By using STM, LEED and ISS we have studied the condensation of Pt on clean NiAl(110) and on a thin ordered Al2O3 film grown on NiAl(110). On Al2O3NiAl(110) and up to a coverage of one monolayer Pt forms highly dispersed two-dimensional islands with an average diameter of 10–30 Å whose density increases with the coverage. For higher Pt coverage the formation of three-dimensional Pt clusters is observed. Annealing of the Pt-covered surface leads to a diffusion of Pt into the oxide film. On clean NiAl(110) and up to one monolayer we found two-dimensional growth of Pt the density of the islands remaining approximately constant.

In contrast to metal surfaces, oxide surfaces have only been studied rather recently with surface science methods. We report on the preparation and electron spectroscopic investigations of thin, well ordered surfaces of clean, adsorbate covered and modified oxide films. We identify surface excited states of a NiO(100) surface via electron energy loss spectroscopy in the regime of electronic excitations. Adsorption on well ordered terraces and on defects can be distinguished by choosing proper probe molecules. As a model system to study the structure and reactivity of an oxide supported ultrathin metal film we have deposited Pt onto a thin A1203(111) film grown on a NiAI(110) substrate. CO adsorption and low temperature dissociation in contrast to the bulk Pt has been observed.

Via oxidation a well ordered Al2O3 film may be grown on an ordered NiAl(110) surface. Its structure has been studied with SPA-LEED (spot-profile analysis) as well as with scanning tunneling microscopy (STM). The oxide overlayer grows strictly two-dimensional with a thickness of close to 5 Angstrom. Double diffraction spots have been observed but they are very weak, thus not excluding the existence of an interfacial layer between NiAl(110) and the oxide film. STM provides preliminary evidence for such a film and presents first clues to what the structure of the interface may be.The defect structure of the Al2O3 film has been investigated. In addition to boundaries between two rotational domains constituting the Al2O3 film, we also identify anti-phase domain boundaries through both the SPA-LEED as well as the STM measurements.

We have investigated the electronic and geometric structure of surfaces of transition metal oxides and simple metal oxides applying electron spectroscopic methods. In order to avoid charging problems, we have resorted to the preparation of thin (5 – 50 Å) metal oxide films grown on metallic substrates via several oxidation techniques. We have studied NiO, CoO, Cr2O3, and Al2O3. The thin films have the advantage that they may be easily cooled to liquid nitrogen and liquid helium temperatures. Another interesting feature of the thin films is the possibility to prepare thermodynamically unstable surfaces, such as (111) surfaces of ionic rock salt structures, and study the adsorption and reaction at such surfaces. Adsorption and reaction of molecules has not only been investigated on the clean oxide substrates but also on the surfaces modified through deposited ultrathin metal films. Such systems may be considered as models for heterogeneous catalysts.

Molecular adsorption on oxide surfaces is gaining increasing interest both experimentally and theoretically. Adsorption studies on model systems, where well ordered thin oxide films grown on a metal substrate to avoid sample charging in connection with electron spectroscopic measurements, were used, are reported. Two oxide systems are compared: (i) a reactive transition metal oxide surface of Cr2O3(111) where it is shown that the surface contains Cr2+ ions which trigger its reactivity; (ii) a non-reactive simple metal oxide surface of γ-Al2O3(111) which is used as a support model surface. The adsorption of various molecules on both surfaces has been examined, and how the properties of the surface are modified when metals are deposited on the oxide surface have been studied. The results of alkali metal deposits on Cr2O3(111) and Pt deposits on γ-Al2O3(111) are presented. The applied methods include LEED, STM, TPD, ARUPS, ELS, XPS, HREELS and ISS.