Tuning the Conductivity of Metallic Nanowires by Hydrogen Adsorption

Nearly one-dimensional metallic nanowires can be grown by Au deposition on semiconducting substrates. Although the wires are basically decoupled from the substrate, their conductivity can be tuned by modifications of the environment, such as the adsorption of foreign species. In this work, we present a detailed theoretical investigation of the metallicity modifications in a system consisting of self-assembled Au atomic wires on a stepped Si(557) surface upon hydrogenation. Our first-principles calculations within density functional theory (DFT) reveal chemically different favorable adsorption sites of similar energy for H. The H adsorption at all sites leads to strong modifications in the electronic structure, due to the adsorbate-to-substrate charge transfer. Interestingly, the whole electronic system, including the Au related electronic states, is modified by H adsorption, without direct interactions of H and the Au chains. Changes in band order as well as a band gap opening nicely explain recent plasmon spectroscopy experiments.