Atomic and electronic structure of Li-adsorbed Si(100) surfaces

Abstract

We investigate the atomic and electronic structure of Li-adsorbed Si(100) surfaces through first-principles pseudopotential calculations. We find that Li adatoms interact mainly with the dangling-bond orbitals of Si dimers, however, no hydrogenlike directional bonds exist between the Li and substrate Si atoms, based on calculated scanning tunneling microscopy images. The analysis of charge densities demonstrates a large charge transfer from the Li adatom to a dangling-bond orbital of a Si dimer, which is responsible for a large decrease of work function at submonolayer coverages. The Li atoms form linear chains either by occupying the interdimer bridge sites along the dimer row direction or the dimer bridge and cave sites perpendicular to the dimer row. As Li coverage (\ensuremath{\Theta}) increases, repulsive interactions between the adatoms in the chains are also found to increase. Thus, at 1-ML Li coverage, the stable adsorptions sites are changed to either the cave and pedestal sites or the valley-bridge and pedestal sites, with all the Si dimers symmetric, resulting in a $2\ifmmode\times\else\texttimes\fi{}1$ structure. From the calculated formation energies, we find a $1\ifmmode\times\else\texttimes\fi{}1$ phase to be thermodynamically stable at $\ensuremath{\Theta}=2,$ in contrast to other alkali-metal adsorptions.