SHAPE EVOLUTION IN ONE-DIMENSIONAL ZnO NANOSTRUCTURES GROWN FROM ZnO NANOPOWDER SOURCE: VAPOR–LIQUID–SOLID VERSUS VAPOR–SOLID GROWTH MECHANISMS

Here we report on the growth and evolution of ZnO nanowires grown from ZnO nanopowder as a source material using a horizontal muffle furnace. The shape evolution has been studied with variation in growth temperature and zinc vapor pressure. The structural analysis on these nanostructures shows c-axis oriented aligned growth. Scanning electron microscopy imaging of these nanostructures revealed the shape evolution from nanowires to nanoribbons and then to nanorods as the growth temperature increases from 650°C to 870°C. At 650°C, only vertical nanowires have been observed and with increase in growth temperature nanowires transform to nanoribbons and then to nanorods at 870°C. And we also observed simultaneous growth of nanorods and nanoribbons under a specific growth condition. We believe that these nanowires and nanorods were formed by vapor–liquid–solid growth mechanism (catalyst-mediated growth), whereas nanoribbons were grown by vapor–solid growth mechanism (without the aid of a metal catalyst). We observed simultaneous occurrence of vapor–liquid–solid and vapor–solid growth mechanisms at a particular growth temperature. These ZnO nanowires exhibit bound exciton related UV emission at ~379 nm, and defect-emission band in the visible region. Possible growth mechanism, shape evolution, and simultaneous growth of two types of one-dimensional ZnO nanostructures under the same growth condition are discussed.