| Humidity is a physical quantity that represents the drought-wet degree of atmospheric, and it is closely related to human life and national production. The environmental humidity has a great influence on human health, and it also has deep influence on industrial and agricultural production, meteorology, environment protection, aerospace, national defense and other fields. With the development of science and technology, the demand for humidity sensor with high performance is increasing. Therefore, it is very important to develop the humidity sensor which has high sensitivity, fast response, small hysteresis and low cost. In this dissertation the quartz crystal microbalance(QCM) was chosen as sensing device, and humidity sensors with polyethyleneimine/graphene oxide(PEI/GO) self assenbled films and graphene oxide/zinc oxide(GO/ZnO) layered thin films were prepared. The sensitive films were characterized and the humidity sensing properties of sensors at room temperature within 11.3-97.3%RH humidity range were systematically studied. This paper mainly includes the following two parts:(1) PEI/GO humidity sensitive films were deposited on QCM devices by using electrostatic layer-by-layer(LBL) self-assembly technic. The effect of the structure and the number of layers on sensing properties of QCM humidity sensor at room temperature was studied. The results showed that the humidity sensor possessed good humidity-sensing properties when PEI was the uppermost layer. The response value increased with the increase of layer numbers and the maximum response was 1802 Hz. While the hysteresis first decreased and then increased with the increase of layer numbers and the minimum hysteresis is 4.2% RH. In addition, the humidity sensing properties of PEI/single layer graphene oxide(SGO) self-assembled films were preliminarily explored. The maximum response of PEI/SGO QCM humidity sensor with 9 layers was 3338 Hz. But there was no significant change in response/recovery times and hystereses when compared with PEI/GO sensor. The humidity sensing mechanism model was established combined with scanning electron microscopy(SEM), UV-Vis absorption spetrum and fourier transform infrared spectrum(FTIR). The infrared spectrum showed that there was an amide reaction between PEI and GO. It was suggested that self assembled films contained more hydrophilic groups, and water molecules were adsorbed on the film mainly by physical adsorption.(2) GO/ZnO layered films were deposited on the QCM device by spraying process. The sensing properties of the sensor were tested, and the effect of film structure on sensing properties of QCM humidity sensor was studied. The results showed that the sensing performance of GO/ZnO( in which ZnO film was the lower layer) was superior than ZnO/GO(in which ZnO film was the upper layer). The GO/ZnO-QCM humidity sensor had a sensitivity of 41.1 Hz/%RH, the minimum response/recovery time reached 2s/3s, and its repeatability and stability were also good. It was believed that ZnO nano particles in the GO/ZnO film played a supporting role in the GO layer, and the size of ZnO particles in the layered films was smaller than that of single ZnO, leading to an increased specific surface area and more adsorption sites of GO/ZnO layered thin films. Thus the humidity sensing characteristics GO/ZnO layered film was improved. The humidity sensing properties of SGO/ZnO layered thin films were also preliminarily explored. It was found that the response of SGO/ZnO humidity sensor increased significantly compared with GO/ZnO, and the hysteresis was decreased. It was believed that SGO provided more water molecules adsorption sites than GO. |
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