Epitaxial growth and structure of monolayer cerium oxide films on Rh(111)

Abstract

We prepared monolayer cerium (Ce) oxide films on Rh(111) to investigate their growth and structure using scanning tunneling microscopy (STM), low-energy electron diffraction, X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations. For quantitative analysis of Ce-oxide films, we used the combined techniques of XPS and Rutherford backscattering spectrometry to determine the concentration of Ce and O atoms. We prepared a monolayer (ML) Ce-oxide film by annealing a metallic Ce film at 0.3ML coverage in an oxygen atmosphere. A well-ordered Ce-oxide phase with a (4×4) unit cell was obtained. The epitaxially grown Ce-oxide film aligned along the 〈110〉 azimuthal direction of Rh(111). The number of Ce and O atoms in the (4×4) unit cell was estimated. The STM images indicated that the two-dimensional island growth of the p(4×4) phase with p3m1 symmetry can be explained using the missing Ce atoms model. A simulated STM image of the p(4×4) structural model was in good agreement with the experimental STM image. The formation of Ce-oxide films on Rh(111) at submonolayer coverage was discussed on the basis of the results of DFT+U calculations.