Thin film interreaction of Al/Ag analyzed by tomographic atom probe

A nanoanalytical study of Ag/Al interreaction by atom probe tomography is presented. For that, metallic thin films are deposited on tungsten substrate tips by ion beam sputtering. The Al/Ag reaction couple qualifies as a particularly clear model system due to its simple phase diagram and the identical lattice structure of both reacting materials. Nevertheless, the tomographical analysis demonstrates that the reaction does not proceed on a planar layer geometry. Instead, after annealing at 100 °C for 15 min, a three-dimensional reaction morphology develops caused by fast grain boundary transport. During further annealing, at first a metastable phase of 67 at.% Al is observed. The expected equilibrium Ag2Al is only formed in late reaction stages by a precipitation process.