Preparation And Sensing Properties Of Si Nanowires/WO₃ Nanowires Composite Array

NO₂ is virulent gas,which could harm the environment and human health.NO₂contaminates the atmosphere,the water and the soil,and furthermore causes the phenomena of acid rain,the water acidification.Meanwhile,the toxicity of NO₂ may tremendously do damage to the human health,and induce the respiratory illnesses,like the pulmonary edema.The concentration of NO₂ in atmosphere should be lower than 106 ppb,according to China's regulations,and therefore it is crying needs to develop a NO₂ gas sensor with high performance,which could realize the rapid,accurate and reliable detection of NO₂ in the field of NO₂ gas sensing.There is a popular believe that the tungsten oxide nano-structures and the silicon nanowires?SiNWs?are promising gas sensing materials.Researches show that,the application of heterojunctions in gas sensitive area,may dramatically improve the performance of gas sensors,that is,the heterostructure formed by the recombination of SiNWs and tungsten oxide nanowires may be a potential research orientation in the future.In this paper,the aligned SiNWs substrates were prepared by metal assisted chemical etching?MACE?and KOH second etching method,the tungsten films were fabricated by magnetic sputtering,followed by the thermal oxidization of tungsten films and the hydrothermal growth of SiNWs array,and finally the heterojunction structure synthesized with tungsten oxide nanowires on SiNWs array.Though modulating the morphology of the composite structure,the working temperature of the gas sensor notably decreases and the gas sensing properties are improved.The experiment results suggest that the dendritic and homogeneous brush-like SiNWs/tungsten oxide nanowires composite structures,which were fabricated by the thermal oxidizing of tungsten films,present an excellent NO₂ gas sensing characteristics.At room temperature,exposed to 5 ppm NO₂,the two composite structures show the NO₂ responses of 11.9 and 21.0,respectively,which are 4 times and 7.2 times higher than that of pure SiNWs?2.9?,he response times are all less than 1s,and the recovery time are 11s and 20s,respectively.In addition,the two composite structures all present outstanding repeatability and selectivity.Meanwhile,the gas sensing mechanism of composite sensor is also illustrated,and the improvement of the gas sensing properties could be benefit from the following factors:a mass of heterojunctions at the interfaces formed by the recombination of SiNWs and tungsten oxide nanowires,the extra conductive paths caused by the connections between the tungsten oxide nanowires on adjacent SiNWs and the array structure of vertical,aligned SiNWs.