Tests of Si(111)-7x7 structural models by comparison with transmission electron diffraction patterns.

Several structural models of the Si(111)-7x7 surface are tested by comparing calculated and observed transmission electron diffraction (TED) patterns. The models comprise "triangle- dimer" models where the unit mesh contains 9 dimers or sets of dimers bordering a triangular subunit of the unit mesh, and "adatom" models where the unit mesh contains 12 adatoms or atom clusters in a locally (2x2) arrangement. The distribution of diffraction intensity among fractional-order spots is calculated kinematically and compared with TED patterns observed by Petroff and Wilson and others. Good agreement is found for triangle- dimer models.