Electrodeposition of Oriented Cerium Oxide Films

Cerium oxide films of preferred orientation are electrodeposited under anodic conditions. A complexing ligand, acetate, was used to stabilize the cerium (III) ion in solution for deposition of the thin films. Fourier transform infrared spectroscopy showed that the ligand and metal tended to bind as a weakly bidentate complex. The crystallite size of the films was in the nanometer range as shown by Raman spectroscopy and was calculated from X-ray diffraction data. Crystallite sizes from 6 to 20？nm were obtained under the anodic deposition conditions. Sintering of the (111) oriented films showed an increase in the (111) orientation with temperatures up to 900°C. Also, the crystallite size increased from 20？nm to 120？nm under sintering conditions. Addition of the deposited films to the substrate improved corrosion resistance for the substrate. 1. Introduction The fabrication of cerium oxide films is of interest due to broad applications for these films [1–6]. Cerium oxide can function as a catalyst, structure barrier for insulator on silicon, buffer layer on superconductor materials, and an anticorrosion coating on metals [7–12]. The texture of these thin films can affect the mechanical, electronic, and corrosion properties. Electrochemical deposition is an attractive method for the synthesis of thin films. It offers the advantages of low processing temperature, high purity of deposition, and controlled thickness of the film. Cathodic electrodeposition (i.e., base generation electrochemical methods) was first introduced for the plating of cerium oxide films [13–17]. However, producing CeO2 films with the base generation method is limited since the as-produced films tend to be powdery and loosely adherent. It is possible to obtain thin films of cerium oxide by stabilizing Ce3+ in solution with a weakly bound ligand [18–20]. With a high enough oxidation potential at the electrode surface, an equilibrium can be established where Ce( )- has a slow release of Ce3+ from the complex for available oxidation. This mechanism has been described previously in greater detail [19]. These films can be electrodeposited under potentiostatic control and produce polycrystalline films of random orientation [18–21]. XANE study on electrodeposited cerium-related thin films revealed that anodic deposition preferred the Ce( ) compounds, while cathodic base generation method led to the formation of high percentage of Ce( ) species in the composition [22]. For corrosion protection, cerium oxide has been used as coatings on stainless steel. While stainless steel can give protection