Spectroellipsometric characterization of materials for multilayer coatings

The optical functions of titanium dioxide (TiO2). tantalum pentoxide (Ta2O5 ) and silicon dioxide (SiO2) have been determined in the spectral range fro m 1.5 to 5.4 eV (wavelength range from 230 to 840 nm). The ellipsometric sp ectra of 200 nm thick layers sputtered on a glass substrate were measured b y a four-zone null spectroscopic ellipsometer. The data have been fitted by a Tauc-Lorentz model recently derived by Jellison and Modine for the optic al functions of amorphous materials. The model dielectric function is based on a combination of the Tauc band edge and the Lorentz oscillator. The eff ects of the surface and interface layers and layer inhomogeneity on the mea sured data are discussed. (C) 2001 Elsevier Science B.V. All rights reserve d.