■ Quantitative gas detection with semiconductor micro-sensors and chemometrics

The sensitive element that we developed is a sintered tin dioxide bar (2.5 〈 0.5 〈 0.5 mm) [3]. It is stuck on an alumina substrate (Fig. 1) with an integrated heating system (20 to 500 °C). The variations of electric conductivity are due partly to a modification of the point defects of the semiconductor in the presence of oxidizing or reducing gases. But they are also related to the catalytic reactions of surface, in particular in the presence of organic gases or vapours [2,5]. The curves conductance-temperature G = f(T) of some sensors may be characteristic of the gases present in air (Fig. 2). It is then necessary that these data be acquired in decreasing temperature in order to avoid memory effects.