NO2 gas sensing based on vacuum-deposited TTF–TCNQ thin films

The sensing characteristics of tetrathiafulvalen–tetracyanoquinodimethane (TTF–TCNQ) thin films for detecting nitrogen dioxide gas are studied. TTF–TCNQ complex, which is obtained by dissolving TTF and TCNQ powders in a solvent, is thermally evaporated onto a Al2O3 substrate screen-printed with interdigitated gold electrodes. The gas sensing properties for the NO2–TTF–TCNQ interaction, including conductance transient and sensitivity, are discussed. When the special sensing condition of short contact time or lower concentration range is satisfied, a linear relationship is obtained by plotting the rate of conductance change versus NO2 concentration, from which a sensitivity value of 8.0±0.1×10−3 μS/s ppm is obtained. The rate of conductance change measured at room temperature is linear with respect to the NO2 gas concentration up to 30 ppm. Moreover, by comparing with the literature, the conductivity calculated for the vacuum evaporated TTF–TCNQ thin films suggests that the molecular structure of the complex is randomly oriented.