C O 2 detection using carbon nanotube networks and micromachined resonant transducers

A CO2 sensor using single-walled carbon nanotubes (CNT) and a microelectromechanical system (MEMS) resonator is demonstrated. The MEMS transducer comprises a membrane driven into transverse vibrations by means of Lorentz forces. A downshift in the resonant frequency of the device is measured by a laser vibrometer when changes in the stress state of the CNT film∕membrane structure are caused by adsorption of CO2 onto the nanotubes. The sensor has shown excellent sensitivity, linearity, and recovery over a broad range of concentrations (0–15vol%). In comparison to resistive, dielectric, and gravimetric CNT transducers, this sensor displayed remarkable intrinsic selectivity in the presence of interferences.