AES investigations on low-temperature interdiffusion in Thin Au films on Ag (111) substrates

The capability of studying low-temperature thin film/substrate interdiffusion by AES and ion sputter etching is demonstrated by the example of epitaxial Au films on Ag(111). The diffusioninduced changes of concentrations in both, surface and volume are determined at temperatures between 200 and 400 °C for Au film thicknesses ranging from 5 to 100 monolayers. To guarantee a correct data interpretation complementary information regarding Auger emission parameters, surface segregation, sputter-induced falsifications, effects of short-circuit diffusion, and film morphology is gathered from additional investigations performed by AES and TEM. The experiments reveal a strong concentration dependence of the coefficient of interdiffusion. The activation energies of 1.62 and 1.95 eV measured at vanishing Ag and Au concentrations, respectively, indicate that a pure monovacancy mechanism is operative contrary to the high-temperature diffusion where vacancy complexes are involved. For Au film thicknesses below 20 monolayers quantitative measurements become problematic since size effects occur that are due to both, modifications in the atomic bonding and surface diffusion.