A spectroscopic ellipsometry study of TiO2 thin films prepared by ion-assisted electron-beam evaporation

Film characterization based on variable-angle spectroscopic ellipsometry (VASE) is desirable in order to understand physical and optical characteristics of thin films. A number of TiO2 film samples were prepared by ion-assisted electron-beam evaporation with 200-nm nominal thickness, 2.0 A/s deposition rate and 8 sccm oxygen flow rate. The samples were maintained at 250 C during the deposition, and annealed in air atmosphere afterwards. As-deposited and annealed films were analyzed by VASE, spectrophotoscopy and X-ray diffractometry. From ellipsometry modeling process, the triple-layer physical model and the Cody-Lorentz dispersion model offer the best results. The as-deposited films are inhomogeneous, with luminous transmittance and band gap of 62.37% and 2.95 eV. The 300 degrees C and 500 degrees C are transition temperatures toward anatase and rutile phases, respectively. Increasing temperature results in an increase of refractive index, transmittance percentage and band gap energy. At 500 degrees C, the highest refractive index and band gap energy are obtained at 2.62 and 3.26 eV, respectively. The developed VASE-modeling process should be able to characterize other TiO2 films, using similar physical and optical modeling considerations. (C) 2008 Elsevier B.V. All rights reserved.