Derivation of the optical constants of spin coated CeO 2–TiO 2–ZrO 2 thin films prepared by sol–gel route

Abstract

Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol–gel process and deposited by a spin coating technique at different spin speeds (1000–4000 rpm). Ceric ammonium nitrate, Ce(NO 3) 6(NH 4) 2, titanium butoxide, Ti[O(CH 2) 3CH 3] 4, and zirconium propoxide, Zr(OCH 2CH 2CH 3) 4, were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO 2–TiO 2–ZrO 2 gel to study the decomposition and phase transition of the gel. For molecular, structural, elemental, and morphological characterization of the films, Fourier Transform Infrared (FTIR) spectral analysis, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), cross-sectional scanning electron microscopy (SEM), and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index, extinction coefficient, band gap) and thickness of the films were determined in the 350–1000 nm wavelength range by using an nkd spectrophotometer. The refractive index, extinction coefficient, and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple–DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E g ≈2.82±0.04 eV for indirect transition.