Low temperature thermal oxidation synthesis of ZnO nanoneedles and the growth mechanism

This paper introduced a novel and simple process for synthesizing one-dimensional ZnO nanoneedles at a relatively low temperature in the air. The morphologies and microstructures of the plated Zn nanocrystallines and ZnO nanoneedles were characterized by using SEM, TEM, HRTEM and XRD techniques. The results revealed that: (1) the ZnO nanoneedle exhibited a clean surface and circular cross-section with a diameter of 20–80 nm at the root, 20 nm at the tip and length up to 5 μm, which was different from the other well-accepted synthesis process such as CVD; (2) the optimal synthesizing temperature was between 300 °C and 400 °C; (3) the nanoneedles grew vertically from the metal substrate along the close-packed hexagonal 〈0 0 0 1〉 direction; (4) the Zn nanocrystalline overlayer and ZnO piezoelectric property played key roles for the flourishing growth of the nanoneedle due to its high surface activity and providing large driving force; (5) Comparing with the regular vapor–liquid–solid (V–L–S) or V–S mechanism, a novel growth mechanism “solid state base-up diffusion model” was proposed.