Characteristics of SAW Sensor Based on Diethyl 2-Thienylphosphonate for Detection Sulfur-Containing Agents

A 200 MHz delayline surface acoustic wave (SAW) sensor coated with diethyl 2-thienylphosphonate (DTP) was used to detect 2-chloroethyl ethyl sulfide (CEES). The uniformity of the film was proved by the interface analysis, which included polarizing microscope, atomic force microscope (AFM), and scanning electron microscope (SEM). The contact angles and surface tensions of DTP were discussed and were in the range of 14.78°–17.16° and 27.537–28.145 mN/m, respectively. The works of adhesion (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}_{a}$ </tex-math></inline-formula>) and immersion (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}_{i}$ </tex-math></inline-formula>) were calculated as about −54.401 and −26.661 J, which meant the solution could wet the device surface. Based on the insertion loss test results and the film thickness optimization experiment, the optimal film thickness was about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9~\mu $ </tex-math></inline-formula> m. The reliability analysis of the experimental data was carried out by using the T-distribution and Grubbs test method, and all the 20 groups of data tested were proved to be valid. The sensor had a very wide detection range from 0.25 to 440 ppm for CEES vapor, the sensitivity of the sensor was 0.653 mV/ppm, and the selectivity of the prepared sensor was confirmed in the detection of different gases.