Higher-order Sensors for Fast Detection of Gases
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The research is divided into two main parts: the sensing part and the gas delivery part. The reliable chemical information from the chemical sensor requires that the sensitive layer of the sensor exhibits long-term stability. To improve the stability of the sensing layer, camphorsulfonic acid was added to the formic acid. The introduction of photo-irradiation at 254 nm as an additional treatment to the sensing layer was proved to be effective. For gas selectivity of PANI matrix, metal or metal oxide clusters have been incorporated into the matrix. The composite materials of PANI with silver, copper, iron, nickel, palladium and mercury were also prepared and exposed to different gases. The second part of the thesis discusses the gas delivery system to the sensors using the synthetic jet technology. The sniffing functionality was demonstrated using the designed jet cell for operation in the open system. The gas sniffing experiments showed that in the presence of the jet, the response time of the sensor is faster by about two orders of magnitude (20 compared to 1800 seconds). The jet sampling system was applied to continuous monitoring of ammonia gas filter performance using the chemFET array. The jet system collected the gas before and after filtering, and the difference between the two responses was compared to observe the break-through of the filter. It was concluded that the gas sensing system integrated with the gas sampling functionality can be applied to monitor a gas filter performance. The cell was designed so that the impinging jet covers the sensing active area of the array of eight chemFETs. The two-dimensional distribution of the ammonia gas concentrations showed that the jet covers the active sensing area in an effective way so that the sampling volume for sensing is significantly reduced compared with the conventional gas flow cell system. Based on these initial studies shown in this thesis, the proposed gas sniffing system was shown to be effective in realizing fast detections of gases for critical applications of a gas sensor system.