Regular Article

Surface morphology, optical and electrochemical properties of undoped and Ni-doped CeO₂ thin films prepared by polymeric precursor method

Department of Physics, Faculty of Science, University of Guilan, Namjoo av., P.O. Box 41335-1914 Rasht, Iran

^a e-mail: feghodsi@guilan.ac.ir

Received: 18 July 2015
Revised: 14 December 2015
Accepted: 21 March 2016
Published online: 20 April 2016

Abstract

In this study, undoped and Ni-doped CeO₂ thin films were deposited onto glass and ITO substrates by polymeric precursor (Pechini) method. Grazing incidence X-ray diffraction analysis revealed that the ceria thin film has a cerianite structure with the average crystallite size of 14 nm while the doped samples are amorphous. X-ray photoelectron spectroscopy (XPS) confirmed the presence of predominant Ce⁴⁺ oxidation state of ceria and Ni²⁺ in the films. Scanning electron microscopy (SEM) micrographs showed that the surface texture is crack free and the CeO₂ grains regularly distributed on the surface. Optical constant (refractive index and extinction coefficient) and thickness of films were calculated using pointwise unconstraint minimization approach. The optical transmittance increases and the absorption edge has a blue shift by Ni incorporation. The highest band gap value (i.e., 3.43 eV) was obtained for 2.5 mol.% Ni doping sample. The refractive index and extinction coefficient of ceria films were decreased by Ni doping. The evaluated thicknesses are in the range of 150–170 nm. The strength of interband transition was appraised as a function of nickel content by using dielectric function. Luminescent emission intensity of the ceria film was enhanced by Ni doping. Cyclic voltammetry (CV) measurement revealed that the total charge density and ion storage capacitance of ceria thin film were increased by Ni doping.