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

Both the Pd 8 Ni 92 (110) surface and a deposit of 2 monolayers (ML) of Pd/Ni(110) have been studied by STM, LEED, and AES in order to correlate their nanoscopic structures to their catalytic properties, which were shown to be far better than those of pure Pd(110). Annealing the Pd 8 Ni 92 crystal leads to a segregation of 80% of Pd at the (110) surface layer. STM observations on Pd 8 Ni 92 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-dimensional alloy prepared by deposition of 2 ML of palladium on Ni(110) also exhibits chain-like reconstruction oriented along [001] very similar to the morphology 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 faults. These new Pd sites are supposed to be at the origin of interesting catalytic properties.