Segregation effect on grain-boundary diffusion in thin metallic films

The diffusion in Au-Cu and Pt-Cu thin films has been studied by Rutherford backscattering sperctrometry (RES) under the kinetic regimes B (within the temperature interval of 175-290 degrees C) and C (room temperature). The 1.5-2.0 MeV He+ RES spectra were taken using 14-18 keV resolution. The RBS spectra were changed to depth-concentration profiles for both bulk and grain boundary (GB) diffusion. Under kinetic regime C the absolute values of GB diffusion coefficients were obtained. Under kinetic regime B the triple products delta K-b (delta is the GB width, D-b is the GB diffusion coefficient, K is the enrichment ratio) were obtained using the Whipple and Gilmer-Farrell models. The activation energies for GB diffusion of Au into Cu films and Cu into Au films are close to 0.95-0.98 eV atom(-1), whereas the activation energy for GB diffusion of Pt into Cu films is equal to 1.25 eV atom(-1). The comparison between the data on the GB diffusion for kinetic regime B extrapolated to room temperature and the data on the GB diffusion for kinetic regime C enables one to derive the product delta K and to separate the contribution of segregation to the parameters of GB diffusion for the systems under study.