Spectroellipsometric study of sol-gel derived potassium sodium strontium barium niobate films

Spectroscopic ellipsometry (SE) was used to characterize the sol-gel derive d (K0.5Na0.5)(0.4)(Sr0.6Ba0.4)(0.8)Nb2O6 (KNSBN) thin films as a function o f sol concentration. In the analysis of the measured SE spectra, a modified double-layer Forouhi-Bloomer model was adopted to represent the optical pr operties of the KNSBN films. In this model, the films were assumed to consi st of two layers-a bottom bulk KNSBN layer and a surface layer that compose d of bulk KNSBN as well as void. Good agreement was obtained between the me asured spectra and the model calculations in the chosen spectral region. Ef fective medium approximation theory was used to evaluate the effective refr active index for the surface layer. The results of SE have been correlated with atomic force microscopy measurements of surface roughness. Our analyse s have shown that the surface layer had a lower refractive index than the b ottom one. In addition, the refractive index and the surface roughness of t he KNSBN films increase with the sol concentration. (C) 2001 American Insti tute of Physics.