Abstract
The selectivity of a SAW (surface acoustic wave) sensor, with a Co3O4 sensitive thin film for NH3 (ammonia) and the influence of SnO2 on its sensitivity, was studied. Thin films were deposited by pulsed laser deposition (PLD) on quartz SAW sensor substrates. Two sensors with different types of sensitive films were developed: a Co3O4 thin film sensor (S1) and a SnO2/Co3O4 thin film sensor (S2). The sensitive films were deposited in conditions which ensured a porous structure. The sensors were tested in the presence of three gases: NH3, methanol, and toluene. The selectivity of Co3O4 for NH3 was determined from the difference in the frequency shifts of the sensor for NH3 and for VOCs (volatile organic compounds). The positive influence of SnO2 on the sensitivity of sensor S2 was observed from the lower limit of detection (LOD) of this sensor and from the differences in frequency shifts between sensor S1 and sensor S2.
Highlights
Ammonia (NH3) is a substance of interest in various domains
We present the sensing properties of SAW sensors based on SnO2/Co3O4 bilayers, as well as for a single Co3O4 layer, obtained by pulsed laser deposition (PLD)
Porous thin films were deposited by PLD onto the quartz substrates of SAW sensors
Summary
Ammonia (NH3) is a substance of interest in various domains (agriculture, cleaning products, refrigerants, etc.). It is being actively studied for a chemical energy storage, which is crucial for compensating the intermittent character of renewable energy [1]. The use of NH3 requires strict safety precautions, due to the fact that it can lead to severe health problems, and is flammable in air at 50°C at concentrations over 160 000 ppm [2]. Since the maximum permissible exposure limit is 25 ppm, it is important to develop sensors capable of detecting the presence of NH3 at such levels. They are released into the atmosphere by combustion of fuels such as gas, wood, coal, or natural gas but can derive from paints, cigarettes, and other consumer products [4]
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