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 diffusion-induced changes of concentrations in, surface and volume were determined at temperatures between 200 and 400 degree C for Au film thicknesses ranging from 5 to 100 monolayers. 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, modifications in the atomic bonding and surface diffusion.