Differential Etching of ZnO Native Planes under Basic Conditions

Abstract

The in situ dissolution of polished (0001), (101(-)0), and (0001(-)) surfaces of ZnO was studied using Atomic Force Microscopy under alkaline conditions. In aqueous NaOH solution the (0001) plane forms a stepped surface whereas the (0001(-)) plane converts into more stable {101(-)1(-)} planes. Dissolution of the (101(-)0) plane leaves a combination of (0001) and (101(-)1(-)) planes. Dissolution in solutions containing both NaOH and Na(3)citrate causes the (0001) plane steps to increase in number and reduce in height, and cause an overall increase in the rate of dissolution in the [101(-)0] directions. These observations are explained using a mechanism based on edgewise dissolution where the etching rate depends on the number of surface oxygen atoms per zinc atom. Large areas of single index faces (over 50 μm(2)) of (0001) and (0001(-)), suitable for surface chemistry studies, were also generated by chemical dissolution.