Tungsten oxide nanorods, nanowires, and three-dimensional (3D) nanowire networks have been synthesized just by controlling an oxygen flow rate which was introduced in thermal evaporation. X-ray diffraction (XRD) results show that the crystal structures of the nanostructural film are indexed to WO2, W18O49, and WO3 phases in sequence with the increase in the oxygen flow rate. High-resolution scanning electron microscopy, transmission electron microscopy, and XRD spectroscopy are applied to investigate the formation process of 3D nanowire networks, and the results indicate that the nanorods grow into nanotrees, and then the nanowire networks grow along a preferred orientation from the bottom to the top with the increase in evaporation time. The growth mechanism for complex 3D-WO3 nanowire networks is also discussed in detail.
