AVS 46th International Symposium
    Surface Science Division Monday Sessions
       Session SS3-MoM

Paper SS3-MoM3
Water Adsorption Structures on Flat and Stepped Ru(0001)-Surfaces

Monday, October 25, 1999, 9:00 am, Room 612

Session: Water-Surface Interactions
Presenter: C. Benndorf, University of Hamburg, Germany
Authors: W. Hoffmann, University of Hamburg, Germany
C. Benndorf, University of Hamburg, Germany
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We investigated the structural influence of vicinal Ru(0001) surfaces to water adsorption and desorption kinetics. Flat Ru(0001) surfaces show a unique behavior in the difference of H@sub2@O and D@sub2@O desorption spectra - referred to as the isotope effect. In accordance with other authors we observed on Ru(0001) three desorption peaks for H@sub2@O denoted as C, A@sub2@ and A@sub1@ (C, 155 K / A@sub2@, 190 K / A@sub1@, 212 K).The isotope effect for D@sub2@O on Ru(0001) is characterized by a missing A@sub1@ peak. Isothermal desorption measurements were performed using @Delta@@phi@, in order to determine the different kinetics for H@sub2@O and D@sub2@O. Neither for D@sub2@O nor for H@sub2@O the desorption of the A@sub2@-state can be described by 1st order kinetics. Especially for the A@sub2@ peak of H@sub2@O we observed an initial range of 1st order kinetics followed by a strong deviation, which could be described by Avrami kinetics or lateral interactions.@footnote 1@ Stepped Ru surfaces were used for comparison and @Delta@@phi@ measurements were complemented by ARUPS measurements of H@sub2@O and D@sub2@O adsorption. Further we performed LEED structure calculations of the clean stepped hcp(0001)-surfaces using a spherical wave model approach and single scattering theory.@footnote 2@ In experiments the vicinal Ru(0001) surfaces show a triplet spot splitting due to the alternating step width with different atomic arrangements at the steps, in agreement with our calculations. Regarding the adsorption phenomena on low indexed stepped surfaces, the diffraction pattern do not show ordered structures of water molecules. Higher indexed surfaces allow to built ordered water super structures as observed for flat Ru(0001) surfaces.@footnote 3@ @FootnoteText@ @footnote 1@ W. Hoffmann, C. Benndorf, Surface Sci. 377-379 (1997) 681-686. @footnote 2@ W.P. Ellis and R.L. Schwoebel, Surface Sci. 11 (1968) 82-98. @footnote 3@ D. L. Doering and T. E. Madey, Surface Sci. 123 (1982) 305-337.