Sorption of oxygen on Cu(111)-Ni surfaces and its reaction with hydrogen

Abstract

The interaction of O2 with a Cu(111)-Ni alloy and the reaction of sorbed oxygen with H2 has been investigated with ellipsometry and AES. The surface alloys were prepared by dissociation of nickel carbonyl on a clean Cu(111) surface. Sorption of O2 can be described by a precursor state model for dissociative chemisorption followed by a first order reaction of adsorbed oxygen atoms to incorporated oxygen atoms. The initial sticking probability is 10-3 at room temperature and increases with increasing crystal temperature. The first chemisorption of O2 on a freshly prepared alloy surface causes an irreversible surface reconstruction. The amount of oxygen in the near surface layer decreases with increasing crystal temperature. The reaction of sorbed oxygen with H2 can be described by a nucleation and growth mechanism with a time dependent number of growth centers. The rate is strongly affected by an operating ionisation gauge.