Chemisorption-induced disruption of surface electronic structure: Hydrogen adsorption on theSi(100)−2×1surface

Abstract

The influence of hydrogenated Si(100) dimers on the geometry and electronic structure of neighboring bare dimers is studied by scanning tunnel microscope (STM) and ab initio calculations. Two coverage regimes are of interest. First, the presence of isolated hydrogenated dimers is shown to perturb neighboring bare dimers such that the barrier-for-dimer tilting is reduced with respect to that on the clean surface. At low temperatures this manifests itself in STM images as regions of continuously tilting $p(2\ifmmode\times\else\texttimes\fi{}1)$ bare dimers that fail to condense into the $c(4\ifmmode\times\else\texttimes\fi{}2)$ or $p(2\ifmmode\times\else\texttimes\fi{}2)$ structures characteristic of the clean surface. In the second case we studied the structure of isolated bare dimers on an otherwise completely hydrogenated Si(100) surface. These isolated bare dimers are weakly buckled compared to those on the clean surface and exhibit an enhanced $\ensuremath{\pi}\ensuremath{-}{\ensuremath{\pi}}^{*}$ energy splitting, in agreement with scanning tunneling spectroscopy studies. The spatial distribution of the \ensuremath{\pi} and ${\ensuremath{\pi}}^{*}$ density is significantly different from that found on the clean surface but corresponds closely to that seen in filled- and empty-state STM images.