Neutron reflectometry and isotope multilayers were used to investigate self-diffusion in covalent amorphous solids during isothermal annealing and its correlation to structural relaxation. Amorphous silicon nitride was chosen as a model system. Neutron reflectometry was a superior method to measure very low self-diffusivities, occurring in covalent solids, by applying only short time anneals. This permitted the determination of time-dependent changes in diffusivity over a broad temperature range before crystallization of the metastable solid occurred. The measured N diffusivities decreased by more than an order of magnitude upon annealing between 950 and 1150C, while at the same time there was also a decrease in the atomic density. This behavior was interpreted as being a structural relaxation of the amorphous network structure that was governed by the annihilation of interstitial-like defects.

Structural Relaxation and Self-Diffusion in Covalent Amorphous Solids - Silicon Nitride As a Model System. H.Schmidt, W.Gruber, T.Gutberlet, M.Ay, J.Stahn, U.Geckle, M.Bruns: Journal of Applied Physics, 2007, 102[4], 043516