The electromigration of Si on (111)-(7 x 7) surfaces was observed by using scanning tunnelling microscopy. The diffusing species were identified as being Si magic clusters. The quantitative effects of directed motion (along the direction of the heating current) in electromigration, and those of thermal migration, were determined separately. The preferential filling of 2-dimensional Si craters was observed, as was the preferential detachment of Si magic clusters from the edges of 2-dimensional Si islands near to the cathode side. The driving force for this anisotropic behavior was much higher than had previously been recognized.

Direct Observation of Electromigration of Si Magic Clusters on Si(111) Surfaces. M.S.Ho, I.S.Hwang, T.T.Tsong: Physical Review Letters, 2000, 84[25], 5792-5