Tower-Like ZnO Nanorod Bundles Grown on Freestanding Diamond Wafers for Electron Field Emission Improvement

Tower-like ZnO nanorod (ZNR) bundles were grown on freestanding diamond (FSD) wafers by a low-temperature hydrothermal method without any catalysts, and the corresponding electron field emission property was investigated. The structural characterizations disclosed that these tower-like bundles were composed of single crystalline ZNRs with hexagonal wurtzite structure. They grew perpendicularly to each crystal planes of the diamond grains. Different hydrothermal reaction times (e.g., 1.5, 3, 6, 8 h) were carried out to investigate the morphology features of ZNRs grown on the growth surface of FSD wafers. The ZNR bundles with a growth time of 6 h showed the highest crystallinity and aspect ratio. Such ZNR bundles/FSD hybrid exhibited a high emission current density of 0.2 mA at an applied field of 11.8 V/μm and a reduced turn-on field of 6.8 V/μm. The field enhancement factor β was calculated to be ~4979 based on the Fowler-Nordheim theory. The geometry and structure of polycrystalline diamond were responsible for the formation of ZNR bundles and the high β-value.