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Nanotube-based ionization gas sensors
A carbon-nanotube-based ionization gas sensor has been demonstrated by researchers at Rensselaer Polytechnic Institute [Nature, 424, 171 (2003)]. The design offers advantages over other types of gas sensors and may lead to inexpensive systems for environmental monitoring. Nanotube gas sensing has been reported previously, but those sensors rely on changes in electrical conductance as the basis of detection. Electrical-conductance sensing can be used to detect some gases efficiently, but the method is affected by environmental conditions, such as changes in humidity and temperature. In addition, the technique is difficult to apply to gas mixtures and to gases that exhibit unfavorable gas-nanotube interactions. To avoid these problems, Ashish Modi, Nikhil Koratkar, Pulickel M. Ajayan, and their coworkers designed a detector in which ionization characteristics provide a fingerprint for gas identification, even in gas mixtures. The team explains that the method takes advantage of the extreme sharpness of nanotube tips to generate very high electric fields at voltages that are much lower than those applied to conventional electrodes
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