RBS measurements of compositional change of alloys induced by ion bombardment

Abstract Ar + -bombardment induced compositional change of thin self-supporting films of NiAu alloy has been studied using the Rutherford backscattering of 2 MeV He + . It is found that the depth distribution of alloy composition both in Ni-rich and Au-rich alloys becomes uniform over the thickness of about 1000 A after a short Ar + bombardment above 400°C, and that the gold concentration continues to decrease after the composition becomes uniform. The compositional change is shown to depend on temperature only slightly between 400°C and 600°C. No overall compositional change was observed below 250°C. The result was explained in terms of a two-step segregation mechanism: the segregation from the grain to the grain boundary and from the grain boundary to the surface. According to the suggested mechanism, the overall distribution of gold is determined by the grain boundary diffusion and the persisting decrease of the overall concentration by bulk diffusion in the grains. A model numerical calculation was carried out and it is shown that the two-step segregation scheme explains the experimental results semi-quantitatively. Similar experimental results for the NiSi system are briefly described.