Development of WO3 nanostructure by acid treatment and annealing

Tungsten oxide (WO3) nanostructure is an interesting material for many applications such as batteries, gas sensors, photocatalysts, display utilizing, and smart windows. In this work, we fabricated the WO3 nanoplates by sputtering, acid treatment and annealing. Firstly, a tungsten film was deposited on a silicon or glass substrate by sputtering. The film was then immersed in nitric acid (HNO3) at 80 °C. The effect of the exposure time, and annealing temperature was investigated. After the acid treatment, the tungsten oxide hydrate or tungstile (WO3•H2O) with nanoplate structure was developed. The optical transmittance in the visible range was significantly improved compared to the continuous tungsten film. The size of the nanoplate was found to increase with increasing the immersion time. The tungsten oxide hydrate nanoplates transformed into WO3 after annealing at ≥ 200 °C. Increasing annealing temperature resulted in the decreasing size of the nanoplates. The shape of the nanoplates became more of the rectangular shape with annealing. The optical transmittance of the WO3 film increased with the annealing temperature up to 400 °C.