Nucleation of colloidal crystals on configurable seed structures

Nucleation is an important stage in the growth of crystals. During this stage, the structure and orientation of a crystal are determined. However, short time- and length-scales make nucleation poorly understood. Micrometer-sized colloidal particles form an ideal model system to study nucleation due to more experimentally accessible time- and length-scales and the possibility to manipulate them individually. Here we report experiments and simulations on nucleation in the bulk of a hard-sphere fluid, initiated by seed structures configured using optical tweezers. We find that the defect topology of the critical nucleus determines the crystal morphology. From the growth of the crystals beyond the critical nucleus size, new insights into the role of defects in crystal growth were gained that are incompatible with the assumption of equilibrium growth. These results explain the complex crystal morphologies observed in experiments on hard spheres.