Gold as an intruder in ZnO nanowiresElectronic supplementary information (ESI) available: Schematic representation of bond angles. The HOMO and LUMO for Au interstitials: thread and point defects. See DOI: 10.1039/c5cp01415h

Several techniques for obtaining ZnO nanowires (ZnO NWs) have been reported in the literature. In particular, vapour-liquid-solid (VLS) with Au as a catalyst is widely used. During this process, Au impurities in the ZnO NWs can be incorporated accidentally, and for this reason we named these impurities as intruders. It is thought that these intruders may produce interesting alterations in the electronic characteristics of nanowires. In the experiment, it is not easy to detect either Au atoms in these nanowires, or the modification that intruders produce in different electrical, optical and other properties. For this reason, in this density functional theory investigation, the effect of Au intruders on ZnO NWs is analysed. Au extended (thread) and point defects (atoms replacing Zn or O, or Au interstitials) are used to simulate the presence of gold atoms. Optimised geometries, band-gaps and density of states indicate that the presence of small amounts of Au drastically modifies the electronic states of ZnO NWs. The results reported here clearly indicate that small amounts of Au have a strong impact on the electronic properties of ZnO NWs, introducing states in the band edges that may promote transitions in the visible spectral region. The presence of Au as an intruder in ZnO NWs enhances the potential use of this system for photonic and photovoltaic applications. In the vapour-liquid-solid technique with Au as a catalyst (widely used to obtain ZnO nanowires), Au intruders can be incorporated accidentally. In this theoretical investigation we report that Au as an intruder in ZnO nanowires enhances their potential use for photonic and photovoltaic applications.