Metallicity of atomic wires§

The variety of atomic ‘‘dimensional’’ wires can now be synthesized on furrowed and stepped surfaces. These adlayers provide a variety of opportunities for systematically tailoring the surface properties. One of key issue is the metallicity of an atomic wire (even a ‘‘supported’’ atomic wire). Monte-Carlo simulations provide insight into the parameters of indirect interaction that are the basis for the formation of the atomic wires and their stability. In some cases, these results can be directly compared with density functional theory (DFT) calculations of energies of the lateral interactions between adsorbed atoms—one of the most transparent example of Sr/Mo(1 1 2) is presented here as well. It is the surface band structure calculations that provide insights on how metallicity in such surface structures might be altered. Surprisingly, like most of ‘‘metallic’’ wires on semiconductor surfaces, linear chains of alkaline earth on the furrowed transition metal surfaces, such as the Mo(1 1 2) surface, also do not exhibit strong metallic character but, rather, may be considered dielectric atomic chains. The adsorption bonds result in a loss in electron itinerancy, leading to greater valence electron localization in the adlayer in some cases. The localized character of the bands near the Fermi level, associated with the adlayer, is replaced by a metallic band structure when the lattice period of the adsorbed layer becomes incommensurate with the substrate periodicity along the furrows with increasing coverage of the adlayer. With changes in adlayer coverage, both theory and experiment indicate that the adsorbed layers can undergo a Wilson type nonmetal-to-metal transition.