Origin of the symmetric dimers in the Si(100) surface

A phase defect consisting of a phase boundary in a dimer row was observed to exist and migrate in the symmetric dimer region of a Si(100) surface at about room temperature. When the phase defects migrate rapidly compared to the timescale of scanning tunneling microscopy (STM), it results in a symmetric image of dimers. In this case, since dimer flip-flop motion is limited to the domain boundaries of the dimer rows, most of the surface remains unchanged without the destruction of the 2x anticorrelation of the buckled dimers along the dimer rows. Considering the obtained results and the fact that the electronic structures obtained by photoemission spectroscopy at room temperature agree well with the theoretical results calculated for a surface with asymmetric dimer structures, the symmetric dimer structure observed at room temperature is concluded to be caused by the characteristic properties of the phase defects.