The reconstruction of the Si(001)-(2 x 1) surface consisted of asymmetrical and buckled Si dimers. The vertical separation between the up and down atom within the dimer was about 0.72Å, and the dimer bond length of 2.24Å has been found to be slightly smaller than the Si-Si distance in the bulk. The tilt of the dimer was 19°. The formation of Si dimers induced marked distortions of the substrate that were detectable down to the fifth Si layer.

Surface Atomic Geometry of Si(001)-(2x1) - a Low-Energy Electron-Diffraction Structure Analysis. H.Over, J.Wasserfall, W.Ranke, C.Ambiatello, R.Sawitzki, D.Wolf, W.Moritz: Physical Review B, 1997, 55, 4731-6