Giant deformation of solids irradiated with swift heavy ions: Behavior of amorphous/crystalline multilayers

A peculiar manifestation of particle-solid interaction is the plastic deformation of amorphous materials irradiated with a beam of swift heavy ions. This paper presents a study of this process on samples composed of a crystalline metallic layer sandwiched between two amorphous layers. The RBS technique is used to determine the modifications of the geometry of the multilayers due to irradiation. The results show a huge shrinkage along the beam direction of both the amorphous and crystalline layers, with a decreasing deformation rate when the amorphous/crystalline layer thickness ratio decreases. The deformation is ascribed to the strong electronic excitation generated in the wake of the incident ions. The amorphous parts of the target experience the plastic deformation phenomenon observed previously, while the crystalline layer is subject to a severe creep driven by the expanding adjacent amorphous layers. The analysis of the results with a rheological model provides an estimate of the maximum compressive stress which stops the plastic deformation in amorphous solids.