Relations between the optical properties and the microstructure of TiO2 thin films prepared by ion-assisted deposition

Oxygen ion-assisted TiO2 thin films have been studied by il I situ visible spectroscopic ellipsometry (SE) and transmission electron microscopy (TEM). Influence of the substrate nature and the substrate temperature, the ion kinetic energy E-c and the ion/molecule ratio Phi(i)/Phi(at) was investigated on the microstructure and the optical properties of the films. It is revealed that the refractive index n varies as a function of the average energy per TiO2 molecule, E-d = E-c(Phi(i)/Phi(at)). Conditions for obtaining dense films with a high refractive index (n similar to 2.60 at lambda = 0.45 mu m) and a low extinction coefficient k have been found for E-d > E-dth (E(dth)similar to 50 eV). These dense films are insensitive to moisture adsorption with a low surface roughness. Cross-sectional TEM has been mainly used for microstructure observation and phase identification of the films prepared under different evaporation conditions. Comparison is done in relationship with the optical property measurements. (C) 2000 Elsevier Science S.A. All rights reserved.