An attempt for NH3 detection based on quartz resonator with thin SnO2 film

The sensitivity of quartz resonators with a thin layer of tin oxide (SnO₂) deposited on them is investigated for the registration of ammonia in air. The measurements are carried out at NH ₃ concentrations from 10 ppm to 5000 ppm. A correlation is found between the relative change of the resonator´s frequency (Δf/f) and concentration in the investigated interval. The dependence can be described by equation such as f(x)=ax^α+b. To obtain the relationship between the thickness of the thin tin oxide and sensitivity of quartz resonator, the thickness of SnO₂ is changed from 40 nm to 120 nm. With increase of thin SnO₂ thickness the resonator´s sensitivity considerably increases. The highest values in the alteration of the frequency of the quartz resonators are registered by a layer thickness of 120 nm. The changes in the sensitivity of sorption as a function of ammonia concentration at different SnO₂ thicknesses are calculated. It is shown that at small concentrations, the sensitivity of the thinner layers is higher than of the thicker. At a concentration of 70 ppm, this dependence becomes inverse and shows a tendency to constant values at concentrations over 5000 ppm. The results obtained show that the quartz resonator-thin SnO₂ film system could be used for detection of NH₃ concentrations down to 10 ppm. Such a system could be used for development of an acoustic sensor for monitoring NH ₃ contamination in the environment