Nucleation and growth kinetics of ZnAl2O4 spinel in crystalline ZnO – amorphous Al2O

Applying scanning electron microscopy in transmission mode and grazing incidence X-ray diffraction, we investigated the spinel-forming solid-state reaction between crystalline ZnO and amorphous Al2O3 layers prepared by atomic layer deposition. We observed two-stage phase growth of the crystalline ZnAl2O4 product layer. During the first stage, flat, pancake-like islands are formed in the nucleation process and these nuclei grow laterally without much increment in thickness. After these islands grow together to form a continuous layer, planar growth is happening in the second stage. We show that the solid-state reaction is governed by grain boundary and interface diffusion instead of interface reaction control observed between crystalline parent phases.