Photocatalytic properties of thin ZnO films synthesised with plasma-enhanced atomic layer deposition at room temperature

The deposition of thin active layer of zinc oxide (ZnO) on thermally sensitive substrates represents a major challenge. For this purpose, atomic layer deposition (ALD) is the most suitable deposition technique. Since both the growth rate and the quality of thin films synthesised by the conventional ALD method at temperatures near the room temperature are low, the plasma-enhanced version of the method (PEALD) is used at ambient temperatures, with which we increase the chemical reactivity of the precursors. In this work, we present the structural, optical and photocatalytic properties of thin ZnO films deposited by PEALD at room temperature. We show that the properties of the films strongly depend on the applied RF power of the plasma. The films synthesised with a plasma RF power below 200 W have an amorphous structure and a weaker photocatalytic activity. The films obtained with an RF power of 200 W or more consist of nano-sized crystallites. Compared to the amorphous films, they show significantly higher photocatalytic activity.