Observation of domain boundaries on the Si (111) 7×7 surface by scanning tunneling microscope

A highly reliable scanning tunneling microscope system equipped with a field ion microscope yielded successful observation of a domain boundary on the Si(111) 7×7 reconstructed surface. For the first time, we revealed its detailed structure at the atomic level. The boundary consists of holes far larger than the corner holes of the dimer-adatom-stacking fault (DAS) model and bridge-like structures with three 2×2 subunits. The ditch structure of this boundary is running to the [1̄10] direction, i.e., to the direction of the shorter diagonal of the 7×7 unit cell. We discussed that a misfit of the 7×7 periodicity between the neighboring domains caused this ditch structure.