Roughness and structural motifs on the Si(1 0 3) surface

Si(1 0 3) is a stable nominal orientation of silicon crystals which was shown experimentally to be rough and disordered on the atomic scale. In this paper, we investigate 2 × 2 structures of the Si(1 0 3) surface retrieved via a genetic algorithm optimization. We have found a number of atomic scale structural motifs that are common to most of the 2 × 2 low-energy reconstructions. These reconstructions are assemblies of motifs with different types, numbers, and relative positions within the 2 × 2 surface unit cell. This analysis leads to the idea that the disorder on Si(1 0 3) could stem not only from the presence of several reconstructions with similar surface energies and diverse morphologies, but also from the fact that the structural motifs can be assembled together in variety of configurations apparently without incurring large energetic penalties and without having to form periodic patterns. This result is supported by molecular dynamics simulations of large-area Si(1 0 3) systems which show that the structural motifs can be retrieved individually (rather than in the prescribed combinations such as those retrieved by the genetic algorithm) at temperatures around 1000 K.