Diffusion and phase stability in ion irradiated Cu/Pd thin films

The interdiffusion and the stability of the β phase under 300 keV Cu+ ion irradiation were investigated in Cu/Pd thin films between 293 and 573 K using Rutherford backscattering spectrometry. The interdiffusion coefficient below 373 K normalized to the displacement rate K' describes atomic mixing and amounts to Dmix/K'=1.9 nm2/dpa. From the dependence of the radiation-enhanced interdiffusion coefficient on temperature and displacement rate above 373 K, the production rate of freely migrating defects of about 0.02 K', the effective sink concentrations of about 10-5 and the migration energy for the vacancy of about 0.8 eV are drived. The β phase in the thin film diffusion couple was identified by concentration steps in the depth profiles. Below 423 K the steps disappear after irradiation at 1.5x10-4 dpa/s to fluences around 5.4 dpa indicating the dissociation of the β phase. Irradiation above 503 K to a fluence of 54 dpa at 1.5x10-2 dpa/s induces growth of the β phase layer. From the results the stability of the β phase layer under irradiation is interpreted in terms of the fundamental damage processes. (orig.)