From copper nanocrystalline to CuO nanoneedle array: Synthesis, growth mechanism, and properties

In the present work, a novel method for synthesizing a one-dimensional CuO nanoneedle array was introduced; that is, first, a pure copper nanocrystalline layer was plated by using a periodic reverse pulse plating process, and then the CuO nanoneedle array grew upon the layer through thermal oxidation in the air. The nanocrystalline layer and nanoneedles were characterized by using scanning electron microscopy, regular and high-resolution transmission electron microscopies, X-ray diffraction, X-ray photoelectron spectroscopy, and a thermal analysis system (thermogravimetry and differential scanning calorimetry). The results showed that the oxidation temperature and the Cu2O intermediate phase played key roles for growing CuO nanoneedles. A self-catalyzed based-up diffusion model was proposed for interpreting the nanoneedles' growth mechanism. The field emission property of the nanoneedles showed that the electron emission turn-on field is about 0.5 V mu m(-1) at current density 10 mu A cm(-2), and the maximum current density is 2.5 mA cm(-2) with a linear F-N relationship. The full Sun efficiency (eta) of the CuO nanoneedle used as a cathode in dye-sensitized solar cells is 1.12%, which shows it to be a potential material in solar cells.