ZnO nanopencils: Efficient field emitters

ZnO nanopencils were synthesized on a silicon wafer without catalysts at a low temperature of 550° C through a simple two-step pressure controlled thermal evaporation. Penholders were well-hexagonal faceted and the diameter of pen tips on the nanopencils was in the range of 20-30 nm. High-resolution transmission electron microscopy shows that the nanopencils were single crystals growing along the [0001] direction and the pen tips subtend a small angle with multiple surface perturbations. Field-emission measurements on the nanopencils show a low turn-on field of 3.7 V ∕ μ m at a current density of 10 μ A ∕ cm 2 . The emission current density reached 1.3 mA ∕ cm 2 at an applied field of 4.6 V ∕ μ m . The emission at the low field is attributed to the sharp tip and surface perturbations on the nanopencils.