Surface stacking sequence and (7 × 7) reconstruction at Si(111) surfaces

The (7 ×{} 7) surface is considered to have a triangular checkerboard structure in which the layer stacking sequences ⋯AaBbA and ⋯AaCcA alternate in neighboring triangular subunits in conformity with ion-backscattering results. The topological requirements of joining double layers at the subunit boundaries lead to the prediction of arrays of dimers and of deep (6.3-{}) holes which are consistent with results of electron diffraction and of tunneling microscopy, respectively.