Photo-Controlled Wettability Switching by Conformal Coating of Nanoscale Topographies with Ultrathin Oxide Films

Here we explore the possibility of affecting the photoinduced wetting properties of nanostructures with tiny amounts of an inorganic modifier. Cicada wings are coated with a thin layer of ZnO by atomic layer deposition (ALD). We show that a few atomic layers of ZnO are sufficient to greatly modify the wetting properties. Our method only alters the surface chemistry, not the surface topography. Therefore the surface still exhibits high contact angles due to the pillars of the underlying cicada wing. At the same time, the wetting properties can be reversibly changed by UV light from nearly superhydrophobic to hydrophilic due to the ultrathin ZnO coating. We see that ALD has the potential to become a general method for modifying the photoinduced wetting properties of surfaces, keeping the topographical features of the original surface intact.