Microstructure and elastic properties of atomic layer deposited TiO2 anatase thin films

Amorphous TiO2 thin films were deposited by means of atomic layer deposition on Kapton substrates and then crystallized ex situ by annealing at 300 °C to obtain the anatase phase. The morphology, structure and microstructure of films treated for 12, 24, 72 and 90 h were investigated. The local Ti coordination changes were studied by X-ray near-edge structure (XANES).On the basis of X-ray diffraction residual stress calculations, the elastic anisotropy of the films is experimentally determined for the first time (Acomp∗=0.07, Ashear∗=0.03). The film macro-strains increased with the time of treatment, while the micro-strains decreased. This effect may be correlated with the incipient anatase-to-rutile transformation as suggested by the changes observed in the XANES pattern of the film treated for 90 h. However, the contribution of the substrate cannot be excluded.