A thin film sensor to detect ammonia at room temperature in humid media

a thin film sensor for soils to detect ammonia in aqueous media, operating at room temperature, is reported. the sensor was built by depositing pure tellurium by thermal evaporation in conventional vacuum (10-6 hg mm) on electronic purity alumina substrates fitted with gold electrodes. the resistance of tellurium films was measured when the sensor was exposed to ammonia in humid air. films were characterized by using the following techniques: scanning electron microscopy (sem) to observe films morphology, x-ray diffraction (xrd) and x-ray photoelectron spectroscopy (xps) to look for possible surface tellurium oxides. in every case, specimens were observed or analyzed in its initial state and after being aged in different atmospheres: humidity, air and (ammonia + humidity). the appearance of surface teo2 in te specimens aged in air, enabled to infer a probable sensing mechanism of nh3 in humid media.