Growth of ZnO nanorods by air annealing of ZnO films with an applied electric field

A novel method of ZnO nanorods growth is presented based on low temperature (300 °C) air annealing of ZnO film while applying an electric field (∼ 10 V/cm) parallel to the film. The films were deposited on glass substrates using a filtered vacuum arc deposition system equipped with a Zn cathode, at an arc current of 160 A, oxygen pressure of 3.2 mTorr, and deposition time of 30 s. Cu tape electrodes were applied on each end of the coated sample, and used to apply the electric field. The samples were annealed in a quartz furnace at 200, 300, 400 °C for 20 or 60 min. Each sample surface was examined using a Scanning Electron Microscope (SEM) and a High Resolution SEM (HRSEM) to study its micro- and nano-structure. The film crystallographic structure was studied using X-ray diffractometry (XRD). ZnO rods with lengths of ∼ 3 μm were observed on the samples annealed at 300 °C for 20 min with an electric field of ∼ 10³ V/m, while separated conical forms with lengths of ∼ 0.5 μm and base width of ∼ 150 nm were observed after annealing under the same conditions but without any electric field. The rod growth rate and area density were ∼ 2.0-2.5 nm/s, and ∼ 3 × 10⁷ cm^{- 2}, respectively.