To investigate the Al migration in Ag, Ag (100 nm)/Al (10 nm) bilayer structures were grown on (1 1 1) Si substrates using molecular beam epitaxy. The grown bilayers were annealed in situ at different temperatures between 25degreesC and 500degreesC (under similar to10(-8) Torr vacuum) and X-ray photoelectron spectra were recorded as a function of annealing time. Even at room temperature, Al was found to migrate to the top of the Ag layer, where it reacted with residual oxygen present in the chamber and formed Al2O3. The thickness of the so-formed Al2O3 overlayer is found to increase with logarithmic of annealing time. The atomic force microscopic studies show that Al diffusion primarily occurs through grain boundaries. (C) 2003 Elsevier B.V. All rights reserved.