Defect structures serve as nucleation sources that allow growth and evolution of structure at temperatures far lower than perfect crystalline structure would allow. Screw dislocations, which form spiral growth/etch patterns when they evolve freely on a thin film surface, are the classical example of this behavior. Nanoscalecrystalline structures provide a mechanism for capturing the spiraling dislocation within the boundaries of thenanostructure. Such a trapped trapped structure no longer can spiral freely, and instead develops a periodic structure with a highly non-uniform angular frequency. Very simple physical phenomena -the free energy of a curved interface, and the Brownian motion of atoms at the dislocation edge, suffice to model the behavior quantitatively.
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