Spontaneous roughening and vacancy dynamics on Si(100)-2x1:Cl

In this Letter we provide real-time STM evidence for spontaneous roughening on Cl-terminated Si(100)-2 x 1 surfaces. Dimer vacancy strings are shown to dissociate into individual single-atom vacancy strings. These strings can be separated by single or double rows of Si dimers, producing regions with local 3 x 2 and 5 x 2 structures, respectively. The dynamical rearrangements reported here are driven by the reduction in steric interactions on the roughened surface. For Cl, the driving force is small and these local rearrangements are often reversible. However, certain vacancy configurations pin the rearrangement yielding stable surface structures. (C) 2002 Elsevier Science B.V. All rights reserved.