NiO films consisting of vertically aligned cone-shaped NiO rods

Abstract

By thermally heating a nickel foil in a vacuum of ∼5×10−2Torr, films consisting of vertically aligned cone-shaped NiO microrods were deposited on Si (001) substrates at a temperature of <300°C. The NiO rods were grown along ⟨001⟩ directions by stacking the NiO (001) nanoslices, and are ∼10μm long with a sharp nanosized tip. Due to this morphology, the NiO film exhibited a threshold field of ∼6.5V∕μm in field emission and a field enhancement factor of 2130 that is sufficiently high for field emission applications. The optical band gap of the NiO film was estimated to be ∼3.68eV from the optical absorption measurement and was almost a constant upon heating. In addition, the NiO film exhibited a strong photoluminescence at ∼674nm when excited by a 514 nm Ar+ laser, which might be attributed to the oxygen vacancies.