A Monte Carlo study of oxygen diffusion on the (110) plane of tungsten was carried out, by finding the time autocorrelation function of particle number fluctuations on a square lattice. Best results were obtained by the single site autocorrelation function, but did not differ much from those obtained from a finite probed region. The experimentally observed increase in activation energy with coverage could be reproduced almost quantitatively by using an attractive nearest neighbor interaction energy J1 = 2.1kcal, a repulsive next-nearest neighbor energy J2 = -1.7kcal, an attractive third nearest-neighbor energy J3 = 0.7kcal and a triplet energy Jt = 0 or -1.2kcal. With those parameters an increase in pre-factor of > 100 was seen as coverage increased from 0 to 0.5. This increase still falls short of the experimentally observed one, as expected. The mean square number fluctuation was also calculated using the values of J1, J2 and J3 cited above in the grand canonical ensemble as function of temperature and coverage. The results agreed qualitatively with the experimental ones, but were an order of magnitude larger.

A Monte Carlo Study of Oxygen Diffusion on the (110) Plane of Tungsten. M.Tringides, R.Gomer: Surface Science, 1984, 145[1], 121-44