Evidence for atomic mixing induced in metallic bilayers by electronic energy deposition

High levels of energy deposition by electronic excitations can induce damage creation in some bulk metallic targets as soon as the rate of energy deposition in electronic excitation is higher than a few 10 keV/nm. The present study is aimed at determining whether such excitations can also induce interdiffusion at the interface of metallic bilayers. Ni/Ti bilayers were irradiated at 80 K with GeV Pb, Ta and U ions up to a few 10¹³ ions/cm². Damage creation and mixing were followed using various methods: electrical resistance, grazing X-ray and neutron reflectometry, X-ray diffraction, electron microscopy and electron energy loss on target cross-sections. A very strong mixing is indeed observed at the Ni/Ti interface as a result of electronic energy deposition: the observed mixing efficiency is at least two orders of magnitude higher than that induced by elastic collisions with target nuclei. We finally study the influence of various parameters (irradiation temperature, symetry of the interface) on the mixing efficiency and follow the kinetics of the mixing process.