Synthesis of the cactus-like silicon nanowires/tungsten oxide nanowires composite for room-temperature NO2 gas sensor

Abstract

In the present work, the tungsten oxide (WO3) nanowires functionalized silicon nanowires (SiNWs) with cactus-like structure has been successfully synthesized for room-temperature NO2 detection. The novel nanocomposite was fabricated by metal-assisted chemical etching (MACE) and thermal annealing of tungsten film. The WO3 nanowires were evenly distributed from the upper to the lower part of the SiNWs, indicating excellent uniformity which is conducive to adsorption and desorption of gas molecules. The gas-sensing properties have been examined by measuring the resistance change towards 0.25–5 ppm NO2 gas. At room temperature, which is the optimum working temperature, the SiNWs/WO3 nanowires composite showed two-times higher NO2 response than that of the bare SiNWs at 2 ppm NO2. On the contrary, the responses of composite sensors to high concentrations of other reducing gases were very low, indicating excellent selectivity. Simultaneously, the composite sensors exhibited good sensing repeatability and stability. The enhancement in gas sensing properties may be attributed to the change in width of the space charge region, which is similar to the behavior of p-n junctions under forward bias, in the high-density p-n heterojunction structure formed between SiNWs and WO3 nanowires.