Hydrogen and oxygen adsorption on ZnO nanowires : A first-principles study

We employ first-principles calculations to investigate the structural stability and electronic properties of zinc oxide (ZnO) nanowires adsorbed with different chemical functional groups. The nanowires with one hydrogen monolayer on the surfaces adsorbed with both O and Zn atoms maintain their bulklike geometries, whereas the surface relaxation is found to be significant for the bare and partially adsorbed nanowires. While a half monolayer coverage of hydrogen on an oxygen-adsorbed surface induces metallic behavior, the adsorption of a full monolayer removes the states from the band gap to render a system with a well-defined band gap, revising previous theoretical predictions of metallicity in the latter. On the other hand, when all surface atoms are saturated, either with hydrogen atoms only or with both OH and H groups, the semiconducting behavior is recovered. Our results open up the possibility of tailoring the electronic properties by controlling the surface adsorption sites.