MISSING-ROW ASYMMETRIC-DIMER RECONSTRUCTION OF SIC(001)-C(4X2)

A new reconstruction model for the cubic SiC(001)-c(4 x 2) surface is suggested on the basis of ab initio pseudopotential total energy and g rand canonical potential calculations. Our results clearly favor an ad atom structure with half a monolayer of Si atoms adsorbed at the Si-te rminated surface. The adatoms form a missing-row reconstruction with s trong asymmetric dimers whose bond length is 2.3 Angstrom. The model e xhibits a semiconducting surface and it is in good accord with recent experimental data. The previously suggested alternatively up- and down -dimer model turns out to be neither a stable nor a metastable structu re.