A summary of the theory of the preferential sputtering of alloys

Preferential sputtering of alloys arises from mass differences, chemical binding differences and bombardment-induced gibbsian segregation. The relation underlying the mass effect with a binary alloy A-B is that the ratio of the sputtered fluxes scales as (MB/MA)2m where m is a number equal to 1 4 or less. A simple derivation of this scaling is given. The relation underlying the chemical binding effects is that the ratio of the sputtered fluxes scales as UB/UA where Ui is the surface binding energy. A simple derivation which relates UB/UA to nearest-neighbor binding energies is given. The relations underlying bombardment-induced gibbsian segregation take into account the fact that the steady state composition of the outermost atom layer is governed by mass and chemical binding effects but that of the second atom layer is governed by segregation such that the composition is depressed (for the component subject to segregation) by a factor K. There is no adequate theory of K but it is shown empirically that K is similar to the composition ratio observed in thermally activated gibbsian segregation. © 1985.