Ion irradiation induced impurity redistribution in Pt/C multilayers

Ion irradiation induced modifications of a periodic Pt/C multilayer system containing Fe impurity have been analyzed by X-ray techniques suitable for exploring nanometer depth scales with sub-nanometer depth resolution. The multilayer stack with 15 Pt/C layer pairs (period 4.23 nm, total thickness 63.45 nm) was fabricated on a glass substrate. A 2 MeV Au2+ ion beam was rastered on the sample to obtain uniformly irradiated strips with fluences from 1 x 1014 to 1 x 1015 ions/cm2. These strips were analyzed with X-ray standing wave and X-ray reflectivity experiments. Ion induced atomic displacements across multilayer interfaces are known [Appl. Phys. Lett. 79 (2001) 467]. Here additionally we identify irradiation induced redistribution of Fe impurity atoms, which cannot be explained simply by atomic displacements due to ion-atom collision. With increasing ion fluences more Fe atoms migrate from C- to Pt-layers. This behaviour has been explained in terms of radiation induced enhanced diffusion and Fe-Pt and Fe-C phase diagrams