Confined doping on a metallic atomic chain structure.

On Si(111)-(5×2)-Au it is shown that metallic sections of quantum wires between two doping adatoms establish a local electronic structure which is primarily defined by the section length. Such confined doping is a direct consequence of reduced dimensionality and is not observed in higher dimensions. Within a chain segment, the effect of a spatially independent charge-carrier concentration is superimposed by a Coulomb-like interaction due to the positively charged dopants. This offers a natural explanation for the relatively broad photoemission features and the complex appearance in scanning tunneling microscopy and spectroscopy images.