Severe creep of a crystalline metallic layer induced by swift-heavy-ion irradiation

The aim of the experiments presented in this paper was to study the mechanisms leading to the atomic transport process (plastic deformation) induced in amorphous solids by GeV heavy-ion irradiation. ${\mathrm{Ni}}_3$B/Au/${\mathrm{Ni}}_3$B sandwiches, composed of a crystalline Au layer of various thicknesses and of two amorphous ${\mathrm{Ni}}_3$B layers, were irradiated at liquid nitrogen temperature with 500-MeV iodine ions. The Rutherford backscattering technique using a 3.6-MeV He beam was applied to determine the modifications of the geometry of the sandwiches due to irradiation. The results show a radiation-induced creep of the crystalline layer, with a strain-rate decreasing with increasing layer thickness. This creep phenomenon is due to the plastic deformation process occurring in the surrounding amorphous layers, and is induced by ion electronic energy loss. A simple rheological model is developed to quantify the observed effects.