The bottom contact heterojunction organic thin film transistors (OTFTs) based on n-type hexadecafluorophthalocyaninatocopper (F16CuPc) and p-type copper phthalocyanine (CuPc) bilayer were developed by the vacuum evaporation, which were applied to detect nitrogen dioxide (NO2). The sensors with different thickness (5nm, 10nm, 15nm and 20nm) of CuPc were prepared to investigate the influence of CuPc film thickness on the properties of devices. The results showed that four parameters including the source-drain current (IDS), grid current (IGS), threshold voltage (VT) and carrier mobility (μ) changed in a few seconds when the sensors were exposed to the atmosphere of NO2. Further more, IDS and IGS presented extremely similar variation trend. So the grid current would be taken as a new parameter to reveal the response characteristic of OTFT gas sensor. By comparison, the device with 15nm CuPc thin film exhibited the optimum electronic and gas sensing properties.
Hydrogen sulfide is a typical toxic, inflammable gas. The detection of H2S is crucial in the areas of oil, natural gas and so on. However, studies on H2S gas sensors at room temperature were seldom reported. In this study, Quartz crystal microbalance (QCM) sensors have been utilized, and PVP film were prepared on the QCM by airbrush method with different airbrush volume for H2S detection. The results showed that the PVP film with airbrush volume 0.2ml exhibited a better sensing response to H2S gas. Besides, sensitive characteristics parameters, i.e. selectivity, stability, linearity and sensitivity of prepared sensors were studied for comparison. The relative sensing mechanism associated with SEM pictures was studied as well.
The detection of formaldehyde is very necessary and important in both industrial and residential environments. In this paper, a novel quartz crystal microbalances (QCM) formaldehyde gas sensor has been successful fabricated based on Polyethylenimine (PEI)-multi-walled carbon nanotubes (MWCNTs) composite films by the spraying process. The morphology of films was analyzed by scanning electron microscope (SEM), and formaldehyde-sensing properties of sensors were investigated. The results showed that the prepared QCM gas sensor exhibited good response and recovery behaviors towards formaldehyde gas in the concentration range of 0-10 ppm at room temperature, which also has the superior repeatability and selectivity. Moreover, the gas-sensing mechanism of sensors was studied.
The pure conducting polymer P3HT film is less sensitive to the formaldehyde (HCHO), and the pure ZnO film needs a high temperature to militate the HCHO, as a result, the P3HT/ZnO composite was fabricated on the organic thin film transistor (OTFT) by spraying to detect the HCHO at room temperature, the electrical properties and sensing properties of all the prepared OTFT devices were measured by Keithley 4200-SCS source measurement unit. What is more, the effect of different P3HT/ZnO composite masses on the response of sensors were tested, all the sensors showed a remarkable response to HCHO, and the optimized composite mass of 1.0ml was obtained. Since most detecting methods for the HCHO vapor require an high temperature, the experiments and results in this paper showed the important significance for the field of HCHO detecting.
In this paper, a novel humidity sensor based on polymer-carbon nanotube composites was prepared and characterized. Two different methods were adopted to fabricate the humidity-sensing film for these sensors. The surface of the films was observed by a scanning electron microscope (SEM). The sensing material made up of poly(ethyleneimine) and multiwall carbon nanotube was sprayed on the interdigitated microelectrode pairs(IDTs). The resistance between the two electrodes was measured at different relative humidity levels at 19°C. The data shows that the resistance increases with the rise of the relative humidity over the range of 5-90% RH and that, the resistance increases almost linearly in the range of 5-71% RH. The response of the sensors to NO2 and NH3 were also examined, and the results reveal that the sensor is not sensitive to both of them.
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