CREEP OF A CRYSTALLINE METALLIC LAYER INDUCED BY HIGH-ENERGY HEAVY-ION IRRADIATION

The atomic transport induced by ion electronic energy loss in amorphou s systems is studied on metallic sandwiches irradiated at liquid nitro gen temperature with 500 MeV iodide ions delivered by the VICKSI accel erator of the Hahn-Meitner-Institut (Berlin), The sandwiches are compo sed of two amorphous Ni3B layers of 1 or 1.5 mu m thickness embedding a crystalline Au or W layer of thickness varying from 20 to 900 nm, Ru therford backscattering experiments using a 3.6 MeV He2+ beam delivere d by the ARAMIS accelerator of the CSNSM (Orsay) were performed in ord er to determine the modifications of the geometry of the sandwiches af ter swift heavy ion irradiation, The results show a huge creep of the crystalline part of the sandwiches. The magnitude of this creep depend s on the nature of the crystalline layer (Au or W) and increases stead ily with the irradiating ion fluence with a strain-rate decreasing wit h increasing layer thickness. This creep phenomenon is due to the plas tic deformation process occurring in the surrounding amorphous layers and is induced by ion electronic energy loss, A simple rheological mod el is developed to reproduce the observed effects.