It was recalled that amorphous silicon nitride was a model system, for a covalently bound amorphous solid with a low atomic mobility, for which values of the self-diffusivity were lacking. Neutron reflectometry of isotope-enriched Si314N4/Si315N4 multi-layers was used to determine N self-diffusivities ranging from 10-24 to 10-21m2/s between 950 and 1250C (figure 1). Time-dependent diffusivities, observed at 1150C, indicated the presence of structural relaxation. For long annealing times (relaxed state), the diffusivities obeyed an Arrhenius relationship - with an activation enthalpy of 3.6eV. The results indicated a direct diffusion mechanism which did not involve thermal point defects.

Nitrogen Diffusion in Amorphous Silicon Nitride Isotope Multilayers Probed by Neutron Reflectometry. H.Schmidt, M.Gupta, M.Bruns: Physical Review Letters, 2006, 96[5], 055901 (3pp)