Subsurface compositional modification of Au-Cu alloys sputtered with Ar, Xe, Ne and Kr ions

Surface and subsurface compositional changes in Au-Cu alloys and thin films sputtered with 2 keV Ar, Xe, Ne and Kr ions were observed with low energy (60 eV for Cu and 69 eV for Au) and high energy (239 eV for Au and 920 eV for Cu) Auger peaks at temperatures between liquid nitrogen and room temperature. For a Au_0.56Cu_0.44 alloy, Au enrichment at the surface and depletion beneath the surface was observed with high energy as well as low energy Auger peaks. But the compositional change assessed with low energy Auger peaks is greater than that assessed with high energy peaks. This was also calculated with the simulation of sputtering including ion radiation-enhanced segregation and diffusion. This shows clearly that the Gibbsian segregation plays an important role in composition changes at the surface and subsurface of the ion-sputtered alloy. Compositional changes of Au-Cu thin film alloys prepared by the co-evaporation technique were also observed following sputtering with Ar, Xe, Ne and Kr. Except in the case of Xe, the coevaporated composition was preserved during sputtering at low temperatures (<-120°C).