In Situ Microscopic Observation on Surface Kinetics in Optical Trapping-Induced Crystal Growth: Step Formation, Wetting Transition, and Nonclassical Growth

Optical trapping-induced crystallization (OTIC) has provided significant impacts on the control of crystallization. Although consecutive research studies have implied that the optical potential formed on the crystalline surface by light propagation contributes to the crystal growth by observing bulk crystal growth, direct observation from the viewpoint of the surface kinetics represented as Burton, Cabrera, and Frank theory is still lacking. Here, we directly show the surface state modification by microscopically observing step formation/dissolution and wetting transition of a solution thin layer over a sodium chlorate crystalline surface upon turning on/off the laser irradiation. Irradiating/stopping of the laser irradiation to the crystal led to the formation/dissociation of several tens of micron-sized islands constructed by bunched steps. It was also found that the wetting transition of the solution thin film over the entire crystal surface took place simultaneously with the laser irradiation, evidencing that the interfacial potential was modified from repulsive to attractive potential by light propagation. Moreover, the observation visualized nonclassical crystal growth like the cluster assimilation scenario. Our observation not only leads to a deeper understanding of the mechanism of OTIC but also can provide the opportunity to reach unusual crystal growth phenomena beyond the classical limit and has implications for crystal growth modified by an external field.