Growth mechanism and properties of ZnO nanorods synthesized by plasma-enhanced chemical vapor deposition

Abstract

Uniformly distributed ZnO nanorods have been grown by plasma-enhanced chemical vapor deposition using a two-step process. By controlling the oxygen content in the gas mixture during the nucleation and growth steps, no catalyst is required for the formation of ZnO nanorods. High-resolution transmission electron microscopy studies show that ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. Alignment of these nanorods with respect to the substrates depends on the lattice mismatch between ZnO and the substrate, the surface electric field, and the amount of defects in the starting nuclei. Room-temperature photoluminescence measurements of these ZnO nanorods have shown ultraviolet peaks at 380 nm with a full width at half-maximum of 106 meV, which are comparable to those found in high-quality ZnO films. Photoluminescence measurements of annealed ZnO nanorods in hydrogen and oxygen atmospheres indicate that the origins of green emission are oxygen vacancies and zinc interstitials, while oxygen interstitials are responsible for the orange-red emission. A mechanism for the nanorod growth is proposed.