Stacking-fault model for the Si(111)-(7×7) surface

We propose a model for the geometric structure of the Si(111)-(7×{}7) surface based on a stacking fault in the surface layers. The model quantitatively accounts for existing ion-channeling data. Additional evidence for the stacking fault is given by constant-momentum-transfer averaged low-energy electron-diffraction data. A specific class of superlattice structures is suggested by the occurrence of two nearly equivalent stacking sequences having triangular symmetry.