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O: Oberflächenphysik
O 11: Grenzfl
äche fest-flüssig
O 11.8: Talk
Monday, March 24, 2003, 16:45–17:00, M\"UL/ELCH
Formation of a passivating layer on Cu3Au(111): in-situ x-ray study — •Frank Renner1, T.-L. Lee1, S. Warren1, B.C.C. Cowie1, D.M. Kolb2, A. Stierle3, I. Costina3, B. Krause3, H. Dosch3, R. Felici4, and Jörg Zegenhagen1 — 1ESRF, Grenoble, France — 2Abt. Elektrochemie, Univ. Ulm, Germany — 3MPI-MF, Stuttgart, Germany — 4INFM/OGG, Grenoble, France
Structural details of metal surfaces play a key role for corrosion or catalytic properties. Binary metal alloys are of special interest because its properties can be tailored by the composition. Despite of keen interest, electrochemical processes on alloy surfaces on an atomic scale are little understood, mainly because of the lack of in-situ techniques. We studied Cu3Au single crystal surfaces in 0.1M H2SO4 electrolyte as a function of electrode potential in-situ by x-ray scattering. Our results show the formation of a, passivating, epitaxial Au(111) layer on the surface at a potential where Cu dissolution starts. Initially, the lattice constant of the precipitated Au islands is larger than expected, changing to the value for bulk Au only with further increasing electrode potential. The thickness of the formed islands is increasing, starting from few monolayers and growing up to several tens of nanometers. The first or second layer of the formed gold islands grows by breaking the stacking sequence of the underlying Cu3Au substrate. Crystal truncation rod (CTR) intensity profiles were recorded on a clean surface in vacuum and will be compared to profiles taken during ongoing dealloying.