Characterization of ZnO needle-shaped nanostructures grown on NiO catalyst-coated Si substrates

ZnO nanostructures were synthesized over NiO-coated Si substrate by a thermal evaporation of Zn powders in a vertical chemical vapor deposition (CVD) reactor. The ZnO nanostructures had a needle-like morphology and the diameter of the structures decreased linearly from the bottom to the top. The bottom diameters of the ZnO nano-needles normally ranged from 20 to 100 nm and the lengths were in the range of 2-3 mum. The clear lattice fringes in HRTEM image indicated the growth of good quality hexagonal single-crystal ZnO. Field emission (FE) characteristics of the ZnO nano-needles showed that the turn-on field was about 8.87 V/mum with a field enhancement factor of about 1099. The growth mechanism of the ZnO nano-needles was proposed on the basis of experimental data. (C) 2004 Elsevier B.V. All rights reserved.