Comment on “Atomic structure model of the reconstructed Si(557) surface with a triple step structure: Adatom-parallel dimer model”

Abstract

Recently, [Oh et al.Phys. Rev. B 77, 155430 (2008)] reported on an atomic model for the so-called Si(557)-reconstructed surface with regular triple steps. The atomic structure model proposed was developed on the basis of high-resolution scanning tunneling microscopy (STM) images and first-principles calculations performed to match such STM images. Here we argue that the STM image presented is affected by an artifact, most likely related to a multiple tip image effect. Among other issues with the image presented, the corner holes for $(7\ifmmode\times\else\texttimes\fi{}7)$ reconstruction on Si(111) terraces are not visible, since a doubled image superimposed smears out such characteristic depression. The $(\ifmmode\times\else\texttimes\fi{}7)$ periodicity deduced for the edge facets, in contrast with previously reported STM images and electron-diffraction studies which unambiguously indicate a $(\ifmmode\times\else\texttimes\fi{}2)$ periodicity, arises from the same artifact. Finally, we remark that the (557) surface orientation and (112) orientation of triple steps assumed for first-principles calculations disregard the latest experimental data available, which suggests this surface has a (7 7 10) orientation and the steps in triple step do not form a well-defined plane [Surf. Sci. 600, 4878 (2006)].