Energy dependence of the surface composition changes in AuCu alloys under Ar + ion bombardment

Abstract

The energy dependence of the surface composition changes in AuCu alloys under Ar + ion bombardment has been studied. When the energy of the Ar + ions is higherthan 1 keV, the surface concentration of gold decreases with bombardment time gradually approaching the steady state value, which is somewhat lower than the bulk concentration of gold. Depth profiling indicates that gold is enriched at the outmost layer with a gold-depleted zone beneath it. When the energy of the Ar + ions is lower than 1 keV, however, the surface concentration of gold increases with time reaching a maximum, then decreases toward a steady state value, which is higher than the value of the bulk. Depth profiling indicates that gold is enriched not only at the outmost layer but also in the subsurface region. Bombardment with Ar + ions of 1 keV energy gives steady state concentration of gold, which is close to the bulk value. From these results, some possible explanation of the difference between the present observation and an early result obtained by Gillam are discussed. These results can be regarded as new evidences to support a new point of view on preferential sputtering of binary alloys. This suggests that the so-called preferential sputtering in most binary alloys may be identical to the bombardment-induced Gibbsian segregation, but when ion energy decreases toward a near-threshold condition, the mass-correlating preferential sputtering also play a role.