Abstract
The geometric structure of ultra-thin cerium oxide films on Rh(111), prepared by annealing the metallic cerium films at a very low coverage between 0.3 and 1.5 monolayers in an oxygen atmosphere, is investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations. The STM image and LEED pattern indicate that cerium oxide films epitaxially grown as ordered CeO2(111) layers aligned to the 110 azimuthal direction of Rh(111). The in-plane lattice parameter measured from the LEED pattern appears to be contracted with respect to the bulk ceria lattice. The measured ratio Ce:O for two-trilayer cerium oxide film is 1.96:1, which is close to the stoichiometric ratio. The simulated STM image on the basis of DFT+U calculations is in good agreement with the experimental STM images.
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