Ion sputtering of alloys

Based on an idealized model of ion sputtering of a binary alloy which consists of an easy-to-sputter and a difficult-to-sputter metal, a mass transfer calculation was carried out. Solutions for both the initial transient and subsequent steady-state concentration profiles, and the excess (sputtered) amounts of the easy-to-sputter component were obtained. For typical sputtering rates it is found that the sputtering enhanced diffusivity must be ≫10−17 cm2 s−1 before an interdiffusion zone can form. The analysis is of special significance since it shows that even when the alloy components have greatly different sputtering tendencies: (a) nonpreferential sputtering is always obtained after an induction period, the latter of which depends on the effective alloy interdiffusivity and the overall rate of sputtering and (b) the attainment of nonpreferential sputtering requires that the new surface continuously readjusts its composition in the direction of enriching in the difficult-to-sputter component. Similar results may be expected for oxides.