Is. Hwang et al., Scanning tunneling microscope study of dynamic phenomena on clean Si(111) surfaces: Si magic clusters and their role, J PHYS CH S, 62(9-10), 2001, pp. 1655-1671
On Si(111) surfaces, we observed a special type of Si magic clusters with a
variable-temperature scanning tunneling microscope (STM). At temperatures
above 400 degreesC, these clusters migrate on Si(111)-(7 X 7) surfaces as a
whole. They can hop within a half-cell of Si(111)-(7 X 7), but sometimes t
hey hop away from their original halves, leaving the 7 X 7 structure intact
. When this happens, the magic cluster usually reappears at a site a few hu
ndred A away. We characterize its structure and derive path-specific hoppin
g parameters using Arrhenius analysis. In the long hops, interestingly, mag
ic clusters exhibit a strong bias for moving in the direction of the heatin
g current. Effects of the directed motion in electromigration and those in
thermal migration are determined separately and quantitatively. We also obs
erved fluctuations of step edges through detachment and attachment of magic
clusters. The filling of two-dimensional (2-D) craters and the decay of 2-
D islands are also found to occur preferentially at the cathode side. These
observations provide important clues for understanding the atomic processe
s in epitaxial growth and in electromigration on Si(111) surfaces. Based on
our observations, the phase transition of 7 X 7 <----> 1 X 1 is also discu
ssed. (C) 2001 Elsevier Science Ltd. All rights reserved.