Nature of bonding between alkali metals and silicon surface

In recent literature, diverse views have been expressed regarding the nature (ionic versus covalent) of bonding between alkali metals and the Si(001)-(2×1) surface. Also unsettled is the issue as to whether the metallicity upon K adsorption is due to the partial occupancy of the dangling bonds or due to the metallic K chain. The resolution of these outstanding problems is sought by performing electronic structure total energy calculations using cluster as well as slab models. The cluster model calculations have used an ab initio self-consistent field Hartree–Fock technique, whereas the slab model has employed pseudopotentials within the density functional formalism. Using a variety of criteria, we conclude that the bond is strong and ionic with negligible covalent effects. At the monolayer coverage, the charge from the adsorbed potassium atoms is transferred into the empty, antibonding dangling bond surface states resulting in the metallization of the Si(001) substrate surface. The presence of the dangling bond states prevents the alkali monolayer from metallization.