On the role of Gibbsian segregation in causing preferential sputtering

It is well known that preferential sputtering with binary alloys correlates significantly with chemical binding, but only the sense and not the magnitude of the effect can be understood in these terms. It is argued here that the correlation is, in fact, an indirect one due to bombardment‐induced Gibbsian (or similar) segregation. The preferentially removed component is characterized by a composition profile consisting of a one atom‐layer‐thick spike at the surface; this is the depth from which most sputtered atoms originated so the spike must have near‐bulk composition. There is then a severely depleted subsurface region in accordance with Gibbsian segregation equilibrium (or an equivalent effect) and a final return to bulk composition. The reason for the marked correlation with chemical binding is that segregation is governed significantly more often by binding than by the alternatives of size, surface chemistry, an interstitial flux, or long‐range ordering. Copyright © 1985 Wiley Heyden Ltd.