Synthesis of tungsten oxide tapered needles with nanotips

Tungsten oxide tapered needles with nanotips were synthesized on a large scale by reacting tungsten nanopowders with hydrous nickel nitrate in hydrogen atmosphere. The resultant tungsten oxide needles have lengths more than 100 μm, root diameters of several hundred nanometers and tip diameters of several nanometers, showing a perfectly axisymmetric configuration. HRTEM and SAED analyses showed that the synthesized tungsten oxide tapered needles have a single-crystalline structure with growth direction of [0 1 0]. The effects of the experimental conditions (the ratio between tungsten and hydrous nickel nitrate, the size of tungsten powders, and the reaction atmosphere) on the morphology of the products were systematically investigated. It was found that tungsten oxide nanowires, submicro-/micro-whiskers and microtubules could be facilely obtained under different experimental conditions. The unique configuration and the single-crystal structure of the tapered needles may make them a potential candidate for field emitters and probing tips.