Composition of Cu-Ni alloy surfaces

In the experimental verification of theories on surface segregation in Cu-Ni alloys, the Cu-rich side has hardly been investigated. A low-energy ion scattering study of this region is presented. Recent studies with the atom probe suggest that in Cu-rich alloys the surface segregation of Cu is much less than previously assumed. Ni would even segregate to the surface of alloys having more than 84 at.% Cu in the bulk. An explanation of these observations would require a serious revision of all existing theories. We show, however, that the clean equilibrated surfaces of the Cu-rich polycrystalline alloys consist almost entirely of Cu atoms.