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J. Choi:
"Studies of Zirconia Surfaces on the Atomic Scale";
Betreuer/in(nen), Begutachter/in(nen): M. Schmid, A. Stierle; Institut für Angewandte Physik (E134), 2016; Rigorosum: 22.04.2016.

ZrO2 finds a wide range of applications due to its favorable properties including electronic insulation (band gap Eg ≥ 5 eV) and oxygen ion conductivity when doped. In this thesis I present atomic-scale studies on the structure of ultrathin zirconia films followed by adsorption and deposition studies on the oxide and the growth of thicker oxide layers, by means of STM (Scanning Tunneling Microscopy), XPS (X-ray Photoelectron Spectroscopy), AES (Auger Electron Spectroscopy) and LEED (Low-Energy Electron Diffraction).
Ultrathin zirconia films were prepared by oxidation of Zr-based alloys (Pt3Zr and Pd3Zr), which results in the growth of a trilayer (O-Zr-O) zirconia film equivalent to the (111) surface of cubic ZrO2. Depending on the preparation conditions and the substrate (Pt3Zr or Pd3Zr) the amount of distortion in the oxide changes, mainly caused by different bonding mechanisms of the oxide film to the substrate, which can be via Zrox-Ptsub (ZrO2/Pt3Zr) or Oox-Zrsub (ZrO2/Pd3Zr) bonds.
Adsorption of water is unexpectedly strong (Eads(exp)=1.08-1.10 eV on ZrO2/Pt3Zr); surface hydroxyl groups are bound even more strongly. Metal nanoclusters (Ag, Au, Pd, Ni and Fe) also show the strong interaction with the ultrathin zirconia films (Wadh = 1.3 J/m2 for Ag on ZrO2/Pt3Zr). This can be attributed to the good accessibility to the metal cations due to a wide O-O distance of the oxides (≈ 350 pm) compared to other oxygen-terminated oxides.
Multi-layer zirconia films were grown on Pt(111) and Rh(111) by sputter deposition of zirconium. Zirconia dewets the substrate upon annealing. In between the zirconia islands, we find the trilayer oxide films when annealed in UHV, but this film disappears when annealed in oxygen, an effect known as strong metal-support interaction (SMSI).