We have investigated the adsorption of CO and CO2 on epitaxially grown Cr2O3(111) by means of EELS. LEED, ARUPS, NEXAFS and XPS. CO is found to adsorb on the oxide surface in an ordered (√3 × √3)R30° structure with the molecular axis oriented approximately parallel to the surface. CO2 on the other hand reacts with the chromium oxide to form a surface carbonate. Adsorption of CO, respectively reaction of CO2 only takes place on a clean, freshly flashed oxide surface. Preadsorption of oxygen leads to a surface which is rather inert to adsorption, likely due to electronic or steric reasons.

Near-edge X-ray absorption spectroscopy with linearly polarized synchrotron radiation has been applied to study the orientation of the helically shaped polyaromatic hydrocarbon P-heptahelicene (C 30 H 12 ) on a Ni(100) surface under ultrahigh vacuum (UHV) conditions. By measuring the polarization dependence of the C1s f π* transitions the local adsorption geometry was determined. Between the helical axis of the molecule and the surface plane an angle of 43 ( 5°was observed for a saturated monolayer.

The adsorption of benzene on Rh(lll) was investigated by using low-energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), and angle-resolved ultraviolet photoelectron spectroscopy (ARUPS).Under very good vacuum conditions we found a (\/l9 x \/l9)R23.4°pure benzene adsorption structure which could be converted to the c(2- = -1.47 eV, indicating one of the highest benzene densities on Rh(l 11) observed so far. A considerable dispersion of the 2aig-derived band of the adsorbate layer was observed.

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X-ray absorption spectroscopy has been used to investigate the self-texture of ZnO films grown on Si(100) (lattice-mismatched substrate) by single-source chemical vapor deposition (SS-CVD) using Zn 4 O(acetate) 6 as precursor. For this system nonepitaxial growth of polycrystalline, c-axis oriented films can be controlled by addition of a water ambient during the deposition for a large variety of substrates. Angle dependent near edge X-ray absorption fine structure spectroscopy (NEXAFS) was used to study the orientation of the adsorbent molecules as a function of both water ambient used during the deposition and film thickness. The onset of self-structuring under optimum growth conditions (highest water pressure, P H 2 O ) 5 × 10 -4 mbar) is found to occur at film thicknesses on the order of 50 Å. The role of the water ambient during the film deposition is discussed using a kinetic model in which lattice stabilization due to filling of oxygen vacancies promotes the film crystallization. The model is used to explain the measured changes in the atomic environment of the oxygen atoms in the deposited ZnO films with variation in ambient water used. The interfacial restrictions in nonepitaxial CVD film growth are discussed. Our results indicate that in addition to structural restrictions due to lattice mismatch the chemical reactivity of the substrate material clearly must be considered.

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