The influence of mass transport processes on the response to gas mixtures of field-effect devices with large-area catalytic metal gates

A model of how response maps of gas mixtures obtained from large-area field-effect devices with thin catalytic metal gates are affected by the mass transport processes in the gas above the gate has been derived. The model is based on a numerical calculation of the local analyte concentration in the vicinity of the gate of the device. It is found that the catalytic activity of the gate metal may give rise to substantial lateral variations in the analyte concentration at the gate. The varying analyte concentration offers an explanation to the shape of the response maps obtained in earlier experiments. The model is utilized to predict how the analyte mass fraction at the gate, and thus the response maps, should be affected by the gas velocity, the catalytic surface area, and the local consumption rate of analyte at the gate. It is also shown that the geometry of the measurement cell that surrounds the sensing device during measurements may affect the response pictures. The use of the model in connection with distributed chemical sensing and determination of reaction rates is briefly discussed. (C) 1999 American Institute of Physics. [S0021-8979(99)06413-0].