Structural studies of Si (111) 2 × 1 surfaces using low-energy electron diffraction

The structure of the Si(111)2×1 surface is studied using dynamic low-energy electron diffraction analysis at three different off-normal electron incidence angles, with emphasis on the $\pi$-bond chain model. The optimum $\pi$-bond chain geometry has a buckling of 0.35 Å between the two chain atoms and a large distortion in the subsurface layer. The bond length of surface chains is determined to be 2.25±0.02 Å by detailed analysis. We compare our results with those of other authors.