A combined x-ray specular reflectivity and spectroscopic ellipsometry study of CeO2/yttria-stabilized-zirconia bilayers on Si(100) substrates

The combination of x-ray specular reflectivity (XRSR) with spectroscopic ellipsometry measurements constitutes a new and useful tool for the characterization of thin films, We illustrate this statement with measurements made on CeO2/yttria-stabilized-zirconia (YSZ) bilayers deposited onto silicon substrates, CeO2 being on top of YSZ. CeO2/YSZ buffer layers are notably appropriate for the epitaxial growth of high temperature superconducting films or all sorts of oxide films on Si substrates, XRSR was used to measure the thickness of each layer of CeO2./YSZ bilayers deposited on silicon. The results showed remarkably well defined and numerous oscillations, thus revealing low interface and surface roughness. Using a modeling and fitting process with the measured data, we extracted an interface roughness between YSZ and CeO2 in the range of 0.2-0.5 nm and a CeO2 surface roughness of 1.9 nm (root mean square values). Moreover the simulation curve fitted very well if a thin amorphous SiO2 layer was assumed to lie at the interface between YSZ and Si. The optical properties of YSZ and CeO2 in the 0.25-1.7 mu m wavelength range, which are strongly dependent upon the composition and deposition parameters, were determined by the combination of spectroscopic ellipsometry measurements with XRSR results, and comparisons with the literature were made. Overall our results showed very good quality of the CeO2/YSZ oxide bilayers grown on silicon substrates. (C) 1998 American Institute of Physics. [S0021-8979(98)07421-0].