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· The net flux of impurity atoms,
Jx,
will depend on the jump rate, the atom concentrations on the reference planes,
and a lattice geometry factor (α)
which characterizes the number of equivalent paths between the reference planes:
Jx
= {Net Flux} = {J+x - J-x} = α (NΑ - NC)
ν exp(-[ ΔGm + ΔGV]/kT)
· The Gibbs function barrier is symmetric for this case,
and the diffusion flux is zero if: NΑ = NC , i.e. a concentration gradient
(chemical
potential gradient) is needed for a vacancy diffusion mechanism
· The "energy" associated with
the vacancy diffusion mechanism contains both the energy of motion, ΔGm , and the vacancy formation
energy, ΔGV
.
· Comparing either the interstitial
or vacancy
mechanism expressions for the net flux with Fick's first law permits
D0
and Q to be computed in atomic terms.
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