Study On The Fabrication And Characterization And The Related Behavior Of Nanostructured CeO₂ Films

Nanostructured CeO2 thin films with fluorite structure not only retain the unique 4f electronic shell and single crystal of rare earth elements, but also contain surface effect, quantum size effect, small size effect, macroscopic quantum tunneling effect and other characteristics of nano-materials. Thus they have many properties different from those of traditional materials, such as excellent O2 storage and release function, redox ability, good high-temperature ionic conductivity, excellent self-healing and so on. In catalysis, fuel cells, protective metal coatings and other areas, nanostructured CeO2 films have wide application prospects.On the basis of extensive investigation of literatures at home and abroad on the preparation methods of nanostructured CeO2 thin films, this paper has mainly undertaken the following four aspects:(1) The influences of principle technological parameters(including the type of acid cation ligands, ligand concentration and O2) on the microstructure of anodic electrodeposited CeO2 films were investigated in this thesis, and finally we obtain a stable reliable optimized process of anodic electrodeposition nanostructured CeO2 thin films. The results show that the ligand of ammonium(NH4+) in CH3COONH4 plays an important role in grain refinement of CeO2thin films. High concentration of CH3COONH4 ligand and oxygenation effects to electroplating solution are in favor of densification of CeO2 nano-particles.(2) Nanostructured CeO2 thin films prepared under optimal conditions are characterized by series of modern materials measurement technology, such as SEM, XRD, spectroscopic ellipsometry and so on. The results show that optimized nanostructured CeO2 thin films have a substantial nanostructure, and its average grain size is about 5-10 nm, and the thickness of film is about 17 nm. (3) We have produced nanostructured CeO2 by cathodic electrodeposition with a constant current density and sol-gel process. CeO2 nano-particles prepared by cathodic electrodeposition are adhesive to substrate, homogeneous, and directional growth; but CeO2 nano-particles prepared by sol-gel process are weakly adherent to the substrate and powdery and exhibit a random orientation.(4) The mechanism of anodic electrodeposition CeO2 thin films is preliminary studied by Cyclic Voltammetry(CV). The study shows that the deposition process of nano-CeO2 follow the "indirect electro-oxidation forming mechanism". That is Ce3+ ions in solution with dissolved oxygen are generated to CeO2 powder or crack CeO2 films under the influence of O2 molecules.