Surface effects on heterogeneous nucleation of metal at the atomic scale

Agglomerationand crystallization of atoms are the key processes in nucleation. For heterogeneous nucleation, investigating the influence of the substrate surface on agglomeration and crystallization, and then understanding the related mechanism at the atomic scale is crucial to material synthesis. Here, electron beam in transmission electron microscopy is utilized to decompose BiOCl material for generating dissociative Bi atoms. We observe the heterogeneous nucleation process of Bi nanocrystals at the surface of BiOCl from the side view with atomic spatial resolution and millisecond temporal resolution. The nucleation and crystallization of Bi nanocrystal is found to occur at the concave sites of the surface with angles ranging from 91° to 157° and form stable nucleus with sizes of 1 to 2 nanometers, while the pre-agglomerated Bi clusters dissociate again on the flat and convex surface. We demonstrate the collision between the Bi atoms and the concave structure helps Bi atoms release kinetic energy and form nucleus, and then the concave surface further stabilizes the nucleus and promotes crystallization.