Controlled synthesis of carbon nanostructures using aligned ZnO nanorods as templates

By combining in situ X-ray photoemission spectroscopy, ex situ high resolution transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy, we show that chemical vapor deposition (CVD) on vertically aligned ZnO nanorods can synthesize different carbon nanostructures (CNs), whose morphology is driven by the ZnO nanorods and whose dimensions and structures change as a function of the process temperature. The CNs range from amorphous carbon cups, completely covering the nanorods, to high density one-dimensional carbon nano-dendrites (CNDs), which start to appear like short hairs on the ZnO nanorods. The nanorods are partially etched when the process is done at 630-800 C, while they are completely etched at temperatures higher than 800 C. In the latter case, CNDs emerge from a porous carbon sponge formed at the substrate interface but they are preferentially aligned along the location of the pristine ZnO nanorods. When used as a chemiresisitor the CND-ZnO structures have a higher sensitivity to ammonia compared to chemiresistors made by bare ZnO nanorods, to other one-dimensional CNs, like carbon nanotubes or other metal/metal-oxides hybrid CNs.