Ca-induced intermediate reconstructions on the Si(111) surface

Abstract

The geometric and electronic properties of the Ca-induced intermediate reconstructions on the Si(111) surface, particularly $\text{Ca}/\text{Si}(111)\text{\ensuremath{-}}(5\ifmmode\times\else\texttimes\fi{}n)$ with $n=1$, 2, and 4, are theoretically investigated using the pseudopotential method and the local-density approximation (LDA) of the density-functional theory. The geometrical models for the three reconstructions are based on deposition of different Ca lines on the top of a combination of a honeycomb chain channel and a Seiwatz chain formed by Si atoms. These structural models are found to produce semiconducting surface band structures with clear LDA energy gaps. We have identified one, three, and four surface states within the bulk band gap for the $(5\ifmmode\times\else\texttimes\fi{}1)$, $(5\ifmmode\times\else\texttimes\fi{}2)$, and $(5\ifmmode\times\else\texttimes\fi{}4)$ reconstructions, respectively. The relative stabilities of these reconstructions are discussed as a function of Ca coverage. Significant charge transfer from the Ca adatoms to neighboring Si atoms has been concluded by analyzing electronic charge density and scanning tunneling microscopy simulations.