Evolution of concentration profiles in Pd–Cu systems studied by SNMS technique

•Interdiffusion in Pd/Cu bilayer system was studied by SNMS technique.•Formation of high concentration phases was explained by means moving grain boundaries.•From the measured profiles we evaluated Cu grain boundary diffusivities in Pd.

Interdiffusion in polycrystalline Pd–Cu thin film system was investigated in the temperature range of 120–310 °C, by means of SNMS depth profiling technique. Depending on the annealing parameters, an almost complete homogenization was detected even at temperatures, where the volume diffusion was frozen in. In the Pd layer, the detected Cu profiles and their time evolution were typical C-kinetic regime grain boundary profiles at short annealing times. Because of the much higher grain boundary diffusivity on the Cu-rich side, the saturation of Cu grain boundaries is reached in very short times. In Pd-side, from the time evolution of C-type depth profiles, we determined the Cu grain boundary diffusion coefficients at different temperatures. The high concentration level in Cu-side could be interpreted supposing moving boundaries that leave behind regions with high Pd concentration.Though the intermetallic phase formation in this system under similar conditions was proved, the shape of our depth profiles does not show any effects of a reaction layer formation near the original interface. Our findings remain compatible with the previous results, if we suppose an unconventional type of growth mode: phase formation takes place in and around grain boundaries, by means of transport along moving grain boundaries/interfaces.