Growth and dissolution kinetics of Au/Pb(111):: an AES-LEED study

The growth of An on a Pb(I 1 1) surface is studied by AES-LEED at room temperature (RT). After deposition of 1/3 Au monolayer (ML), LEED observations reveal a p(,root3 x root3)R30degrees superstructure. Beyond this coverage, no superstructure is observed. From An and Pb Auger peak intensities, we deduce that the growth corresponds to the formation of an inter-metallic compound AuxPby continuously growing under a floating Pb ML. The dissolution kinetics of one An ML recorded at various temperatures systematically show a plateau (a slowing down) at a surface concentration corresponding to 1/3 NIL. From a quantitative evaluation of the AES data we propose that the p(root3 x root3)R30degrees superstructure corresponds to a surface alloy with composition AuPb2 buried under I Ph ML. Such a surface alloy has been previously measured after annealing of a Au(Pb) 0.45 at.% solid solution [Surf. Rev. Lett. 4 (1997) 1139], we propose that the slowing down observed during the dissolution kinetics is also the signature of this unexpected segregation behaviour of An. It could be related to the fact that the surface energy of this inter-metallic compound (AuPb2) is lower than the surface energy of both constitutive elements (An and Pb). (C) 2003 Elsevier Science B.V. All rights reserved.