A new alternative model of type-C defects on Si(1 0 0) surfaces

On the basis of first-principles total-energy electronic-structure calculations, we propose a new microscopic model of type-C defects on Si(1 0 0) surfaces. In the model, a hydrogen atom and a hydroxyl which are dissociated from H2O molecules in residual gases are adsorbed on the same side of two adjacent Si dimers along the 〈0 1 1〉 direction. Calculated STM images show that a Si atom which is decorated by either H or OH appears as a dark spot at both bias polarities, and that the opposite dangling-bond sites of the two dimers become bright protrusions in the empty-state image. Other characteristics in the observed images of the type-C defects are also discussed.