title: Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory.
abstract: Ultrathin (∼3 Å) zirconium oxide films were grown on a single-crystalline Pt3Zr(0001) substrate by oxidation in 1 × 10-7mbar of O2at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO2films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO2films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O-Zr-O) films on the alloy; only a small area fraction (10-15%) is covered by ZrO2clusters (thickness ∼0.5-10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO2films are between those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core level shifts to substoichiometric ZrOxis not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO2films or metal/ZrO2interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators.
authors: Institute of Materials Chemistry, Vienna University of Technology , 1060 Vienna, Austria.
authors: Hao
authors: H
authors: Li
authors: Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria.
authors: Joong-Il Jake
authors: JI
authors: Choi
authors: Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria ; Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria.
authors: Wernfried
authors: W
authors: Mayr-Schmölzer
authors: Institute of Materials Chemistry, Vienna University of Technology , 1060 Vienna, Austria.
authors: Christian
authors: C
authors: Weilach
authors: Institute of Materials Chemistry, Vienna University of Technology , 1060 Vienna, Austria.
authors: Christoph
authors: C
authors: Rameshan
authors: Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria ; Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria.
authors: Florian
authors: F
authors: Mittendorfer
authors: Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria ; Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria.
authors: Josef
authors: J
authors: Redinger
authors: Institute of Applied Physics and Center for Computational Materials Science, Vienna University of Technology , 1040 Vienna, Austria.
authors: Michael
authors: M
authors: Schmid
authors: Institute of Materials Chemistry, Vienna University of Technology , 1060 Vienna, Austria.
authors: Günther
authors: G
authors: Rupprechter