The diffusion of W on a (211) plane of a W field emitter was re-examined by using the fluctuation autocorrelation method. It was found that diffusion along channels was described by:

D (cm2/s) = 3 x 10-5 exp[-16.8(kcal)/RT]

while diffusion across channels was described by:

D (cm2/s) = 4 x 10-9 exp[-6.6(kcal)/RT]

at temperatures below 752K, and by:

D (cm2/s) = 5 x 10-4 exp[-24(kcal)/RT]

at temperatures greater than 752K. The results for diffusion along channels yielded activation energies and pre-exponential factors which were intermediate between recent field ion microscopy results (19kcal, 0.0077cm2/s) and results (13.3kcal, 7 x 10-7cm2/s) which had been obtained by using the present method; but with a larger slit. The new high-temperature results suggested that the postulated channel wall exchange mechanism for cross-channel diffusion at low temperatures gave way to diffusion by climb (higher activation energy but higher pre-exponential factor) over the channel walls at temperatures above 752K.

D.S.Choi, R.Gomer: Surface Science, 1990, 230[1-3], 277-82