Synthesis and low-temperature gas sensing properties of tungsten oxide nanowires/porous silicon composite

A novel tungsten oxide nanowires/porous silicon composite has been successfully synthesized via a convenient thermal evaporation method with no catalyst. The morphology and crystal structure of products obtained were investigated by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The diameters and lengths of nanowires were 40-60 nm and 20-30 μm, respectively, and the aspect ratio (length/diameter) of nanowires can be in range of 500-750. The factor influenced the morphology was substrate temperature. The diameter of nanowires decreased as the substrate temperature increased. The sensor made of tungsten oxide nanowires/porous silicon composite exhibited a high response (∼3.32), fast response/recovery (∼175/44 s) and excellent selectivity toward 2 ppm NO2 at a low operating temperature of 100 °C. Modulations of the depletion width along the nanowires are likely to be the reasons for the low-temperature gas sensing properties. Furthermore, modulations of the potential barriers at both networked nanowires homojunctions and heterojunctions between porous silicon and tungsten oxide are also responsible for the good gas sensing properties at a low operating temperature.