Figure 8.

Diagrams of the three postulates of the etching model: a) planar (left) and cross-sectional (right) views of a ZnO film with grain boundaries of different etch potentials, b) interaction of the etchants with the ZnO film depending on the etchant size: large (left) and small etchant (right), at grain boundaries of different etch potentials, c) resulting crater shape for large and small etchants with vertically (left) and laterally (right) limited etch rates.