Surface Self-Diffusion of Atoms and Atom Pairs

Quantitative observations have for the first time been made of the surface diffusion of single self-adsorbed tungsten atoms and atom pairs. Measurements on the (211) plane indicate that motion of single atoms is normal, occuring over a barrier of 74 kJ/mole, with a pre-exponential factor $D_0={10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$/sec. Motion of pairs formed by atoms in adjacent [111] channels is highly correlated; it involves a much smaller barrier, 28 kJ/mole, and a pre-exponential factor of only ${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^2$/sec.