Dynamic behavior of Si magic clusters on Si(1 1 1) surfaces

On Si(1 1 1) surfaces, we observe a special type of Si magic clusters with a variable-temperature scanning tunneling microscope. They play a crucial role in many dynamic processes of the Si(1 1 1) surfaces. At temperatures above 400 °C, the magic cluster usually hops within a half-cell of Si(1 1 1)-(7×7), but sometimes it makes long-distance hops. We characterize its structure and derive path-specific hopping parameters using Arrhenius analysis. In the long hops, interestingly, the magic cluster exhibits a strong bias for moving in the direction of the heating current. Effects of the directed motion in electromigration and those in thermal migration are determined separately and quantitatively. We also observe fluctuations of step edges through detachment and attachment of magic clusters. The filling of two-dimensional (2D) craters and the decay of 2D islands are also found to occur preferentially at the cathode side. These observations provide important clues for understanding the atomic processes in epitaxial growth and in electromigration on Si(1 1 1) surfaces.