Mrs. Hagit Barda, Ph.D. Candidate
Department of Materials Science and Engineering,
Technion – Israel Institute of Technology Haifa 3200003, Israel
Thin metal films deposited on ceramic substrates tend to dewet (agglomerate) upon thermal annealing. The final result of this process is an array of isolated faceted metal particles attached to the substrate. It is generally believed that the solid state dewetting is controlled by surface diffusion. Based on the indirect evidence we proposed that Ni atoms rejected by expanding hole might accumulate beneath the Ni film by the mechanism involving Ni self-diffusion along the Ni-sapphire interface. We developed several new methods of direct tracking of the atom movements at the interface. For studying the heterodiffusion of Au along the Ni-sapphire interface we deposited an ultra-thin Au layer on partially dewetted thin Ni film deposited on sapphire. Tracking the penetration of Au along the interface by various transmission electron microscopy techniques allowed determining respective interface heterodiffusion coefficients. The obtained interface diffusivities were higher than bulk diffusion coefficient of Au in Ni, but lower than Au diffusivity along the large-angle grain boundaries in Ni. Furthermore, we performed two marker experiments for estimating the relative contributions of interface and surface self-diffusion to the solid state dewetting. The displacement of Si marker sandwiched between two Ni layers on sapphire was interpreted in terms of interface self-diffusion of Ni during initial stages of dewetting (grooving). The negligible displacement of the Cr2O3 markers beneath the growing hillocks indicated that the latter grow by the surface diffusion mechanism.