Growth and structure of epitaxial Ce 1− xZr xO 2 thin films on yttria-stabilized zirconia (111)

Abstract

We describe here studies aimed at the identification of optimum parameters for the epitaxial growth of the mixed-oxide films, Ce 1− x Zr x O 2 with x=0.1, 0.2 and 0.3, by oxygen-plasma-assisted MBE on single crystal Y-stabilized ZrO 2 (YSZ) substrates. The resulting films were characterized by RHEED, LEED, XPS/XPD, XRD, and RBS/C in order to determine their bulk and surface structures and compositions. Pure-phase, epitaxial Ce 1− x Zr x O 2 films readily grew on YSZ(111) without showing any contamination of yttria from the substrate. The resulting epitaxial film surfaces are unreconstructed and exhibit the structure of bulk CeO 2(111). XPS data indicate that both Ce and Zr cations are formally in the +4 oxidation state for all films prepared here. Small differences in the photoemission results for Zr-doped ceria films as compared to those obtained for pure ZrO 2 may be explained by changes in electronic structure when Zr is added to ceria that, in turn, results from longer Zr–O bond distances in the mixed oxides. The minimum yields obtained from the random and channeling spectra of these films also provide evidence that high quality single crystal CeO 2 and Ce 0.7Zr 0.3O 2 materials were grown. For the Zr-doped films, Zr atoms are shown to occupy the lattice sites of Ce in the bulk structure of CeO 2(111). Indeed, based on minimum yield values, the fraction of Zr substitution for Ce cations in the film was estimated to be 88%.