Atomic and electronic structure of the Si(001)2 x 1-Li chemisorption system at 1.0 monolayer coverage

Systems involving the interaction of alkali metals with silicon surfaces have attracted attention in semiconductor surface science due to both fundamental interest and possible technological applications. Ab initio plane-wave pseudopotential density functional theory (DFT) calculations have been performed to determine the atomic and electronic structure of the Si(001)2 x 1-Li adsorption system at 1.0 monolayer (ML) coverage. Chemisorption of the lithium atoms is found to result in a minimum energy configuration characterized by symmetric Si dimers in agreement with the results of high-resolution core-level photoelectron spectroscopy. The transition from the asymmetric Si dimers of the clean Si(001) surface to the symmetric dimers of the Li chemisorbed surface is due to charge transfer from the Li adatoms to the substrate. The dispersion of the occupied electronic surface state bands is found to be in good agreement with the angle-resolved photoemission data. The nature of the lowest energy unoccupied surface state band suggests that silicide formation may occur at coverages greater than 1.0 ML.