Ion-beam irradiation can be used as a processing tool to synthesize
metastable materials. A particular case is the preparation of solid
solutions from immiscible alloys, which have been achieved for a whole range
of systems. In this process, enhanced solute concentration is obtained
through the local mixing induced by each irradiation event, which if
occurring at a high enough frequency, can outweigh demixing by thermal
diffusion. The resulting microstructure forms in far from equilibrium
conditions, and theoretical results for these kind of driven alloys have
shown that novel microstructures exhibiting self-organization can develop.
To test these predictions, we prepare Ag-Cu multilayered thin films that we
subject to 1 MeV Kr+-ion irradiation at temperatures ranging from
room temperature to 225 °C, and characterize the specimens by x-ray
diffraction, TEM and STEM. We observe two different phenomena occurring at
different length scales: On the one hand, regardless of the irradiation
temperature, grains grow under irradiation until reaching a size limited by
film thickness (~200 nm). On the other hand, the distribution of species
inside the grains is greatly affected by the irradiation temperature. At
intermediate temperatures, a semi-coherent decomposition is observed at a
nanometer scale. This nanometer-scale decomposition phenomenon appears as an
evidence of patterning, and thus confirms on the possibility of using
ion-beam irradiation as a route to synthesize nanostructured materials with
novel magnetic and optical properties.