Eutectic condensation and nucleation in vapor-liquid-solid grown ZnO nanorod arrays on Si substrate

It is very important to understand the growth mechanism of ZnO nanostructures for control of the morphologies and further design of optoelectronic devices. In this paper, the eutectic condensation of Zn vapor and catalyst Au, nucleation and epitaxy of ZnO nanorods were intuitionally observed in chemical vapor deposition process by controlling the temperature and atmosphere. The vertically aligned ZnO nanorod arrays were fabricated on Au-coated Si substrate. A Zn-riched buffer layer was found on Si substrate. Under the atmosphere nearly without O2, it was clearly observed that the nano-sized sprouts appeared on the buffer layer and Au-Zn condensed bigger and bigger with increase of temperature. When the O2 was introduced, the as-grown nanorods almost kept the same size and density with those sprouts grown at the same temperature without O2. The morphologies and composition analysis provided direct evidence for a bottom-catalyzed vapor-liquid-solid mechanism of ZnO nanorod arrays on the lattice-mismatched substrate.