Humidity Sensing Properties Of Nanostructured ZnO Based On Quartz Resonant Sensors

In recent years, the nanostructured materials, especially the nanostructured semiconductors, such as nanowire, nanorods, nanobelts and nanotetrapods, have attracted more and more attention. These semiconductors have some potential applications ranging from optoelectronics to chemical sensors because of its distinctive optical, electronic and chemical properties. The nearly developed nano structured materials and the nano devices will initialize a new technology revolution in the 21st century.In this thesis, the humidity characteristics of nanostructured zinc oxide were studied and the humidity sensors using ZnO as the sensing element were investigated. The results obtained can provide the guidance for the future study of nanostructured sensors. The mainly works and significant results are listed as following:The nanostructured ZnO was synthesized by two kinds of techniques: the flower like ZnO nanowires by thermal evaporation and the nanoparticle ZnO film by Sol-gel. The prepared nano structures were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) to obtain the information on the structural and morphological properties, etc.The first kind of sensors were constructed by coating the ZnO nanowires, prepared by the thermal evaporation, on quartz crystal microbalance (QCM ) surface as the sensing element. Since the ZnO nanowires have the properties like the large specific arear, the good adsorption ability. The combination will lead to the high-performance sensors. The sensor properties, such as the sensitivity, the reproducibility, the stability etc. are studied. The study indicated that the humidity sensor developed has the high sensitivity and the good reproducibility within the humidity level ranging from 30% to 80%RH. The Study showed that the ZnO is a potential sensing material for humidity sensor.The second kind of humidity sensors were constructed by growing the ZnO nanopaticles on the arms of the quartz tuning forks as the sensing element. The ZnO nanoparticles were grown from the Sol-gel precursor. The sensing properties, such as the sensitivity, the reproducibility, the stability and etc were studied. Our study showed that the ZnO nanoparticles also the good sensing material and the sensor based on the ZnO nanoparticles and the QTF are potential for humidity detection.A prototype of wireless sensor was also investigated. ZnO-QCM humidity sensors we developed have the properties like high sensitivity, the fast response time and the digital output. And these make the real-time detection by the wireless sensor possible.The sensor prototype we developed is composed of two parts. Part I consists of the QCM sensor and the RF-transmitter, which can sense the environment and send out the information; Part II are composed of the RF receiver and the PC, which can receive the sensor signals and show or store them on PC. The wireless sensor has the ability to sense the environment and transmit/receive the sensor signals by RF. The distance for the data wireless transmission was 100m indoor and 300m outdoor, respectively. The constructed system has the ability to monitor the pollutants in the harsh environment.