Phase Transition between c (4×2) and p (2×2) Structures of the Si(100) Surface at 6 K Caused by the Fluctuation of Phase Defects on Dimer Rows due to Dimer Flip-Flop Motion

Dimers of the Si(100) surface previously observed at 120–140 K, which partially appeared to be symmetric, were frozen at 6 K, and an atomically resolved structural change between c(4×2) and p(2×2) arrangements of the Si(100) surface was observed for the first time by scanning tunneling microscopy. The observed change was due to the fluctuation of phase defects of a new type on dimer rows, which have a structure similar to that of the type-C defect. Dimer flip-flop motion at the phase boundary which induces the apparent phase transition, and creation and annihilation of the anti-phase domain were clearly observed.