Gas‐Sensing Properties of Nanocrystalline WO ₃ Films Made by Advanced Reactive Gas Deposition

Nanocrystalline WO 3 films were produced by advanced reactive gas deposition onto alumina substrates. The as‐deposited films had a tetragonal crystal structure and a mean grain size of around 6 nm, as found by X‐ray diffraction and electron microscopy. Sintering at a temperature τ s > 770 K yielded monoclinic films. We investigated the gas‐sensing properties of films sintered up to 870 K. After an initial “activation” at τ s = 750 K, the nanocrystalline WO 3 films showed excellent gas‐sensing properties, even at room temperature, on exposure to low concentrations of H 2 S in air. As little as 10 ppm of H 2 S made the conductance increase by a factor of about 10 3 within 10 min. The initial properties could be restored by heating the films to 530 K for 1 min.