Preparation and Characterization of Ta$_2$O$_5$--CeO$_2$ Films

Ta$_2$O$_5$ films have been widely studied due to their chemical and thermal stability, high dielectric constant and refractive index. It is known, for certain composites of Ta$_2$O$_5$--TiO$_2$, Ta$_2$O$_5$--Al$_2$O$_3$, and Ta$_2$O$_5$--ZrO$_2$ polycrystalline ceramics, that there is a significant increase in the dielectric constant compared to pure Ta$_2$O$_5$; this has stimulated research of doped thin films of Ta$_2$O$_5$. In this study [1], the sol-gel spin coating method has been used to make Ta$_2$O$_5$--CeO$_2$ thin films. These films have been prepared in various composition ratios to observe changes in their surface morphology, optical and structural properties. Reflectance and transmittance spectra were collected in the spectral range of 300-1000 nm, and were accurately fit using the Tauc-Lorentz model. Film thicknesses, refractive indices, absorption coefficients, and optical band gaps were extracted from the theoretical fit. The highest refractive index value was found at 5\% CeO$_2$-doping. The structure of the films was characterized by XRD and FTIR spectrometry, while the surface morphology was examined through AFM. [1] D. Saygin-Hinczewski, K. Koc, I. Sorar, M. Hinczewski, F.Z. Tepehan, and G.G. Tepehan, Sol. Energy Mater. Sol. Cells 91, 1726 (2007).