Surface-state scattering by adatoms on noble metals:: Ab initio calculations using the Korringa-Kohn-Rostoker Green function method

When surface-state electrons scatter at perturbations, such as magnetic or nonmagnetic adatoms or clusters on surfaces, an electronic resonance, localized at the adatom site, can develop below the bottom of the surface-state band for both spin channels. In the case of adatoms, these states have been found very recently in scanning tunneling spectroscopy experiments for the Cu(111) and Ag(111) surfaces. Motivated by these experiments, we carried out a systematic theoretical investigation of the electronic structure of these surface states in the presence of magnetic and nonmagnetic atoms on Cu(111). We found that Ca and all 3d adatoms lead to a split-off state at the bottom of the surface band which is, however, not seen for the sp elements Ga and Ge. The situation is completely reversed if the impurities are embedded in the surface: Ga and Ge are able to produce a split-off state whereas the 3d impurities are not. The resonance arises from the s state of the impurities and is explained in terms of strength and the interaction nature (attraction or repulsion) of the perturbing potential.