The H was implanted into crystalline samples at 40 to 300K. At low implantation energies, a large fraction of the H was mobile while the rest remained trapped at up to 500K. At temperatures above 200K, the present data (table 176) agreed with the established Arrhenius behavior, which was characterized by an activation energy of 0.5eV and a pre-exponential factor of about 0.01cm2/s. At temperatures below 200K, the data obeyed a power law, and the temperature exponent of 5.6 indicated the occurrence of a tunnelling mechanism. The diffusion in this range was unaffected by the Fermi-level position.

S.Fabian, S.Kalbitzer, C.Klatt, M.Behar, C.Langpape: Physical Review B, 1998, 58[24], 16144-53