Published online by Cambridge University Press: 15 February 2011
Nuclear magnetic resonance (NMR) measurements of 1H dipolar echoes in a-Si:H indicate that the dipolar spin-lattice relaxation time, T1D, can be used as a measure of local hydrogen motion. In general, the microscopic hydrogen motion is orders of magnitude faster, and the microscopic activation energies are much smaller, than those measured macroscopically using secondary ion mass spectroscopy (SIMS). Although no detailed model exists to explain these apparently divergent results, these discrepancies can be understood phenomenologically by assuming a very broad distribution of rates. In this case the measured activation energies can be shown to scale roughly as the logarithm of the time over which the measurement is made.