Step and kink dynamics on Au(110) and Pb(111) studied with a high-speed STM

The dynamics of monoatomic steps on the Au(110) surface is studied with a scanning tunneling microscope from room temperature to 590 K. The time dependence of the position fluctuations of steps was measured as a function of temperature and kink density. The mean-square displacement of the position was found to be proportional to the square root of time, indicating an exchange of atoms with the adjacent terraces. The step dynamics is dominated by the diffusion of geometrically forced kinks that perform a random walk but cannot pass each other. The statistics of step fluctuations in time is mapped on existing theory for one-dimensional diffusion. The resulting atomistic theory explains the time behavior of the mean-square step displacement and its dependence on both temperature and kink density. Kinks that are close together do not move completely independently of each other. The time dependence of the fluctuations of steps on Pb(111) indicates that the step motion of this surface is the result of mass transport along the step.