Non-fluorinated superhydrophobic and micro/nano hierarchical Al doped ZnO film: the effect of Al doping on morphological and hydrophobic properties

This work reports on the systematic comparison of the crystalline structural, morphological and hydrophobic properties of ZnO and Al-doped ZnO (AZO) thin films fabricated by atomic layer deposition and the hydrothermal method. It was revealed that the surface wettability can be largely modified by Al doping in the zinc oxide film growth process. With Al doping, the morphology of the AZO films became more complex and rough. The water contact angle of a flower-like hierarchical ZnO film (123 +/- 4 degrees) was improved by about 40 degrees via Al doping to 160 +/- 4 degrees. We attributed the variation in surface hydrophobicity with Al doping to changes in the bond angle and distance between ZnO-H2O molecule. The computational simulations have been employed to verify the interfacial distinction between two main crystal orientations of AZO. This result suggests that Al doping can be considered a critical factor in changing the surface morphology of AZO as well as the hydrophobic properties. It is believed that the present route holds promise in the design and application of practical superhydrophobic materials.