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 degrees C to 870 degrees C. At 650 degrees C, only vertical nanowires have been observed and with increase in growth temperature nanowires transform to nanoribbons and then to nanorods at 870 degrees 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 similar to 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.