Sn-induced c(4×4) reconstruction on the C-incorporated Si(001)-4^∘ off surface

The reconstruction induced by Sn atoms on the C-incorporated Si(001)-4^∘ off surface has been studied using scanning tunneling microscopy and synchrotron photoemission spectroscopy. When 0.6-ML Sn atoms were deposited on the Si(001)-4^∘ off surface with subsurface C atoms at 630 °C, the whole (001) terraces were covered with a single c(4×4) reconstruction, where each Sn addimer bridges two Si dimers, reducing the density of dangling bonds to 0.5 ML. Such a reconstruction is different from the Sn-induced c(8×4) reconstruction formed on the clean Si(001) terraces without subsurface C atoms, where Sn dimers replace Si dimers and every fourth dimer is vacant. In both cases, the adjacent dimers buckle out of phase and the D_B steps are debunched into single-layer steps. The reconstruction change from c(8×4) to c(4×4) is explained by the surface stress exerted by the subsurface C atoms much smaller than Si atoms.