Catalytic growth and characterization of ZnO nano-needles

ZnO nanostructures were synthesized at 500°C over nickel catalyst supported on Si substrate in a homemade vertical chemical vapor deposition (CVD) reactor. The ZnO nanostructures had a needle-like morphology that the diameter of structures decreased linearly from the bottom to the top. The diameters of the ZnO nano-needles normally ranged from 20-100 nm and the lengths were in the range of 2-3 μm. The nano-needles had a single wurtzite structure. The clear lattice fringes in HRTEM image also revealed the growth of good quality hexagonal single-crystal ZnO. The photoluminescence (PL) spectra of the nano-needles excited with a ultra-violet (UV) emission of 3.3 eV and a weak green emission at 2.4 eV at room temperature. Field emission characteristics of the ZnO nanowires showed that the turn-on field of ZnO nanowires was ∼6.10 V/μm with a field enhancing factor β of ∼1099. The catalytic growth mechanism of the ZnO nanowires was discussed on the basis of experimental results in this work.