ORIGIN OF THE SYMMETRICAL DIMERS IN THE SI(100) SURFACE

A phase defect consisting of a phase boundary in a dimer row was obser ved to exist and migrate in the symmetric dimer region of a Si(100) su rface at about room temperature. When the phase defects migrate rapidl y compared to the timescale of scanning tunneling microscopy (STM), it results in a symmetric image of dimers. In this case, since dimer fli p-flop motion is limited to the domain boundaries of the dimer rows, m ost of the surface remains unchanged without the destruction of the 2x anticorrelation of the buckled dimers along the dimer rows. Consideri ng the obtained results and the fact that the electronic structures ob tained by photoemission spectroscopy at room temperature agree well wi th the theoretical results calculated for a surface with asymmetric di mer structures, the symmetric dimer structure observed at room tempera ture is concluded to be caused by the characteristic properties of the phase defects.