Carbon lines on the cubic SiC(001) surface

We investigated the structure and bonding of carbon atomic lines on the beta-SiC(001) surface, using ab initio calculations. In agreement with experiment, we find that reconstructions with sp-bonded chains are energetically favored over those with sp(3)-like C bonds. However the energy difference between the two types of reconstructions is only a few meV/dimer, and for small applied compressive stress geometries with sp(3)-bonded sites become favored, in addition, the formation energy of sp(3)-like defects on a sp-bonded surface decreases rapidly with increasing defect concentration, pointing at stable sp(3) lines perpendicular to sp dimers, consistently with experiment. A mechanism is proposed for the recently observed sp --> sp(3) transition on carbon terminated beta-SiC(001) surfaces.