Electronic structure and local interactions on a Si(100)2x1 surface with submonolayer Ba overlayers

The electronic structure and ionization energy for the system Ba/Si(100)2 X 1 have been studied as functions of the submonolayer coverage. It is found that there is an energy gap in the surface states spectrum and that the Ba /Si(100)2 X 1 interface is semiconducting up to 1.5 monolayers of Ba. Two s urface bands induced by Ba adsorption have been detected. The evolution of the spectrum with increasing degree of Ba coverage points to the existence of two nonequivalent "adsorption sites,'' which differ in binding energy by 0.11 eV. The development of the Ba-induced bands is found to terminate at a coverage corresponding to the minimum ionization energy and close to one monolayer. The adsorption bond is shown to have a primarily covalent charac ter. (C) 1998 American Institute of Physics. [S1063-7761(98)01812-5].