The diffusion of individual N adatoms on Fe(100) was studied by using scanning tunnelling microscopy and ab initio density functional theory calculations. The measured diffusion barrier for isolated N adatoms was equal to 0.92eV; with a pre-factor of 4.3 x

1012/s. These were in quantitative agreement with the density functional theory calculations. The diffusion was strongly coupled to lattice distortions, and the presence of other N adatoms consequently introduced an anisotropy into the diffusion. The potential energy surface which was seen by a N adatom was determined on the basis of experimentally determined values of the diffusion barriers, and adsorbate-adsorbate interactions.

M.O.Pedersen, L.Osterlund, J.J.Mortensen, M.Mavrikakis, L.B.Hansen, I.Stensgaard, E.Lægsgaard, J.K.Nørskov, E.Besenbacher: Physical Review Letters, 2000, 84[21], 4898-901

Table 24

Diffusivity of 95Nb in α-Fe