Hydrothermal Synthesis Tungsten Oxide Nanorods/Porous Silicon Composite Structure Gas Sensors

With the continuous development of industrialization,air pollution has become more and more serious.There are a large number of toxic and harmful gases are emitted into the atmosphere every day.These gases will cause serious damage to human health and environmental protection.Nitrogen dioxide?NO₂?is a highly harmful atmospheric pollutant.Therefore,the fast and reliable detection of NO₂ gas at low temperature is very important for both human health and environmental protection.So far,a variety of gas sensitive materials have been found.Among of them,the low-dimensional tungsten oxide nanomaterial has been considered as a promising NO₂-sensing material because of low cost,high sensitivity and so on.Besides,porous silicon?PS?is a new type sensitive material which can work in room temperature,and it is compatible with the integrated circuit.Based on the above background,we want to prepare a new gas sensor based on one-dimensional tungsten oxide nanomaterial/porous silicon composites in order to improve gas-sensing properties and low power consumption.Well-ordered one-dimensional single crystalline WO₃ nanorods were synthesized directly on the porous silicon substrates by a seed-induced hydrothermal method.And the influences of the colloid concentration,the annealing temperature of WO₃ seed layers and the pH value on the morphologies of tungsten oxide nanorods/porous silicon composites were investigated by field emission scanning electron microscope?FESEM?,X-ray diffraction?XRD?and transmission electron microscopy?TEM?.The gas-sensing properties of the sensor based on tungsten oxide nanorods/porous silicon composites were investigated.It reveals that the WO₃ nanorods are generally vertical to the PS substrate and the pores of PS also grow a large number of WO₃ nanorods until the bottom of the pores at the optimal conditions.The diameters and lengths of WO₃ nanorods,which were hexagonal phase,were 25-80 nm and 600-700 nm,respectively.And there are large amounts of oxygen vacancies in there WO₃ nanorods.The sensor based on WO₃ nanorods/porous silicon composites exhibit a high response,excellent selectivity and good repeatability at room temperature.However,the preparation of WO₃ nanorods/porous silicon composites is complicated,and the aspect ratio of WO₃ nanorods is not large enough.In order to improve the aspect ratio of WO₃ nanowires,WO₃ nanowires/porous silicon composites were also prepared by a simple hydrothermal method in this paper,and ammonium sulfate was used as inducer.Dense and uniformly distributed WO₃ nanowires,which were hexagonal phase,were completely contained on the surface and the pores of PS.The diameters of WO₃ nanowires were 30-40 nm,and the lengths of WO₃ nanowires were larger than 2 ?m.This study is significant for further improve the gas-sensing properties of the sensor based on WO₃ nanowires/porous silicon composites.