奈米金氣體感測材料之線性溶合能量關係模型與類場效電晶體測試之研究

Abstract

本研究將奈米金氣體感測材料結合微小化化學感測器(阻抗式化學感測器chemiresistor，CR，以及質量式感測器─石英微量天平quartz crystal microbalance，QCM)所組成的氣體感測系統，量測其阻抗及頻率的變化。所使用的氣體感測材料為四種不同的「單層有機分子膜包覆的奈米金簇 (monolayer protected gold nano-cluster，MPC)」，藉由包覆於奈米金表面分子之官能基不同，探討四種具有不同官能基的氣體感測材料對於十六種有機氣體的吸附靈敏度以及反應機構。實驗結果發現，含長碳鏈的奈米金材料對於氣體的吸附較佳，且對於極性氣體之感測靈敏度，有苯環的感測材料優於含酯基的感測材料。接著，我們利用QCM裝置感測有機氣體的量測結果，將其所求得的氣體吸附平衡常數K (partition coefficient) 與待測氣體之溶劑參數進行多元線性迴歸，分別計算出四種材料的線性溶合能量關係模型 (linear solvation energy relationship model，LSER model)，並藉由此模型探討各材料中，氣體吸附平衡常數與各化學作用力之間相關連的程度，實驗結果發現作用力中的極性與氫鍵酸之作用，對於Au-ESTER在吸附氣體時的影響較大，凡德瓦力則是和碳數多的Au-C8與Au-10C較相關；此外，我們將氣體的溶劑參數分別代入四種氣體感測材料的LSER model之中，得到的 值與實驗結果有相同的趨勢，因此此模型可以用來作初步簡易的吸附選擇性預測；最後，嘗試將微小指叉電極改製成類似場效電晶體的構造，塗佈上兩種氣體感測材料Au-TBT和Au-C8，進行電性量測，結果在電壓增加到某個大小後，電流值會陡升，並觀察當輸入閘極電壓進行氣體感測時靈敏度之變化，結果靈敏度是沒有提升的現象。In this study, we measured the resistance and frequency changes of CR (chemiresistor) and QCM (quartz crystal microbalance). We synthesized a series of monolayer protected gold nano-cluster (MPC) as the sensing materials that were modified by various moleculars with functional groups, and investigated the sensitivity and the mechanisms of vapor sensing on CR and QCM by detecting 16 volatile organic compounds (VOCs). We found that MPC with long carbon chains have good absorbability to vapors, and those MPC with benzene ring have the better absorbability to polar vapors than those with ester group. The second part of study using multiple linear regression is to obtain linear solvation energy relationship model (LSER model) of four vapor sensing materials by investigating the relationship among the solvent parameters toward the partition coefficient K. The coefficients of LSER models are regarded as the interaction between the vapor sensing materials and the vapors. We discussed the corr- elations between five solvent parameters and partition coefficient K by LSER models. As a result, polarity and acidic hydrogen bonding have significant influence on Au-ESTER. On the other hand, materials such as Au-C8 and Au-10C with long carbon chains are associated with van der Waals’ force. In addition, the value from LSER models and the experimental results showed the similar trend, therefore, the models can be used to predict the selectivity for adsorption of vapors onto materials at. Finally, we measured the conductivity and sensitiv- ity of quasi-FET (field effect transistor) coated with Au-TBT and Au-C8 when applied specific gate voltages on them. The sensitivities showed no improvement but increasing in current when the applied voltage is large enough.