Growth of hexagonal tungsten trioxide tubes

A simple approach to fabricating tungsten trioxide tubes was developed. Tungsten wires were heated at around 800 °C in a humid argon flow and hexagon-shaped tubes with well faceted end and side surfaces resulted. As observed with a scanning electron microscope (SEM), the tubes were about 1 μm in cross-sectional dimension and 10 μm in length. The selected-area electron diffraction (SAED) pattern obtained in the transmission electron microscopy (TEM) study revealed that the tubes were hexagonal tungsten trioxide (h-WO3) crystals. The formation of the well-faceted tubular structure is attributed to the lateral coalescence of WO3 nanowires accompanied with a dehydration process.