Early Stages of CeO2 Thin-film Nucleation and Growth with Photo Irradiation

In this paper, the early stages of nucleation and photoirradiation growth of CeO2 thin films have been studied. Cyclic voltammetry, chronoamperometry and scanning electron microscopy were used to analyze the nucleation process of CeO2 thin films deposited on the anode with photo irradiation. Experimental results show that the anodic deposition process with photo illumination is controlled by diffusion. Compared with the dark state, photo illumination mainly contributed to increase the current density of the three-dimensional nucleation process, because photo illumination is helpful to create active sites and accelerate the nucleation progress on the surface that a thin ceria film has been formed. Two-dimensional nucleation process mainly exists within the initial 2 s, and then only three-dimensional instantaneous nucleation process continues, which may be the main reason why the thickness of the CeO2 film can continue to grow with photo illumination but not in the dark state. Increasing the deposition overpotential can promote two-dimensional nucleation and growth rate, whilst when the potential exceeds 0.65 V, three-dimensional current density decreases. The limiting factor at that time may be the diffusion rate of cerium ions in the solution towards the electrode substrate.