Hydrogen evolution transients were measured for hydrogenated amorphous
silicon prepared by Si implantation of crystalline silicon and subseq
uent hydrogen implantation. The evolution curves are found to be simil
ar for different H concentrations but with entirely different atomic a
nd nanoscale structures, as was evidenced by small-angle x-ray scatter
ing and infrared absorption investigations [Phys. Rev. B 53, 4415 (199
6)]. This behavior is explained by a hydrogen-diffusion controlled eff
usion with a limited density of sites in the amorphous material that c
an be occupied by hydrogen. The experimental effusion curves are model
ed by using diffusion coefficients in the implanted layers that were d
etermined by secondary-ion mass spectrometry. Diffusion through a high
ly disordered material of low H content is found to have an activation
energy of 2.26 eV. (C) 1997 American Institute of Physics.