本研究藉由量測乙醇蒸氣對石英晶體微天平(Quartz Crystal
Microbalance, QCM) 頻率響應的變化， 來測試其作為氣體感測器的可行性。石英為一壓電材料，由於材料內部電雙極 (dipole) 的存在，可因外部施與應力而在晶體表面感應電壓，或由外加電壓而導致晶體的物理形變，具有機電轉換之作用。QCM即利用石英材料之電壓特性，使AT-cut 的石英片在特定頻率下進行水平於切面的剪向震盪(shear mode)，其共振頻率游石英片厚度以及電極表面的負載狀態來決定。藉由量測QCM 共振頻率的改變，可了解電極表面附著物質的狀態，此即QCM 氣體感測器的基本原理。本實驗在電極表面塗佈硬酯酸 (stearic acid) 後，在相同氣體濃度下，QCM 的共振頻率變化量將提昇6 倍，增加量測的靈敏度。因此針對化學感測膜的材料開發、製膜技術、以及量測系統的改良，將可提升QCM 量測的反應速度與準確度。This search determines the possibility of using Quartz Crystal Microbalance, (QCM) as a gas sensor by measuring its resonant frequency shift in ethanol vapor. For a piezoelectric material, like quartz, the inner dipoles in the crystal would induce electric potential on the surface by mechanical strains, or cause mechanical deformation by electric fields. Because of the piezoelectric effect, an AT-cut quartz crystal vibrates in thickness-shear mode of a certain frequency. The resonant frequency is determined by the thickness of the quartz plate and the mass loading on its electrodes. By measuring the change of resonant frequency of QCM, the physical characteristic of the substance deposes on the surface of the electrodes can be understood. This is the basic principle of a QCM gas sensor. The frequency shift of QCM deposited with stearic acid is six times larger then bare QCM in the experiment. The response time and sensitivity of QCM will be improved by the research of the sensing material, film-deposition technique, and measurement system.
