Carbon nanotubes/ceria composite layers deposited on surface acoustic wave devices for gas detection at room temperature

Surface acoustic wave (SAW) sensor on ATquartz piezoelectric substrate has been designed and fabricated. Test devices were based on asynchronous single-port resonators operating near the 434-MHz-centered industrial, scientific, and medical band. Multi-Walled Carbon Nanotubes/Ceria (MWNTs/CeO2) nanocomposites were used as sensitive layers. The MWNTs were synthesized by catalytic chemical vapor deposition method and coated with nanosized ceria oxide. The composites were deposited on SAW quartz resonator using air-brush technique. MWNTs/CeO2 nanocomposites were characterized using X-ray diffraction, transmission electron and atomic force microscopy. The sensor responses were tested under acetone (C3H5OH) and ethanol (C2H5OH) gases. The output signal was done by S11 parameter of the SAW device and was monitored using a network analyzer. Frequency changes were observed under acetone and ethanol vapors. These changes depended on the surface conductivity of the nanocomposites deposited on the sensor. The single-port SAW gas sensor coated with the MWNTs/CeO2 presented the highest sensitivity in the case of acetone vapor interacting with these layers, with a frequency shift of 200 kHz at room temperature.