Quartz Crystal Microbalance (QCM) coated with polyetherimide (PEI) by spin coating method was applied for carbon dioxide (CO2) gas detection at room temperature in this study. The experiments were performed in dry and humid air atmospheres, and the results revealed that the prepared CO2 sensor in moisture circumstance exhibited a larger sensing response than that at dry condition. An enhanced sensing response took place for CO2 detection with the existence of water molecules. The effect of different humidity on QCM sensor performances was investigated as well in this paper. A curve, which displayed a proportional relationship between sensing response and water vapor concentration, was obtained. Moreover, the relevant sensing mechanisms were investigated.
In this paper, gas sensor array with micro-well was designed and prepared by Micro Electro-Mechanical Systems (MEMS) technology. The micro-well and interdigital electrodes of sensor array were prepared using photolithography process, reactive ion etching (RIE) process, wet etching and conventional vacuum evaporation. In the manufacture process of the gas sensor array, KOH wet etching process was mainly discussed. The optimum etching processing parameters were as follows: 30 wt% KOH solution at 80 °C, a cooling back-flow device and a magnetic stirrer. The multi-walled carbon nanotubes (MWCNTs)-polyethyleneoxide (PEO) and MWNTs-Polyvinylpyrrolidone (PVP) composite films were utilized as sensitive layers to test gas-sensing properties. Response performances of MWCNTs- PEO and MWNTs-PVP composite films to toluene vapor and methanol vapor at room temperature were investigated. The results revealed that the sensor array showed a larger sensitivity to toluene vapor than to methanol vapor. In addition, the sensing mechanisms were studied as well.
Polyvinylpyrrolidone (PVP)/reduced graphene oxide (RGO) nanocomposites are sprayed on quartz crystal microbalance (QCM) for NO2 sensing. The thin films are characterized by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-VIS). The experimental results reveal that PVP/RGO sensor exhibits higher sensitivity and shorter recovery time than those of PVP. Besides, the response to 20 ppm NO2 is higher than other gases such as CO, CO2 and NH3 even at 100ppm. When the PVP/RGO sensor is exposed to these gases, the good selectivity to NO2 makes the sensor ideal for NO2 detection.
In this paper, Multi-walled carbon nanotubes (MWCNTs)-tin oxide (SnO2) composites were selected as sensing materials to detect NO2 with concentrations ranging from 10 ppm to 50 ppm. Two sensors with different mass fractions of SnO2 and MWCNTs, i.e., 6.7% and 10%, were fabricated by airbrushing the composites on interdigitated electrodes (IDEs). Response performances of both sensors at room temperature were investigated. Results showed that the sensor with mass fraction of 10% exhibited a larger sensing response and a bigger sensitivity than the other one, and a good linearity was observed for both ones. In addition, both sensors had a good selectivity to NO2 in comparison with the other five interfering gases.
In this paper, bottom contact organic thin film transistors (OTFTs) using SiO2 dielectric layer deposited on silicon wafer were fabricated for gas sensors application. Single-walled carbon nanotubes (SWNTs)- polyethylenimine(PEI) bilayer sensitive film was utilized as an active layer to test current-voltage characteristics and gas-sensing properties of the OTFT device. Due to PEI coating, the electronic characteristic of the active layer was turned from p-type (SWNTs film) into n-type (SWNTs-PEI bilayer film). When the gas sensor was exposed to NO2 of different concentrations at room temperature, the source-drain current changed within several minutes at appropriate gate and source-drain voltages. The selectivity and repeatability of gas sensor were investigated as well. The results showed that the gas sensor exhibited outstanding properties to NO2 gas. Moreover, the gas sensing mechanism of the sensitive film associated with the morphology analyzed by scanning electron microscope (SEM) was studied.
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