Growth and structure of epitaxial Ce0.8Sm0.2O1.9 by oxygen-plasma-assisted molecular beam epitaxy

We used oxygen-plasma-assisted molecular beam epitaxy (OPA-MBE) to grow highly oriented Ce0.8Sm0.2O1.9 films on single-crystal c-Al2O3. Films were characterized by X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The film/substrate epitaxial relationship can be written as CeO2(1 1 1)//α-Al2O3(0 0 0 1) and CeO2[1 1 0]//α-Al2O3[2¯110]. Ce and Sm were found to be in their highest oxidation state, +4 and +3, respectively. The doped cubic CeO2 films have a preferred (1 1 1) orientation. Significant conductivity difference was observed between single and polycrystalline films. A good orientation existing in the single-crystalline thin films may help long-range oxygen vacancy transport, ultimately contributing to significantly higher conductivities, in comparison to polycrystalline films.