Wedding Cake Growth Mechanism in One-Dimensional and Two-Dimensional Nanostructure Evolution.

The kinetic processes and atomistic mechanisms in nanostructure growth are of fundamental interest to nanomaterial syntheses with precisely controlled morphology and functionality. By programming deposition conditions at time domain, we observed the wedding cake growth mechanism in the formation of 1D and 2D ZnO nanostructures. Within a narrow growth window, the surfaces of the 1D and 2D structures were covered with a unique concentric terrace feature. This mechanism was further validated by comparing the characteristic growth rates to the screw dislocation-driven model. An interesting 1D to 2D morphology transition was also found during the wedding cake growth, when the adatoms overcome the Ehrlich-Schwoebel (ES) barrier along the edge of the top crystal facet triggered by lowering the supersaturation. The wedding cake model might be a general growth mechanism for flat-tipped nanowires that do not possess any dislocations. This study enriches our understanding on the fundamental kinetics of nanostructured crystal growth and provides a transformative strategy to achieve rational design and control of nanoscale geometry.