Selective sensors of nitrogen dioxide based on thin tungsten oxide films under optical irradiation

It is shown that NO$_{2}$ present in air, beginning at a concentration of 1 ppm, can be selectively detected by sensors based on Au/WO$_{3}$ : Au thin films activated by laser diode radiation with maximum intensity at 400 nm instead of constant heating. The radiation-activated photodesorption reduces the time of sensor response to NO$_{2}$. A high humidity of air under conditions of room-temperature irradiation additionally increases the device sensitivity to NO$_{2}$ due to the appearance of additional adsorption sites. The absence of a sensor response to reducing gases and varying oxygen concentration in the atmosphere is caused by the photodesorption of chemisorbed O$_{2}^{-}$ species during their interaction with holes generated in intrinsic optical transitions in the near-surface region of WO$_{3}$ film.