Correlation between microstructure and the optical properties of TiO2 thin films prepared on different substrates

High refractive index TiO2 thin films have been deposited by electron-beam evaporation on different substrates: Si(111) wafers, thermal SiO2, fused silica and float glass. Optical properties and growth morphology of the evaporated layers have been characterized by in situ spectroscopic ellipsometry and by transmission electron microscopy. Trajectories cos Delta = f(tan Psi) and spectroscopic ellipsometry measurements give a coherent description of film growth. The necessity of taking into account the presence of a surface layer less dense than the main part of the film is established. For thicker samples (optical thickness higher than half of the wavelength) index gradients are revealed and evaluated. The columnar structure is found in all samples, but differences in column size and-fibre packing are observed on TEM images. The influence of the nature of the substrate on the morphology and then the optical properties of the films is not well established. (C) 1997 Elsevier Science S.A.