Front Cover: Structure Matters – Direct In‐situ Observation of Cluster Nucleation at Atomic Scale in a Liquid Phase (2/2021)

Seeing how particles form: The synthesis of nanoparticles starts with the nucleation of atomic clusters. We directly observe the initial steps of Pt clusters nucleating in ionic liquid by using transmission electron microscopy, by inducing nucleation in carbon-supported nanodroplets with a high concentration of Pt monomers. Initially, few-atom clusters nucleate, which then grow and coalesce to form disordered cluster agglomerates and spherical particles. There are briefly metastable close-packed cluster structures at the few-atom scale, but long-term stable crystallinity appears first at cluster sizes above 1 nm. More information can be found in the Communication by Trond Henninen, Debora Keller, and Rolf Erni.