The Humidity Sensing Properties Of The LnFeO₃,MoS₂ And SmFeO₃@MoS₂ Heterostructure

Humidity sensor,one of the most important devices in our daily life,has been widely applied to numerous fields,including home automation,civil engineering,monitoring human breath,smart devices and so on.Recently,the humidity sensor with high responsivity,low cost and excellent long-term stability has attracted much attention.The main research contents are summarized as follows:1.LnFeO3(Ln = Sm,Nd,La)nano fibers are synthesized by electrospinning and characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM)and X-ray photoelectron spectroscopy(XPS).The humidity sensors based on LnFeO3 nano fibers are fabricated and measured at different relative humidity(RH)range from 11%to 95%at room temperature.At the whole RH,the optimal working frequency of LnFeO3 nanofibers humidity sensors are all 100 Hz at which the humidity sensors are of good linearity and high response.Compared with other humidity sensors,SmFeO3 nano fibers humidity sensor shows the best sensitivity,and the impedance variation is more than five orders of magnitude within the whole humidity range.The response time of SmFeO3 nano fibers humidity sensor is about 10 s and the impedance versus RH curve is of good linearity(R-square=0.98).The results indicate that the SmFeO3 nano fibers which are of low Ln-0 binding energy exhibit the best humidity sensing properties compared with other LnFeO3 nano fibers.2.The MoS2 nano flowers are synthesized by the hydrothermal method and its crystal structure and surface morphologies are characterized by XRD and TEM.The corresponding humidity sensor is fabricated to investigate its humidity sensing properties.The results show that the impedance variation of the humidity sensor is almost four orders of magnitude when the humidity changes from 11%to 95%RH at low frequencies(10-1000 Hz).The response time of the MoS2 nano flowers humidity sensor is only about 1 s.Furthermore,the humidity sensor is of good repeatability at the measurement of the response characterizations and mouth respiration.The fast response speed of the humidity sensor is ascribed to the property of water molecules physisorption on the surface of the MoS2 nano flowers.3.The SmFeO3-modified MoS2(SmFeO3@MoS2)nanocomposites are successfully synthesized by the hydrothermal method combining with electro spinning.The SmFeO3,MoS2 and SmFeO3@MoS2 are characterized by the XRD,TEM and XPS,and fabricated into humidity sensors to investigate their humidity sensing properties.The results show as follows:At 10 Hz,the impedance variation of the SmFeO3@MoS2 humidity sensor is more than five orders of magnitude within the whole relative humidity(RH)range of 11%to 95%RH,100 times higher than that of the MoS2 humidity sensor(three orders of magnitude).The response and recovery times of the SmFeO3@MoS2 humidity sensor are 1.5 s and 29.8 s,which are greatly shorter than that of the SmFeO3 humidity sensor(10 s and 180s).The maximum hesteresis of the SmFeO3@MoS2 humidity sensor is less than 2%RH.The enhanced humidity sensing properties of SmFeO3@MoS2,which are superior to that of SmFeO3 and MoS2,are ascribed to the synergistic effect between SmFeO3 and MoS2.