STM comparative study of the Pd8Ni92(110) alloy surface and the Pd/Ni(110)surface alloy

Both the Pd8Ni92(110) surface and a deposit of 2 monolayers (ML) of Pd/Ni(1 10) have been studied by STM, LEED, and AES in order to correlate their nan oscopic structures to their catalytic properties, which were shown to be fa r better than those of pure Pd(110). Annealing the Pd8Ni92 crystal leads to a segregation of 80% of Pd at the (110) surface layer, STM observations on Pd8Ni92 show a nanostructuring of the surface that consists of chain-like structures extending mainly parallel to, or slightly tilted along, the [001 ] direction. Extensive annealing develops a second surface phase perfectly identifiable by [001]-oriented stripes within triangular domains. Two-dimen sional alloy prepared by deposition of 2 ML of palladium on Ni(110) also ex hibits chain-like reconstruction oriented along [001] very similar to the m orphology from the alloy surface. In such structures atomic sites are close to the hexagonal arrangement of a Pd(111) surface but with a number of fau lts. These new Pd sites are supposed to be at the origin of interesting cat alytic properties. (C) 2000 Elsevier Science B.V. All rights reserved.