Abstract
In this study, zinc oxide (ZnO) was a very good candidate for improving the sensitivity of gas sensor technology. The preparation of an electrospun ZnO nanostructured thin film on a 433 MHz Rayleigh wave based Surface Acoustic Wave (SAW) sensor and the investigation of the acoustoelectric effect on the responses of the SAW sensor are reported. We prepared an electrospun ZnO nanostructured thin film on the SAW devices by using an electrospray technique. To investigate the dependency of the sensor response on the structure and the number of the ZnO nanoparticles, SAW sensors were prepared with different coating loads. The coating frequency shifts were adjusted to fall between 100 kHz and 2.4 MHz. The sensor measurements were performed against VOCs such as acetone, trichloroethylene, chloroform, ethanol, n-propanol and methanol vapor. The sensor responses of n-propanol have opposite characteristics to the other VOCs, and we attributed these characteristics to the elastic effect/acoustoelectric effect.
Highlights
To date, many research groups have studied metal oxidethin film coated Surface Acoustic Wave (SAW) gas sensors to detect CO, H2S, HCHO, NH3, H2, ethanol, methanol and RH [1,2,3,4].Recently, metal oxide nanostructures have attracted attention for chemical sensors as they have unique surface, small-size, and quantum effects.Metal oxide nanostructures typically have a faster response and a lower limit of gas detection due to their very high surface-to-volume ratios
The sensor responses are frequency shifts due to a mass loading. This mass loading depends on the volume of the sensitive material V and the concentration of the solution of the sensitive material
The SEM image was taken from the region between the two IDTs (Figure 2(b)) and shows that the zinc oxide (ZnO) nanoparticles were approximately 50 nm in diameter
Summary
Many research groups have studied metal oxide (such as ZnO, SnO2, TiO2, In2O3, WO3). The gas sensing mechanism of a SAW sensor can be explained as follows: when the sensitive layer absorbs ambient gas molecules, the boundary conditions for the propagating surface are changed, and both the velocity and attenuation of the wave change These changes can be detected with great accuracy by a SAW oscillator as a frequency shift. The interdependence between the electrical potential associated with the SAW and the carriers of the electric charge in the gas-sensitive film leads to a decrease in the velocity This effect depends on the electromechanical effect K2 and the surface conductivity of the layer σs but is independent of the frequency of the wave propagation fo. The acoustoelectric effect on the responses of SAW sensors that are coated with electrospun ZnO nanostructured films was investigated with acetone, trichloroethylene, chloroform, ethanol, propanol and methanol
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