Mass and geometry effects on the anisotropic transport in ion mixing

Experimental investigations of the effect of target species atomic mass and system geometry on the anisotropic transport in the ion mixing of metallic systems are reported. Bilayer samples with zero heats of mixing and similar cohesive energies, but different atomic mass and geometry, such as Ta on top of Nb(Ta/Nb), Nb on top of Ta(Nb/Ta), Hf on top of Zr (Hf/Zr), and Zr on top of Hf(Zr/Hf) were irradiated by 300 keV Kr²⁺ at a dose of 2 × 10¹⁶ Kr²⁺/cm² at 77 K. The samples were investigated using embedded markers and Rutherford backscattering spectrometry. The experimental results indicate that the anisotropic transport is dominated by a preferential displacement of the top layer species into the bottom layer. This is probably due to an anisotropy in the momentum distribution within the collision cascade. In addition, there is an enhancement of the inward displacement when the lighter species is on top indicating a small preferential recoil displacement of the lighter species over the heavier one.