Origin of buckling-dimer-row formation of Si(001) surfaces

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Abstract
Structural transformations of dimer rows on 2×1-reconstructed Si(001) surfaces have been investigated with ab initio quantum theoretical calculations. It has been revealed that the adsorption of Li or H atom induces the buckling of the dimer at the adsorbed site, and this buckling propagates along the dimer-row to produce a zigzag dimer row structure. There appear extra filled- and empty-state band structures near the Fermi level, which consist of occupied and unoccupied molecular orbitals localized on the upper- and lower-side Si atoms of buckled dimers, respectively. Scanning tunneling microscopy images obtained in a zigzag dimer row on Si(001) surfaces have been demonstrated to reflect the spatial distributions of electrons in these extra bands. The origin of the buckling propagation is explained by electron distribution on the surface, and dimer-row structures at low or room temperature have also been discussed. © 1996 The American Physical Society.