ATOMIC POSITIONS OF AU ATOMS ON A NI(110) SURFACE

The arrangement of Au atoms segregated to the (110) surface of a Ni-0. 8at%Au alloy was studied with low energy ion scattering (LEIS) in comb ination with low energy electron diffraction (LEED). The results of th e LEED analysis have been published earlier [1]. From this analysis it is known that at the very low coverage of around 0.1 monolayer (ML) a 1 X 1 symmetry exists. At high coverages (approximately 1 ML) a 7 X 7 overlayer structure with c(2 X 4) subunits was observed. At intermedi ate coverages also other symmetries were observed such as (5 X 1) and c(2 X 2). By comparing angular LEIS scans with the results of computer simulations, we were able to determine part of the Au configurations giving rise to these observed symmetries. At low coverage the Au atoms were found to occupy near-substitutional sites in the Ni top layer. N o Au atoms were observed on top of the Ni surface, nor in the second N i layer. The 7 X 7 reconstructed surface is formed by a hexagonal, inc ommensurate, Au overlayer on top of the Ni (110) structure. A complete 7 X 7 structure would give rise to a coverage of 1.28 ML of Au atoms.