Selective Sensors of Nitrogen Dioxide Based on Thin Tungsten Oxide Films under Optical Irradiation

It is shown that NO2 present in air, beginning at a concentration of 1 ppm, can be selectively detected by sensors based on Au/WO3: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 NO2. A high humidity of air under conditions of room-temperature irradiation additionally increases the device sensitivity to NO2 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 WO3 film.