Abstract
The previously proposed triangle-dimer model of the Si(111)−7 × 7 surface [E.G. McRae, Surface Sci. 124 (1983) 106] is modified to conform to wurzite-like surface stacking sequences implied by Rutherford backscattering results. 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. The topological requirements of joining double-layers across the subunit boundaries lead to the prediction of a deep (6.3 Å) hole at the subunit apex and of alternating dimers and deep holes along the subunit sides. The new model is shown to be substantially in accord with low energy electron diffraction, high energy transmission electron diffraction, hydrogen chemisorption, high-resolution infrared spectroscopy, scanning tunnelling microscopy and physisorption experiments. All known qualitative disagreements with experiment are noted. It is suggested that the driving force of the 7 × 7 reconstruction is the backbonding of surface atoms to atoms directly beneath them. A dislocation mechanism of 7 × 7 reconstruction is proposed.
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