Structure of the K/Si(100)-(2×1) surface: Semiempirical self-consistent-field crystal orbital analysis

The electronic structure of the K/Si(100)-(2×{}1) surface at a K coverage {Θ}=0.5 has been studied by a semiempirical self-consistent-field Hartree-Fock crystal orbital (CO) formalism supplemented by an INDO (intermediate neglect of differential overlap) Hamiltonian. A symmetric dimer model has been used to represent the structure of the Si(100)-(2×{}1) surface. Four possible adsorption sites for the K atoms have been investigated. The relative stabilities of the adsorption sites have been determined by total energy calculations. The Si(100)-(2×{}1) surface covered with chemisorbed K atoms is stabilized by multicenter Si-K bonding, which favors K adsorption at surface sites where the coordination to the Si atoms is maximized. The charge transfer from the K overlayer to the Si substrate indicates that the nature of the Si-K bonding is partially ionic. At a K coverage {Θ}=0.5 the K/Si(100)-(2×{}1) system is metallic. The charge carriers at the Fermi level are located at the outermost Si layer. The semiconducting Si(100)-(2×{}1) surface is, therefore, metallized upon deposition of K atoms.