The migration of Na in glasses, during electron probe microanalysis, was investigated. The change in X-ray emission as a function of time and electron dose was observed, and an exponential decay of the Na signal was clearly established. The model for Na+ migration was based only upon an electric field with a linearly decreasing behavior as a function of depth, and accounted for the main experimental results; with no evidence of an incubation time before ion migration. The electron densities, and the fraction of incident electrons which remained trapped in the glass, were deduced from estimates of the ion mobility.

O.Jbara, J.Cazaux, P.Trebbia: Journal of Applied Physics, 1995, 78[2], 868-75