Atom-selective loss structures: evidence for semiconducting property of Na/Si(1 0 0) surfaces

We report why Na adsorption on the Si(1 0 0) surface leads to satellites in photoemission spectra at room temperature. Adsorbate-related peaks, Na 2p and Na LVV, lose their kinetic energy by about 2.0 eV, while a satellite is found at a loss energy of about 3.0 eV. In contrast to previous reports, we ascribe the loss structures as being due to atom-selective interband transitions. The satellites are suggested as evidence for the semiconducting nature rather than for the metallic character of the Na/Si(1 0 0) surface.