Photoelectrochemical Etching on Zinc Oxide Single Crystals: Crystallographic Surface Dependence and Wettability Control

Abstract

Photoelectrochemical etching was applied to (0001), (000-1), and (10-10) surfaces of ZnO single crystals to produce unique surface structures, which depend on the crystallographic face. These surfaces turned hydrophilic with a water contact angle of 5–10° under ultraviolet light irradiation, but the hydrophilicity gradually became small in the dark. Among them, we successfully generated a hydrophobic surface (contact angle >120°) stored in a dark under ambient conditions on the etched (000-1) face with hexagonal holes that had a diameter of approximately 100 nm along the c-axis. In addition, storing at 75°C in a dry oven greatly shortened the period of the hydrophobic conversion.