Abstract
The adsorption of oxygen and carbon monoxide at clean (110) faces of Cu/Ni alloys with 16, 45, 60, and 77% Ni content has been studied by means of LEED, Auger electron spectroscopy, work function measurements, and flash desorption. The results are compared with the behavior of the elementary metals. After proper preparation no phase segregation within the alloys could be detected and the surface and bulk compositions were shown to be identical by Auger spectroscopy. The adsorption of oxygen causes at first the appearance of a 2 x 1 structure on all surfaces, as is the case with Cu (110) and Ni (110). The corresponding change of the work function increases continuously with increasing Ni content. Further oxygen exposure leads to the formation of a c6 x 2 structure as on Cu (110) on a 16% Ni crystal, and to disordered adsorption at room temperature with the other samples. However, the 77% Ni surface develops a 2 x 2 structure after annealing. CO forms different ordered structures (1 x 2, 2 x 2 and c2 x 2 with the alloys. The adsorption energy of CO on the 45, 60, and 77% Ni samples is similar to that on Ni (110); the binding is somewhat weaker on the 16% Ni surface. Detailed measurements with the 60% Ni surface showed that the heat of adsorption is constant over a wide range of coverages. The results are discussed qualitatively from the point of view of the electronic structure of Cu/Ni alloys and the theory of chemisorption.
