Surface diffusion of Au on Si(111): A microscopic study

The direct evolution of submonolayer two-dimensional Au phases on the (Formula presented) surface was studied in real time using the spectroscopic photoemission and low energy electron microscope located at the synchrotron radiation source ELETTRA. A finite area covered by 1 monolayer (ML) of gold with a steplike transition zone was prepared by evaporation in situ. Subsequent annealing resulted in the spread of the Au layer and the formation of laterally extended (Formula presented) and (Formula presented) surface reconstructions. At a temperature around 970 K, the boundary of the gold-covered region propagates on the clean (Formula presented) and exhibits a nonlinear dependence on time. The ordered (Formula presented) plateau develops a separated front moving with constant velocity. Two values of the Au diffusion coefficients were estimated at a temperature of about 985 K: (1) (Formula presented) as the average diffusion coefficient for Au on a clean (Formula presented) surface in the concentration range from 0.4 ML up to 0.66 ML and (2) (Formula presented) as the lower limit for the diffusion of single Au atoms on the (Formula presented) ordered phase.