Surface morphology effects on Li ion diffusion toward CeO ₂ :Cu nanostructured thin films incorporated in PEG matrix

Undoped and Cu-doped CeO₂ (2.5, 5, 7.5 mol%) thin films were prepared by modified Pechini process. Grazing incidence X-ray diffraction investigations of the films revealed that the ceria thin film has a cubic structure and Cu doping inhibited the crystal growth. The presence of predominant of Ce⁴⁺ oxidation state (CeO₂) and Cu²⁺ in the films was approved by X-ray photoelectron spectroscopy. The fourier transform infrared spectra confirmed the metal-oxygen (Ce–O) bonding. Scanning electron microscopy images of the films displayed a crack free surface and the nano-grains regularly distributed on the surface. Atomic force microscopy analyses indicated that roughness parameters changed by Cu incorporation and 5 mol% Cu-doped CeO₂ is the smoothest surface. Fractal dimensions of surface were calculated by box counting and triangulation method. The fractal dimension increased by Cu doping up to 5 mol% and then reduced. The optical transmittance was enhanced and the absorption edge was shifted to lower wavelength by Cu doping. The refractive indices and extinction coefficients which were determined using theoretical approach were decreased by Cu doping. Photoluminescence emission intensity of CeO₂ thin film was quenched by Cu doping. The electrochemical behavior of the films was examined in 1 M LiClO₄/propylene carbonate electrolyte. The total charge density of ceria thin film increased by Cu doping and 5 mol% Cu-doped CeO₂ film had the highest ion storage capacitance. The fractal analyses showed that the surface morphology affected the Li ion diffusion behavior of CeO₂:Cu thin films.