Effect of post-deposition annealing on the growth of nanocrystalline TiO2 thin films and elastic anisotropy of rutile phase at different temperatures

In this work, predominant anatase and rutile nanocrystalline TiO2 thin films deposited by DC reactive magnetron sputtering are annealed at different temperatures. Raman spectroscopy and XRD experiments suggest phase transformations to rutile at elevated temperatures. A sharp increase of rutile content of the films confirms rutile phase stability above 650 °C. The variations in unit cell parameters are attributed to the changes in microstrain and macrostrain present in the films. The Miller indices dependence of Young's modulus of rutile nanocrystals is estimated on the basis of the Reuss approximation for polycrystalline aggregates. Young's modulus shows strong anisotropy. The elastic anisotropy is introduced in the Williamson-Hall (WH) method for the estimation of isotropic stress and uniform deformation energy density. Microstrain decreases with increasing annealing temperature. Lattice microstrain of nanocrystalline rutile is anisotropic. Along a particular crystallographic direction, rutile transformed from anatase rich films exhibit lower microstrain.