The response of quartz crystals coated with thin fatty acid film to organic gases

We tried to apply a quartz crystal as a sensor by using the resonant freque ncy and the resistance properties of quartz crystals. Foul kinds of fatty a cids that have the same head groups were coated on the surfaces of the quar tz crystals, and the shift of the resonant frequency and the resistance wer e observed based on the lengths of the tail groups. Myristic acid (C-14), p almitic acid (C-16), stearic acid (Cls), and arachidic acid (C-20) were dep osited on the surfaces of quartz crystals by using the Langmuir-Blodgett (L B) method. As a result, the resonant frequency change was more sensitive to high molecular-weight fatty acids than to low molecular-weight ones. We al so observed the effect of temperature on stearic acid LB films, and the res ponse properties of quartz crystals coated with stearic-acid LB films to or ganic gases were investigated. As a result, the sensitivity of quartz cryst als to organic gases was higher for higher molecular-weight gas, and we fou nd that quartz crystals coated with stearic-acid LB film were more sensitiv e to organic gas than bare quartz crystals at room temperature.