DIVERSE REACTIVITY PATTERNS OBSERVED IN THE INTERACTION OF OXYGEN WITH NICKEL DEPOSITED ON GOLD AND TUNGSTEN SURFACES

Interaction of oxygen with nickel overlayers on gold and tungsten surf aces has been investigated by employing core-level spectroscopy. The N ip(3/2) binding energy at a monolayer coverage of nickel (theta(Ni) si milar to 1 ML) is significantly different compared to that at high cov erages or of the bulk nickel, The Ni/Au surface showing a large negati ve shift in the binding energy (Delta E-c similar to -0.5 eV) adsorbs oxygen on a prolonged exposure and gives rise to a high proportion of the O1- species. In contrast the Ni/W surface with Delta E-c similar t o +0.3 eV reacts vigorously on exposure to oxygen, the O2- species bei ng predominant on the surface. Charge transfer across the Ni-Au(W) int erface is suggested to be responsible for the observed diverse reactiv ity patterns with oxygen. Bimetallic surfaces formed by depositing pal ladium on silver and tungsten surfaces also exhibit a similar behaviou r. (C) 1997 Elsevier Science B.V.