The CeO2-x particles can be reversibly oxidized and reduced, due to switching between Ce4+ and Ce3+ oxidation
states coupled to the possibility to absorb and release oxygen [6]. Investigations by high resolution transmission
electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have already been performed on ceria
systems [7-9] but mainly for ceria nanopowders [10-17] and not for thin films. The combination of the two
techniques allows the correlation of spectroscopic information with detailed structural knowledge of a material [15-
17]. The Ce4+ M4,5 edge shape, intensity, and energy differ from those of Ce3+. Therefore, changes in edge shape,
peaks position and peaks area give information about the valence of Ce atoms.
Previous studies of thin films deposited using radio frequency magnetron sputtering on silicon substrate have
shown that the surface layer is relatively flat in contrast with porous structure obtained with an intermediate carbon
layer [18-20]. Moreover, hard X-ray photoelectron spectroscopy (HAXPES) experiments have revealed the partial
reduction of cerium and the formation of complex cerium silicates at the interface [21]. However, no structural study
combined with a complete investigation by EELS was performed yet.
In this study, we report TEM investigations carried out on CeO2 layers deposited on a Si substrate by Radio
Frequency (RF) magnetron sputtering. Before the study of Pt-doped ceria thin films grown on silicon substrate
interesting for fuel cells applications [22], this study aims at characterization of undoped ceria thin films to obtain
references before studying the effect of Pt co-deposition. Coating morphology observations, crystallographic
structures determination, elemental chemical analyses and cerium oxidation states determination by EELS
measurements have been performed.