Effect of rf power on the properties of magnetron sputtered CeO₂ thin films

Cerium oxide (CeO₂) thin films were prepared by rf magnetron sputtering (PVD) technique onto glass substrates at a pressure of 3 × 10⁻⁴ mbar of Ar⁺ atmosphere. The thickness of deposited CeO₂ films ranges from 380 to 590 nm. X-ray diffraction studies on the films showed that the films are polycrystalline in nature. The crystallite size (D), dislocation density (δ) and micro-strain (ε) were evaluated from XRD patterns. The obtained micro-strain and dislocation density of the films were found to be ~10⁻³ and ~10¹⁶ lines/m² respectively, along with a marginal increase in crystallite size from ~6 to ~9 nm. The experimental diffraction values of the films agreed with the standard values. The optical properties of cerium oxide films were studied in the wavelength range 325–900 nm. Optical absorption, extinction coefficients, refractive index and optical conductivity were evaluated from optical measurements. The films are found to be highly transparent in visible region and exhibits low reflectance in the ultraviolet region. The optical band gap of the films was found to decrease from 3.53 to 3.45 eV, with the increase of film thickness. The defects were found to increase with the increase of rf power. Emission bands like UV, weak blue, blue, blue–green and green bands were observed from PL spectra of CeO₂ thin films. Raman active mode (F_2g) of CeO₂ thin films was observed at 466 cm⁻¹ and films deposited at higher rf power show increased line width as well as peak intensity in Raman spectra. Rf power induced formations of flower like morphology were observed in SEM images. The surface roughness of CeO₂ thin films was increased from 2.9 to 7.7 nm with the increase of rf power as ascertained from AFM images and the results are discussed.