In situ DRIFT studies of surface adsorbates to reveal the detection mechanism of MISiCFET gas sensors

Research Project, 2003 – 2005

The application focuses on the understanding of the detection mechanism of chemical sensors for measuring gas compounds, with special emphasis on MISiCFET sensors for NH3. Metal insulator silicon carbide field effect transistors (MISiCFET) are presently tested in applications like NH3 sensors for control of selective catalytic reduction of NOx in diesel exhausts and sensors for control of the combustion process of boilers. A detailed knowledge of the detection mechanism of chemical sensors is required to achieve high sensitivity, selectivity, speed of response, and long-term stability required by the industry. Today only the detection mechanism for hydrogen is known in some detail. Investigations of the actual gas species adsorbed on the sensor surface, while a gas response is produced have failed to be performed. Only indirect evidences of the species that give rise to the gas response have so far been obtained. The overall goal of this application is to obtain knowledge on the molecular level of the detection mechanism of field effect chemical gas sensors, i.e. correlate the sensor response with the time evolution of surface adsorbates on the sensor. By using infrared spectroscopy we will identify the active sites on the sensor surface, and the adsorbed molecular species involved during the detection of H2, NH3 and CO, respectively, in air between 150-300°C. The project will also result in knowledge, which most probably will be useful in the area of environmental catalysis.