Chemical identification of atoms at multicomponent surfaces on an atomic scale:CoSi2(100)

We found a ($\sqrt{2}$×$\sqrt{2}$)R45° surface reconstruction on the plateau of three-dimensional cobalt silicide islands epitaxially grown on Si(100), which has an inhomogeneous occupation of the lattice sites. We combined voltage dependent scanning tunneling microscopy with ab initio electronic structure calculations and resolve the chemical identity of the surface atoms. We found that Co atoms are imaged for bias voltages probing the unoccupied states above +0.5 eV and vice versa, Si atoms are imaged below +0.5 eV, counterintuitive to the simple interpretation based on the electronic structure of bulk Co and Si.