A I 7 0

Surface Science 28 t (1993) 83-90 North-Holland

Layer dependent core level binding energy shifts: Na, K, Rb and Cs on AI(l l l ) E. Lundgren, J.N. Andersen, M. (2~arford and R. Nyholm Department of Synchrotron Radiation Research, Institute of Physics, Lund University, SiJlvegatan 14, S-223 62 Lund, Sweden and Max-lab, Lund University, Box 118, S-221 O0 Lund, Sweden

Received 24 June 1992; accepted for publication 28 September 1992

Layer resolved core level spectra are presented for Na, K, Rb and Cs films on AI(111). From the development of the spectra, it is possible to distinguish emission from alkali atoms at the interface, in the bulk, and at the surface of the adsorbed layers. The core level binding energy shifts are discussed in terms of adhesion and interface segregation energies. It is found experimentally that the AI induced core level binding energy shifts of the alkalis are increasing with increasing atomic number of the alkali metal. This trend is qualitatively reproduced by semi-empirical calculations.

Surface Science 281 (1993) 91-101 North-Holland

Palladium alumina interface: influence of the oxide stoichiometry studied by EELS and XPS B. Ealet and E. Gillet Laboratoire de Microscopie et Diffractions Electroniques, CNRS - URA 797, Avenue Escadrille Normandie Niemen, 13397 Marseille Cedex 13, France

Received 5 May 1992; accepted for publication 2 October 1992

Electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) were used to study the initial stages of the formation of the Pd/t~-AI203(1012) interface. Two kinds of sapphire surfaces were used: (1 × 1) stoichiometric surfaces or reduced and reconstructed surfaces. Depending on the oxidation level, clean surfaces are characterized by specific electronic states located in the band gap. The evolution of the band gap structure during palladium deposition reflects the interaction meta l -a lumina which appears to be different on the two surfaces. The palladium growth process has been determined by combining Auger parameter ( a ' ) analysis with EELS measurements . It is found that reduced alumina surfaces induce a stronger electronic interaction with palladium deposit than stoichiometric surfaces do. This difference is confirmed by the Pd growth mode analysis.

Surface Science 281 (1993) 102-110 North-Holland

Surface segregation study of a dilute Pdl FeQ~ alloy by LEIS and XPS J.C. Bertolini, J.L. Rousset, P. Miegge, J. Massardier, B. Tardy, Y. Samson, B.C. Khanra 1 lnstitut de Recherches sur la Catalyse, CNRS, 2 av. Albert Einstein, 69626 l/illeurbanne Cedex, France

C. Creemers Fysico-chemisch Laboratorium, Katholieke Universiteit Leuven, Celestijnenlaan 200G, B-3001 Leuven, 13elgium

Received 30 July 1992; accepted for publication 9 October 1992

Pd segregates to a large extent to the surface of a PdlFe99 alloy stabilized at 870 K. The outer layer composition contains as much as 55 _+ 5 at% Pd as deduced from LEIS data. Complementary XPS measurements performed at various exit angles with respect to the surface indicated that the Pd enrichment extends to more than one layer below the very surface. A calculation of the segregation free enthalpy based on the broken bond model using macroscopic thermodynamic data, allows us to describe the concentration equilibrium between the first and second layers well.