Abstract
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 °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 °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 film presents a needle-shaped structure; the needle size ranges between 1 and 3 μm. ZnO-In thin films can detect ammonia concentrations in the range 1–10 ppm by operating between 200 and 500 °C and are selective towards reducing gases like CO and CH 4; a good response towards a few ppm NO x is also observed in the same temperature range. This sensor seems to be suitable for detecting some ppm of ammonia in air.
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