On (001)-type surfaces, an Ir adatom was found to jump along the [001]-type direction (instead of along the smoother close-packed [110]-type atomic channel of the substrate); probably via an atomic exchange mechanism. The sites which were visited by one diffusing adatom therefore formed a c(2 x 2) net in the substrate lattice. The displacement distributions which were derived were consistent with those which were expected on the basis of a discrete random walk having the atomic jump length of the nearest-neighbour distance of the c(2 x 2) net. The data could be described by:

D (cm2/s) = 0.0626 exp[-0.84(eV)/kT]

C.Chen, T.T.Tsong: Physical Review Letters, 1990, 64[26], 3147-50