The migration of 1H and 2H upon the (111) and (100) surfaces of a field emitter was studied by using a fluctuation method. It was found that activated and tunnelling diffusion occurred on both surfaces. On the (111) surface, the activation energy for the diffusion of 1H was equal to about 3kcal at low coverages, increased to about 4kcal at higher coverages, and then slightly decreased. The behavior of the activation energy for 2H diffusion mirrored that of the 1H activation energy, but was 0.4kcal higher. The pre-exponential factor for 1H diffusion was equal to 0.0003cm2/s at low coverages, increased to 0.07cm2/s at mid-coverage, and then decreased again. The corresponding values for 2H diffusion were only slightly different. The tunnelling diffusion coefficients were of the order of 10-10cm2/s for both isotopes; with only a small dependence upon coverage. On the (100) surface, the activation energy for the diffusion of 1H was equal to 3.2kcal, regardless of the coverage. The activation energy for 2H diffusion was equal to 3.6kcal, regardless of the coverage. The pre-exponential factor for 1H diffusion was equal to 8 x 10-6cm2/s at low coverages, and remained essentially constant. The corresponding value for 2H diffusion was equal to 2 x 10-5cm2/s at low coverages and increased to 0.0002cm2/s at high coverages.

Diffusion of 1H and 2H on the Ni(111) and (100) Planes. T.S.Lin, R.Gomer: Surface Science, 1991, 255[1-2], 41-60