A243

Surface Science 118 (1982) 1-18 1 North-Holland Publishing Company

S P E C T R O S C O P I C E L L I P S O M E T R I C I N V E S T I G A T I O N O F C L E A N

A N D O X Y G E N C O V E R E D C O P P E R S I N G L E C R Y S T A L S U R F A C E S

L.J. H A N E K A M P , W. L I S O W S K I * a n d G .A. B O O T S M A

Department of Applied Physics, Twente University of Technology, P.O. Box 217, 7500 AE Enschede, The Netherlands

Received 6 January 1982; accepted for publication 9 March 1982

Spectroscopic ellipsometric measurements (400-820 nm) have been performed on clean and oxygen covered Cu(110) and Cu(ll 1) surfaces in an AES-LEED UHV system. The complex dielectric functions of the clean surfaces were calculated from measurements between room temperature and 600 K. In contrast with Cu(lll), for the Cu(ll0) surface the ellipsometric parameters A and ~k depend on the azimuth of the plane of incidence of the light beam. Such an anisotropy was also found for the changes in A and ~/, measured upon adsorption of oxygen to coverages corresponding with approximately 1/2 and 1 monolayer. To explain the results, several models are discussed, in which changes with substrate optical properties are taken into account.

Surface Science 118 (1982) 19-31 North-Holland Publishing Company

A D S O R P T I O N K I N E T I C S F O R H Y D R O G E N A D S O R P T I O N O N

N I C K E L A N D C O A D S O R l r I ' I O N O F H Y D R O G E N A N D O X Y G E N

A. W I N K L E R a n d K . D . R E N D U L I C

Institut fi~r FestkOrperphysik, Technische Universiti~t Graz, Petersgasse 16, 8010 Graz, Austria

Received 25 January 1982; accepted for publication 7 March 1982

19

The influence of surface structure and surface impurities on adsorption kinetics has been investigated by measurements of the adsorption of hydrogen and of the coadsorption of hydrogen and oxygen on various nickel surfaces. The initial sticking coefficients for hydrogen on Ni(111), Ni(S)-[8(I 11)×(100)] and Ni(110) are found to have the values 0.05, 0.24 and 0.96, respectively. The saturation coverage of hydrogen amounts to 1.0 monolayer on Ni(l 11), 1.1 monolayers on Ni(S)-[8(I 1DX(100)] and 2.3 monolayers on Ni(110). C0adsorption supplies information about the influence of surface contamination on the sticking coefficient. In general, contamination on the surface reduces the sticking coefficient. In the special case of hydrogen adsorption on Ni(l 11) the initial sticking coefficient is increased by preadsorption of oxygen. This behavior can be described by involving a precursor state and two different types of adsorption sites on the surface. It is found that there exists a finite probability for dissociation even on occupied adsorption sites.