Diffusion barriers play an important role in numerous phase formation processes. A well known example in microelectronics is the reactive diffusion growth of silicide thin films which are applied as contact materials. In this work, the effect of a Ti interlayer on the kinetics of the formation of CoSi by reactive diffusion is investigated. Therefore, Co(100 nm)/Ti(5 nm) deposited on Si(111) is annealed at various temperatures. Transmission electron microscopy and atom probe tomography allow