Preparation And Properties Of. Organic Nitrogen Oxides And Ammonia Sensitive Film

The technology of sensor is the mainstay of modern information industry. Gas sensor as a branch of modern sensors plays a crucial role in many fields such as food industry, atmosphere monitoring, vehicle exhaust and harmful gas detection and other aspects. NO2 and NH3 are main pollutant gases in modern life, so it is imperative to detect them rapidly and precisely for protecting the environment and the health of human being.The selection of sensitive materials is discussed at first. As the organic sensitive material is one of hot topic due to their merits, two kinds of materials, polymer and small molecules, are chosen as sensitive material. Herein we employed 3,4-polyethylenedioxythiophene (PEDT) as the polymer material, and tetracyanoquinodimethane (TCNQ) and tin phthalocyanine (SnPc) as small molecules.PEDT was synthesized using chemical oxidation method. Infrared spectrum (IR) and scanning electron microscopy (SEM) were utilized for the characterization of the obtained PEDT material and surface morphology of the PEDT film. The resistance variation induced by temperature and humidity was measured. The results show that PEDT film is sensitive to both NO2 and NH3.In the case of small molecule, the film of TCNQ and SnPc was prepared by thermal vacuum evaporation. The effect of substrate temperature on the surface morphology and the conductance of the thin film has been investigated. The relation between the sensitivity of thin film and temperature of the substrate was described. We also analyzed the influence of substrate temperature, the thickness of organic film and the space between the electrodes on the sensitivity of gas sensor. The results show that TCNQ is both sensitive to NO2 and NH3, but the response time and recovery time are not fast. SnPc is sensitive to NO2 but insensitive to NH3.At last TCNQ and SnPc films as well as poly(metheyl methacrylate) (PMMA) films doped by TCNQ and SnPc were prepared by spin coating method. The influence of different spin speeds on the sensitivity of organic film was studied. The surface morphology of these films was characterized by SEM technology. The results show that TCNQ film is highly sensitive to NH3. The PMMA film doped by SnPc is also highly sensitive to NO2 with fast response speed, but the recovery time gets longer with the increase of gas concentration.