Growth and field-emission properties of single-crystalline conic ZnO nanotubes

Abstract

Single-crystalline conic ZnO nanotubes were synthesized on Si(001) without catalysts by thermal chemical vapour deposition at 475 °C. The nanotubes grown along the ZnO [0001] direction are sharp open-ended tips consisting of planar defects revealed by transmission electron microscopy and scanning electron microscopy. The nanotubes were formed by self-assembly of numerous six-radiated branches of hexagram nanosheets. The diameters and the wall thicknesses of the nanotubes are in the ranges 30–100 and 15–30 nm, respectively. The lengths and areal densities of the nanotubes are around 0.5 µm and 1–9 × 108 cm−2, respectively. Field-emission measurements on the conic nanotubes show a low turn-on field of 3.5 V µm−1 at 10 µA cm−2. The field-emission properties related to the nanotube density and geometry and the nonlinearity in the Fowler–Nordheim (FN) plot at lower field region are discussed.