Acceptor-like behavior of reducing gases on the surface of n-type In2O3

Studying gas sensing effects in n-In2O3 films, we have observed the anomalous behavior of reducing gases such as CO and H2. At Toper<250-300 deg. C the decrease of In2O3 film conductivity took place during the interactions with CO and H2. Such effect is specific for n-In2O3 interactions with oxidizing gases. Acceptor-like behavior of conductivity has been observed in humid atmosphere only. The In2O3 films were deposited by spray pyrolysis from InCl3-water solutions. Their thickness was varied between 20 and 400 nm. The maximum of acceptor effect took place for In2O3 films with minimal thickness and minimal grain size. The mechanism of CO and H2 interactions with chemisorbed molecular oxygen has been proposed to explain of the observed effect. According to this model, the low temperature CO and H2 oxidation by molecular oxygen is followed by accumulation of atomic oxygen forms (O) on the surface of In2O3. Water plays a role of catalyst in these reactions. Mechanism of such influence is connected with formation of intermediate complexes on the surface of In2O3