Growth and composition of nanostructured and nanoporous cerium oxide thin films on a graphite foil

Abstract

The morphology and composition of CeO_x films prepared by r.f. magnetron sputtering on a graphite foil have been investigated mainly by using microscopy methods. This study presents the formation of nanocrystalline layers with porous structure due to the modification of a carbon support and the formation of cerium carbide crystallites as a result of the deposition process. Chemical analyses of the layers with different thicknesses performed by energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and X-ray photoelectron spectroscopy have pointed to the reduction of the cerium oxide layers. In the deposited layers, cerium was present in mixed Ce³⁺ and Ce⁴⁺ valence. Ce³⁺ species were located mainly at the graphite foil–CeO_x interface and the chemical state of cerium was gradually changing to Ce⁴⁺ going to the layer surface. It became more stoichiometric in the case of thicker layers except for the surface region, where the presence of Ce³⁺ was associated with oxygen vacancies on the surface of cerium oxide grains. The degree of cerium oxide reduction is discussed in the context of particle size.