The long-range migration of H at 180 to 310C was studied in radio-frequency sputter-deposited hydrogenated amorphous material by using transmission electron microscopy and infra-red absorption techniques. The results were described by:

5.0at%H, diffusion length = 90nm:     D (cm2/s) = 1.7 x 10-4 exp[-1.21(eV)/kT]

5.0at%H, diffusion length = 150nm:     D (cm2/s) = 6.3 x 10-5 exp[-1.19(eV)/kT]

6.0at%H, diffusion length = 120nm:     D (cm2/s) = 4.7 x 10-6 exp[-1.00(eV)/kT]

6.0at%H, diffusion length = 150nm:     D (cm2/s) = 3.7 x 10-6 exp[-1.01(eV)/kT]

6.0at%H, diffusion length = 200nm:     D (cm2/s) = 2.6 x 10-6 exp[-1.02(eV)/kT]

7.4at%H, diffusion length = 120nm:     D (cm2/s) = 1.2 x 10-8 exp[-0.74(eV)/kT]

7.4at%H, diffusion length = 150nm:     D (cm2/s) = 1.2 x 10-8 exp[-0.76(eV)/kT]

7.4at%H, diffusion length = 200nm:     D (cm2/s) = 6.2 x 10-8 exp[-0.86(eV)/kT]

9.5at%H, diffusion length = 90nm:     D (cm2/s) = 9.7 x 10-8 exp[-0.75(eV)/kT]

9.5at%H, diffusion length = 150nm:     D (cm2/s) = 2.2 x 10-9 exp[-0.77(eV)/kT]

It was found that the diffusion coefficient decreased with time, according to t-β. In films with an initial H content of between 5 and 7.4at%, the value of β was approximately equal to 0.4 and was independent of temperature and H content. In films with a H content of 9.5at%, β was approximately equal to 0.65 and did not depend upon the temperature. The H content decreased during annealing at temperatures which were as low as 180C. The diffusion of H to the nearest microvoids, and recombination at their surfaces, were suggested to affect the value of β strongly. The activation energy and the pre-exponential factor ranged from 0.7 to 1.2eV and from 2.2 x 10-9 to 1.7 x 10-4cm2/s, respectively. The data for the various samples obeyed the Meyer-Neldel rule.

X.L.Wu, R.Shinar, J.Shinar: Physical Review B, 1991, 44[12], 6161-8