Interaction of Zr with oxidized and partially reduced ceria thin films

Abstract

The growth and electronic properties of Zr on the ceria thin films were studied by X-ray photoelectron spectroscopy, low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and work function measurements. Metallic zirconium was vapor-deposited on the well-ordered fully oxidized CeO2(111) and partially reduced CeO2-x(111) (0<x<0.5) thin films, which were epitaxially grown on a Ru(0001) substrate, under ultrahigh vacuum (UHV) conditions. The results show that the deposition of Zr on both ceria surfaces leads to electron transfer from Zr to ceria, accompanied by partial reduction of Ce from Ce4+ to Ce3+ states and oxidation of metallic Zr to Zr4+. Moreover, with increasing the Zr coverage, the reduction degree of ceria films increases and eventually only Ce3+ is observed at a high coverage of Zr. The STM results suggest that Zr grows two-dimensionally (2D) on the CeO2(111) thin film at low coverages due to the strong interaction between Zr and CeO2(111).