The migration of 1H and 2H upon the (123) surface of a field emitter tip was studied by using the fluctuation method. The surface in question consisted of (110) terraces which were separated by (110)-oriented steps. That is, the step edges corresponded to close-packed rows of W atoms which ran along the (111) direction. The activation energies were similar to those which were found for (110). It was deduced that steps offered very little impediment to diffusion. At certain degrees of coverage, dips in the diffusivity were observed to occur in the activated regime. This behavior was attributed to the effect of phase transitions, and the coverages at which it occurred were different for the 2 isotopes. It was noted that tunnelling diffusion was associated with only a very small isotope effect. This was explained in terms of a mass dependence of the lattice distortions which were associated with tunnelling. This counteracted the mass dependence of pure H tunnelling.

D.S.Choi, C.Uebing, R.Gomer: Surface Science, 1991, 259[1-2], 139-50