Ultraviolet light-induced wettability control of ultrathin atomic layer deposited TiO2 film surface

Here, we show that the surface wettability of ultrathin (6-16 nm) TiO2 films deposited by atomic layer deposition (ALD) can be tuned by an ultraviolet (UV) light treatment. The controllability is also shown to be largely dependent on the deposition temperature and thickness. The surface of a 16-nm-thick ALD TiO2 film deposited at 200 °C was shown to be super-hydrophilic (water contact angle < 1°) by an UV treatment (~ 3 mW/cm2) applied for only 8 min due to the photocatalytic activity of the films, while thinner films and films deposited at lower temperatures were not. Microscopic and optical characterizations prove that the difference mainly stems from the crystallinity, the bandgap energy and the defect density of the TiO2 films.