ON THE TRANSPORT OF POINT-DEFECTS IN PASSIVE FILMS

Based on phenomenological equations and atomistic diffusion theory, ge neral equations have been derived for vacancy diffusion in solids. The normally used diffusion equations are found to be special forms of th e general equations under the assumption of low vacancy concentration or homogenous vacancy distribution. The general equations should be us ed to describe diffusion in solids that have high vacancy gradients, s uch as in barrier passive films. However, in the presence of a high el ectric field, vacancy gradient effects are considerably muted and the classical Nernst-Planck equations appear to be adequate for describing the transport of vacancies through the barrier layer. (C) 1997 Elsevi er Science Ltd.