Amorphous to anatase transformation in atomic layer deposited titania thin films induced by hydrothermal treatment at 120 °C

Hydrothermal treatment has been applied successfully to convert amorphous titania films to crystalline anatase at 120 °C, a temperature compatible with most polymeric substrates. The amorphous films were deposited at 80 °C using atomic layer deposition (ALD). The crystallinity of the films was monitored by x-ray absorption near edge structure (XANES), and the film composition was determined by x-ray photoelectron spectroscopy (XPS). The effect of precursor chemistry and substrate material was investigated. It was found that titania films produced from Ti isopropoxide are easier to crystallize than those from Ti tetrachloride as the Ti precursor. The amorphous to crystalline transformation can be achieved more readily with films deposited on Si than polycarbonate substrates. The effect of a “seed” layer on the amorphous to crystalline transformation was also studied. Preformed anatase crystallites between the Si substrate and the amorphous film were shown to accelerate the crystallization process. The possible mechanisms responsible for the phase transformation are discussed.