Peter Hesketh Professor, Micro and Nano Engineering Georgia Institute of Technology
Abstract Metal Organic Frameworks (MOFs) are a new class of nanoporous materials which have a high surface area, thermal/chemical stability and a tailorable pore size. HKUST-1 MOF was selected due to large internal surface area, excellent stability and known properties. Mechanical strain is generated upon adsorption of analytes into the MOF; it is proportional to concentration and is a function of adsorbed species. Piezoresistive microcantilever sensors are microfabricated devices that are highly sensitive to surface strain due to doped single crystal silicon regions. A thin film of HKUST-1 was grown at room temperature using layer-by-layer techniques. Changes in resistance generated by surface strain can be measured with a high degree of accuracy using a Wheatstone bridge and simple instrumentation. Dry nitrogen was used as a carrier gas to expose devices to varying concentrations of twelve different VOCs. Results show that stress-induced piezoresistive microcantilever array sensors with MOF coatings can provide a highly sensitive and reversible sensing mechanism for water vapor and methanol. Characteristic response features allow discrimination based on shape, response time constants and magnitude of response for other VOCs. The microcantilever sensors were shown to be durable, reliable and stable in long term testing despite being exposed to many different analytes. This work shows a promising new technology for a next generation sensors for gas monitoring. The key advantages of this type of sensor are the higher sensitivity with a nano-porous MOFs, reversible response, single chip sensing system and low power operation.