Kinetic development of crystallization fronts in complex plasmas

Although it is relatively straightforward to measure the atomic structure of crystals, the detailed dynamics of crystal growth (including the evolution of self-organization, structure formation, and the associated kinetic and thermodynamic development) remains one of the most important topics of solid-state physics. Very little is known, for instance, about the evolutionary paths of crystal structure development, and the structural complexity of the surface down to atomic dimensions and its change with time. This is, to a large extent, due to the lack of suitable systems that can be studied at the appropriate length- and timescales. Here, we report experimental observations of a crystallization front propagating in a supercooled region of a three-dimensional fluid complex plasma. The structure and evolution of the front are analysed using kinetic measurements of individual microparticle dynamics. It is found that the fluid-crystalline transition is accompanied by short-lived 'nano'-crystallites in the fluid and 'nano'-droplets in the crystalline phases, that the surface structure is scale-free (fractal) in the experimentally accessible regime (2-10 lattice distances) and that crystal growth follows a universal self-organization pattern at the particle level, leading to oscillations in the surface roughness. © 2006 Nature Publishing Group.