Carbon nanotubes offer path to flexible, low cost sensors

A team from the Technische Universität München (TUM) has demonstrated carbon nanotube based gas sensors fabricated on flexible backing materials through large area, low cost processes. These gas sensors have been shown to rapidly detect and continuously respond to extremely small changes in the concentrations of gases, including ammonia, carbon dioxide and nitrogen oxide. What's more, they also operate at room temperature and consume very little power. Used in a different setting, the TUM team believes same sort of gas sensor could be used to provide a more effective indicator of food freshness than sell-by dates, and even make it less expensive and more practical to monitor indoor air quality. The technology consists of a single cylindrical molecule - a rolled up sheet of carbon atoms linked in a honeycomb pattern. Laid down in thin films, these randomly oriented carbon nanotubes form conductive networks that can serve as electrodes; patterned and layered films can function as sensors or transistors. "In fact," commented TUM director Professor Paolo Lugli, "the electrical resistivity of such films can be modulated by either an applied voltage (to provide a transistor action) or by the adsorption of gas molecules, which in turn is a signature of the gas concentration for sensor applications." As a basis for gas sensors in particular, carbon nanotubes offer numerous advantages compared to other, more established materials. What has been lacking until now is a reliable, reproducible, low cost fabrication method. The TUM researchers believe spray deposition, supplemented if necessary by transfer printing, meets that need. "To us it was important to develop an easily scalable technology platform for manufacturing large area printed and flexible electronics based on organic semiconductors and nanomaterials," Prof Luigi said. "To that end, spray deposition forms the core of our processing technology."