Relationship between the Nanostructures and the Optical Properties of CeO₂ Thin Films

Abstract

CeO 2 nanostructured thin films have been deposited on Al 2 O 3 (1-102) and TiO 2 (001) single-crystal substrates through metal-organic chemical vapor deposition (MOCVD) using the Ce(III) 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato diglyme adduct (Ce(hfa) 3 ‚diglyme). Structural and morphological characterizations have been carried out by X-ray diffraction pattern (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) measurements. It has been found that the deposition temperature and the lattice mismatch with the substrate have a strong impact on the film nanostructure. X-ray diffraction patterns of samples grown at low deposition temperature point to the formation of 〈100〉 oriented CeO 2 films, while films deposited at higher deposition temperatures have 〈111〉 texture. Furthermore, SEM cross section images clearly point to relevant effects of deposition temperatures both on the structural alignment of CeO 2 grains as well as on the film/substrate interfaces. Spectroscopic ellipsometric measurements provide a suitable rationalization of correlations between nanostructures and optical properties of the CeO 2 films. Moreover, combination of SEM and spectroscopic ellipsometric measurements provide an in-depth interpretation of growth modes.

Electrodeposition of nanometer-thick ceria films by oxidation of cerium(III)–acetate

“…Numerous methods exist for the deposition of ceria films, including sputtering [24], e-beam evaporation [25], chemical vapor deposition [26], and sol-gel processing [27]. However, the low cost and low processing temperatures (near room temperature) of electrodeposition make it an especially appealing means to deposit thin ceria films.…”

Construction of Indium and Cerium Codoped Ordered Mesoporous TiO2 Aerogel Composite Material and Its High Photocatalytic Activity

“…Under the protonation, the superoxide anion radicals (O 2 • − ) generates the hydroperoxyl radicals (HO 2 •) which subsequently produces hydroxyl radicals (•OH). In terms of cerium doping, the relative mobility of oxygen on the surface of TiO 2 is much higher . The VB of TiO 2 also has a potential of +2.9 eV, which is more positive than the oxidation potential of Ce 3+ to Ce 4+ (−1.61 eV).…”

“…CeO 2 is one of the most active rare earth metal oxides with a band gap of 2.92 eV. It has a high optical transparency in visible region, and possesses a high capacity to store oxygen . CeO 2 can be used for photocatalytic degradation of organic pollutants in wastewater .…”

High-speed epitaxial growth of (100)-oriented CeO2 film on r-cut sapphire by laser chemical vapor deposition

“…However, the R dep was almost the same to T dep and the apparent activation energy of the film growth was almost zero, implying that the rate-limiting step was mass transportation in a gas phase due to enhancement of surface chemical reaction by laser irradiation. Table 1 shows a comparison of the R dep , crystallinity, in-plane orientation and morphology of the CeO 2 films prepared on Al 2 O 3 substrate by plasma-enhanced halide CVD [20], MOCVD [1,[26][27][28] and the present laser CVD. In conventional CVD, the crystallinity of the CeO 2 films was closely related to their R dep (b0.1 μm h − 1 ) and the increase in R dep usually deteriorated the crystallinity of a film [1,20,[26][27][28] because the epitaxial growth took place under a significantly low supersaturation level and a low R dep [9,29].…”