A NOVEL METHOD FOR THE PREPARATION OF NH3 SENSORS BASED ON ZNO-IN THIN-FILMS

This paper reports the preparation of ZnO-In thin films that are capable of detecting low ammonia concentrations in air. Indium and zinc layers are subsequently deposited by thermal evaporation at 70 degrees C onto an alumina substrate; the metal-semiconductor phase transformation is obtained on thermal cycling of the films in a synthetic air flow at a maximum temperature of 500 degrees C. XRD analysis shows that these films are polycrystalline and are slightly oriented in the (002) direction. SEM micrographs show that the surface of the metal-oxide him presents a needle-shaped structure; the needle size ranges between I and 3 mu m ZnO-In thin films can detect ammonia concentrations in the range 1-10 ppm by operating between 200 and 500 degrees C and are selective towards reducing gases like CO and CH4; a good response towards a few ppm NOx is also observed in the same temperature range. This sensor seems to be suitable for detecting some ppm of ammonia in air.