Scaling coefficient for three-dimensional grain coalescence of ZnO on Si(111)

Grain-rotation-induced coalescence is a well-known growth mechanism of granular/polycrystalline systems in two dimensions. In three-dimensional (3D) crystals there are more degrees of freedom, and influences of the substrate play an important role. In the present work we analyze the 3D coalescence of ZnO grains on Si(111) by thermal annealing under O-2 atmosphere. Atomic force microscopy and electron backscatter diffraction measurements reveal a significant increase in the mean grain diameter and a reorientation that matches the substrate orientation. This structural reorganization leads to a substantial enhancement of the electronic layer quality. We describe the grain growth with a diffusive model and find a volume scaling coefficient of 1.5. This proves that the additional degrees of freedom significantly accelerate grain-rotation induced coalescence in three dimensions. DOI: 10.1103/PhysRevB.86.224108