The evolution of sub-monolayer 2-dimensional Au phases on the (111)-(7 x 7) surface was studied in real time by using spectroscopic photo-emission and low-energy electron microscopy involving a synchrotron radiation source. A finite area, covered with 1 monolayer of Au, with a step-like transition zone, was prepared by in situ evaporation. Subsequent annealing resulted in spread of the Au layer, and the formation of laterally extended (111)-(5 x 1)-Au and (111)-(3√ x √3)R30°-Au surface reconstructions. At a temperature of about 970K, the boundary of the Au-covered region propagated on the clean (111)-(7 x 7) surface and exhibited a non-linear time-dependence. The ordered (111)-(5 x 1)-Au plateau developed a separate front which moved with constant velocity. Two values of the Au diffusion coefficients were estimated for a temperature of about 985K. The average diffusion coefficient for Au on a clean (111)-(7 x 7) surface was equal to 5.2 x 10-8cm2/s for concentrations ranging from 0.4 to 0.66 of a monolayer. The lower limit for the diffusion of single Au atoms on the (111)-(5 x 1)-Au ordered phase was equal to 1.2 x 10-7cm2/s.

Surface Diffusion of Au on Si(111): a Microscopic Study. J.Slezák, M.Ondřejček, Z.Chvoj, V.Cháb, H.Conrad, S.Heun, T.Schmidt, B.Ressel, K.C.Prince: Physical Review B, 2000, 61[23], 16121-8