Polymorphic Crystalline Layer at the Crystallization Front.

The morphology and kinetics of the crystal growth front have been poorly explored at the particle level. Here, we experimentally observe the crystal growth front in liquid with single-particle kinetics using colloid systems and reveal a surface layer of polymorphic crystal near the solid-solid transition when the two crystals form a low-energy coherent interface. The thickness of the surface crystal can exceed 50 particles and grows logarithmically with the temperature as approaching the solid-solid transition which follows premelting theory. The liquid-crystal interface grows continuously through random attachments of diffusive particles, while the crystal-crystal interface exhibits a martensitic growth with collective motions. The presence of a surface crystalline layer reduces defect density, which is helpful in crystal fabrication.