Preparation And Characterization Of The Ammonia-sensitive Film Study

Gas sensitive materials and gas sensors have been widely used in the design of electronic nose and electronic tongue of bionic systems. They have many potential applications in food industry, environmental monitoring, anti-terrorism, the inspection of drugs and toxic gases, and the prognoses of some diseases. It is important to study the sensors consisted of organic films with high sensitivity, rapid response and good reproducibility and research the relationship among the materials, technologies and properties of devices, which is helpful in exploring the rules in these kinds of gas sensors to conduct the design, development and applications of new materials and new devices.The progress of gas sensors was reviewed in this paper, and the influence factors and approaches to improve gas sensitivity were also analyzed. Aiming at high sensitivity, fast response rate, reproducibility and reversibility at room temperature, we have made some research in sensitive materials and film processing techniques.First, the selection of sensitive materials was discussed. As the organic sensitive materials and the organic-inorganic composite materials have many advantages, they become the research hot topics. Three sensitive materials such as 3, 4-polyethylenedioxythiophene (PEDT), polypyrrole (PPy), PPy-TiO₂ were prepared via in-situ chemical oxidation polymerization.PEDT was synthesized using chemical oxidation method. The film was characterized by infrared (IR) spectrophy and scanning electron microscope (SEM). Some factors affecting the properties of PEDT film were studied. Chemical field-effect transistor (ChemFET) gas sensor had been fabricated with the obtained PEDT film. The ammonia (NH₃) gas-sensitive characteristics and the drain current variation caused by the temperature and humidity were investigated. The results show that PEDT film is sensitive to NH₃.PPy and PPy-TiO₂ thin films were also prepared by in-situ chemical oxidation polymerization and electrostatic self-assembly combined technique. The films were characterized by UV-Vis absorption spectrum, IR and atomic force microscopy. With the assistance of interdigitated electrodes, gas sensors using PPy, PPy-TiO₂ composite thin films were achieved, respectively. The sensitivity of the sensors to toxic gase NH₃ and the resistance changes induced by the temperature and humidity were investigated. The results show that the PPy-TiO₂ film sensor is less sensitive to NH₃ than PPy film sensor, but its response-recovery time becomes shorter, its temperature and humidity properties and its stability have been improved a lot.The result in this dissertation would be beneficial for the further study of gas sensors composed of polymer films and their composite films.