MOLECULES ON OXIDE SURFACES

Metal oxides may be prepared as thin (5-50 Angstrom) films on top of m etallic substrates. By such means oxide substrates with properties ide ntical to bulk oxides may be formed which can be studied via electron spectroscopies without being hindered by charging, as well as cooling problems. We report here on results on NiO and on Cr2O3 surfaces. We d iscuss some structural aspects of oxide surfaces such as surface recon struction of polar rock salt-type surfaces, and structural phase trans itions on corundum type structures. The nature of the phase transition will be discussed with respect to the magnetic properties of the oxid e. Furthermore we report on the interaction of those surfaces with mol ecules from the gas phase. In particular we study the interaction with small molecules such as CO, NO, O-2, CO2, H2O and C2H4. We observe vi a various surface sensitive techniques such as thermal desorption spec troscopy (TDS), X-ray photoelectron spectroscopy (XPS), angle resolved photoemission (ARUPS), electron energy loss spectroscopy (HREELS), in frared-reflection-absorption-spectroscopy (IRAS), and near-edge-X-ray- absorption-fine-structure spectroscopy (NEXAFS), associative as well a s dissociative adsorption and in the case of ethylene also polymerizat ion reactions. Via isotopic labelling techniques combined with IRAS we study in detail the interaction of oxygen with the oxide surfaces, a process of general interest in connection with oxidation reactions.