Probing the dynamics of nanoparticle formation from a precursor at atomic resolution.

Control of reduction kinetics and nucleation processes is key in materials synthesis. However, understanding of the reduction dynamics in the initial stages is limited by the difficulty of imaging chemical reactions at the atomic scale; the chemical precursors are prone to reduction by the electron beams needed to achieve atomic resolution. Here, we study the reduction of a solid-state Pt precursor compound in an aberration-corrected transmission electron microscope by combining low-dose and in situ imaging. The beam-sensitive Pt precursor, K2PtCl4, is imaged at atomic resolution, enabling determination of individual (K, Pt, Cl) atoms. The transformation to Pt nanoclusters is captured in real time, showing a three-stage reaction including the breaking of the ionic bond, formation of PtCl2, and the reduction of the dual-valent Pt to Pt metal. Deciphering the atomic-scale transformation of chemicals in real time using combined low-dose and in situ imaging brings new possibility to study reaction kinetics in general.