Surface-assisted single-crystal formation of charged colloids

Substrate-induced heterogeneous nucleation is a promising way to form an extended single crystal with few defects while controlling its direction. Despite its technological importance, however, the physics behind this process has remained elusive. By studying the kinetic pathway of crystal nucleation and growth at a single-particle level both experimentally and numerically, we reveal that the keys to substrate-induced monomorphic single-crystal formation are matching of the angular symmetry between locally favoured structures formed in a supercooled liquid and the most stable crystal and non-trivial coupling of the former to substrate-induced layering in the liquid. These two conditions are crucial for direct formation of the most stable crystal while keeping its unique direction relative to the substrate. We also discuss special features of charged systems. Our finding indicates that pre-ordering in a supercooled liquid state under the influence of a substrate largely dominates the course of future crystallization, providing new insights into the control of heterogeneous crystallization.