Project part 05 is devoted to the atomic-scale surface structures and surface processes on zirconia films, also providing a basis for the more applied studies in the other project parts. While being on the fundamental-science side of the SFB, the project part is motivated by applications in technology, with ZrO2 serving, e.g., as a support material for steam reforming catalysts, as a catalyst on its own, and as an electrolyte in solid-state electrochemistry. For ensuring adequate conductivity of the samples for scanning tunneling microscopy (STM) we will study ultrathin zirconia films created by reactive deposition of Zr and oxidation of alloys containing Zr. As a basis for further studies, also in other project parts, we will work out growth procedures for homogenous films and study their structure and defects, also trying to create defects by electron irradiation. We will work on both pure ZrO2 as well as the cubic phase stabilized by dopants (yttria, ceria). An important topic will be growth of metal/zirconia systems, by deposition of metal onto the ZrO2 surface and by partial coverage of a metal surface with ZrO2. Besides zirconia films grown in our UHV systems, we will also examine thin ALD-grown films from project part 08. The work on growth and structure will be the basis for studies of the interaction of these surfaces with simple gas molecules like O2, CO and H2, as well as atomic hydrogen. We will observe molecular species at low temperatures, adsorption of molecules at defects of the zirconia surface and, as far as possible, reactions between them. On heterogeneous (oxide+metal) systems we will focus on processes like spill-over between the metal and the oxide and diffusion on the oxide. These real-space observations should significantly improve the understanding of the surface chemistry of these surfaces and compliment spatially averaging or lower-resolution work in the other project parts. The main technique will be scanning tunneling microscopy (STM) between T = 5 K and room temperature, supplemented by the standard surface analysis methods x-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED) in this project part. The structural studies will be in close collaboration with project part 06, and especially concerning adsorption, much information will come from complementary techniques in parts 02, 03 and 04 (IRAS, TPD, molecular beam techniques, PEEM). DFT (part 11) will be indispensable for interpretation of the experimental results.