The migration of D on the (111) plane of a W field emitter was studied by using the fluctuation method. Both activated and non-activated diffusion was observed. As the latter exhibited a very small isotope effect, it was suggested that mass renormalization caused the effective masses of H and D to be essentially identical. The diffusivity values in the temperature-independent regime ranged from 5 x 10-14 to 10-13cm2/s; depending upon the coverage. At a coverage of 1 monolayer, the data were described by:

90-111K:     D (cm2/s) = 2 x 10-9 exp[-2.1(kcal/mol)/RT]

125-200K:     D (cm2/s) = 7 x 10-8 exp[-4.6(kcal/mol)/RT]

200-250K:     D (cm2/s) = 1.4 x 10-5 exp[-7.5(kcal/mol)/RT]

At a coverage of 0.75 of a monolayer, the data were described by:

105-125K:     D (cm2/s) = 6.8 x 10-8 exp[-2.9(kcal/mol)/RT]

200-250K:     D (cm2/s) = 1 x 10-5 exp[-7.2(kcal/mol)/RT]

C.Dharmadhikari, R.Gomer: Surface Science, 1984, 143[1], 223-42