation. Now researchers have gotten their first glimpse of the details of the process, imaging individual atoms during nucleation in metal nanoparticles (Nature 2019, DOI: 10.1038/s41586-019-1317-x).

For the first time scientists have watched iron and platinum atoms crystallise in 4D – not only observing their arrangement in space but tracking them over time. Their observations clash with classical nucleation theory, which describes the early stages of a phase transition, adding to growing evidence that the textbook theory is outdated and imprecise.

Results of UCLA-led study contradict a long-held classical theory.

Everyday transitions from one state of matter to another — such as freezing, melting or evaporation — start with a process called “nucleation,” in which tiny clusters of atoms or molecules (called “nuclei”) begin to coalesce. Nucleation plays a critical role in circumstances as diverse as the formation of clouds and the onset of neurodegenerative disease.

A UCLA-led team has gained a never-before-seen view of nucleation — capturing how the atoms rearrange at 4D atomic resolution (that is, in three dimensions of space and across time). The findings, published in the journal Nature, differ from predictions based on the classical theory of nucleation that has long appeared in textbooks.