ON MECHANISMS OF DIFFUSION IN INERT-GAS BOMBARDED SOLIDS . DIFFUSION THEORY FOR DISCRETE MEDIA .5.

Diffusion in inert-gas bombarded solids can be described in terms of five basic processes. Stage IA, provided it is correctly attributed to gas fortuitously located in high-mobility sites, would be treated using diffusion theory with a trapping term. The total fraction of gas escaping, Fia, should be given by the relation FIA-1 = I + R ̄/L, where R ̄ is the 1/e range and L is the appropriate diffusion length for trapping. Stage IB, due to gas being swept out by the annealing of bombardment-induced disorder, should occur in an amount FIB given by the relation (1-FIB)-1 ≈ 1 + 1.7 Bt(V(d) 4 3)/ R ̄2, where Bt is the bombardment dose and Vd is the volume disordered per ion impact. Stage IIA, which is probably due to gas in sites similar to normal substitutional sites, can be safely assumed to be described by the usual diffusion equation. It shows a marked correlation with selfdiffusion such that the following is true: TIIA = (0.86 ± 0.10)Tself-diffusion, where T stands for absolute temperature. Stage IIB is similar to IIA except that it appears to involve transient gas-gas or gasdamage interactions. The predicted amount, FIIB, should be given by the relation (1-FIIB)-1 = 1 + R ̄/L, where L is now the diffusion trapping length' appropriate to gas-gas or gas-damage encounters. Stage III is generally accepted to reflect the motion of stable, gas-filled bubbles, and should, if this is so, be adequately described by the usual diffusion equation, though with-Duubbie substituted for D. © 1969.