Kotelnikov Institute of Radio Engineering and Electronics of RAS, 125009 Moscow, Russia.
University Laboratory "Nanoscience and Nanotechnology", University of Architecture, Civil Engineering and Geodesy, 1164 Sofia, Bulgaria.
Sensors (Basel). 2022 Dec 22;23(1):100. doi: 10.3390/s23010100.
Properties of the Langmuir-Blodgett (LB) films of arachidic and stearic acids, versus the amount of the films' monolayers were studied and applied for chloroform vapor detection with acoustoelectric high-frequency SAW sensors, based on an AT quartz two-port Rayleigh type SAW resonator (414 MHz) and ST-X quartz SAW delay line (157.5 MHz). Using both devices, it was confirmed that the film with 17 monolayers of stearic acid deposited on the surface of the SAW delay line at a surface pressure of 30 mN/m in the solid phase has the best sensitivity towards chloroform vapors, compared with the same films with other numbers of monolayers. For the SAW resonator sensing using slightly longer arachidic acid molecules, the optimum performance was reached with 17 LB film layers due to a sharper decrease in the Q-factor with mass loading. To understand the background of the result, Atomic Force Microscopy (AFM) in intermittent contact mode was used to study the morphology of the films, depending on the number of monolayers. The presence of the advanced morphology of the film surface with a maximal average roughness (9.3 nm) and surface area (29.7 µm) was found only for 17-monolayer film. The effects of the chloroform vapors on the amplitude and the phase of the acoustic signal for both SAW devices at 20 °C were measured and compared with those for toluene and ethanol vapors; the largest responses were detected for chloroform vapor. For the film with an optimal number of monolayers, the largest amplitude response was measured for the resonator-based device. Conversely, the largest change in the acoustic phase produced by chloroform adsorption was measured for delay-line configuration. Finally, it was established that the gas responses for both devices coated with the LB films are completely restored 60 s after chamber cleaning with dry air.
研究了花生酸和硬脂酸的 Langmuir-Blodgett（LB）膜的性质，以及膜的单层数量与氯仿蒸气检测之间的关系，该研究采用声电高频 SAW 传感器，基于 AT 石英双端口瑞利型 SAW 谐振器（414 MHz）和 ST-X 石英 SAW 延迟线（157.5 MHz）。使用这两种器件，均证实了在固态下，表面压力为 30 mN/m 时，在 SAW 延迟线上沉积有 17 层硬脂酸单层的膜对氯仿蒸气具有最佳的灵敏度，而具有其他层数的相同膜则没有。对于使用稍长的花生酸分子的 SAW 谐振器传感，由于质量负载引起的 Q 因子急剧下降，最佳性能出现在 17 LB 膜层。为了理解结果的背景，使用间歇接触模式的原子力显微镜（AFM）研究了膜的形态，这取决于膜的层数。仅在 17 层膜中发现了具有最大平均粗糙度（9.3 nm）和表面积（29.7 µm）的先进膜表面形态。在 20°C 下，测量了两种 SAW 器件的声信号幅度和相位对氯仿蒸气的影响，并将其与甲苯和乙醇蒸气的影响进行了比较；发现氯仿蒸气的响应最大。对于具有最佳层数的膜，基于谐振器的器件测量到的幅度响应最大。相反，对于延迟线配置，测量到的氯仿吸附产生的声相位变化最大。最后，确定用 LB 膜涂覆的两种器件的气体响应在使用干燥空气对腔室进行 60 s 清洁后完全恢复。
