Gas response times of nano-scale SnO2 gas sensors as determined by the moving gas outlet technique

We report on measurements of the gas response time of pure and platinum (Pt) catalysed SnO2 films using the moving gas outlet method. In this mode of operation changing gas flows are forced directly onto the sensor surface to avoid the formation of a stagnant layer and to reveal gas response times unaffected by the usual diffusive delays. We find that the intrinsic response and recovery time constants τ follow an exponential temperature dependence τ(T) = τ0exp(Ea/kBT), with Ea standing for the activation energies for adsorption or desorption, respectively. We find that catalytic enhancement lowers the activation energies both for adsorption and desorption, with the more pronounced changes generally taking place in the case of the adsorption time constants. We further show that catalyst-induced changes in Ea are accompanied by changes in the prefactor τ0 which partly compensate the accelerating effect of a lower Ea.