應用石墨烯於掃描式電子顯微鏡液體觀察視窗之製程開發

Abstract

液體槽(Liquid cell)技術出現使得以電子顯微鏡觀測液體中的樣品更為簡單，而電子顯微鏡的高解影像，以及能夠進行臨場動態觀察的優點，讓Liquid cell 技術快速地被應用於各種實驗中。目前以氮化矽薄膜作為Liquid cell 封膜的技術已經商業化，然而氮化矽的厚度無可避免的會導致影像的解析度下降。石墨烯(graphene)是已知最薄的二維材料，具備高強度、高導電性、高熱傳系係數、化學活性安定以及利於細胞吸附等特質，若將其應用於密封液體於電子顯微鏡的真空腔體，以電子顯微鏡觀察液體內物質的解析度則得以提升。本研究開發製程方法，結合石墨烯與氮化矽兩種材料，製備新型態的Liquid cell，我們稱作石墨烯視窗液體槽微晶片(Graphene liquid cell (GLC) microchip)，此新型態Liquid cell以石墨烯做為電子觀察視窗，因此保留了石墨烯的優點，同時利用氮化矽薄膜作為支撐基板，未來可以進一步於Liquid cell 結構內製作液體微流道以及電化學分析用電極。然而這樣的晶片工序繁複，其中石墨烯轉印是具有最多考慮因素的步驟，因此本研究的主要重點之一為嘗試開發可靠的石墨烯轉印的製程，以提高製備GLC microchip的良率成為本研究的重點之一。最後，藉由以掃描式電子顯微鏡觀察不同的液態樣品，比較GLC microchip與氮化矽Liquid cell在影像解析度上的差異。

The advent of liquid cell technology facilitates the observation of liquid samples in electron microscopes. Such a method has been applied to different researching fields because of its high spatial resolution and feasibility of in-situ observations. Thin Si3N4 membranes are commonly used in commercial liquid cells, but the thickness of the Si3N4 membrane inevitably degrades the image resolution. On the other hand, graphene is the thinnest 2D material with high mechanical strength and high thermal and electrical conductivities. It is chemically inert and also a great adhesive layer for biological cells. It is expected that the liquid cell with graphene as the membrane material to seal liquid will have an improved image resolution for electron microscopy. In this research, we use graphene and Si3N4 in the newly designed liquid cell, which is named the graphene liquid cell microchip (GLC microchip). In the GLC microchip, graphene is used as the viewing window, and a suspended holey Si3N4 thin film supports the graphene membrane. The advantageous properties of graphene are preserved in such a liquid cell; besides, microfluidic channels and electrodes can be fabricated on the Si3N4 supporting layer for electrochemical observations. Nonetheless, the fabrication process of the GLC microchip is complicated. Amount the fabricating steps, transferring graphene onto the holey Si3N4 thin film is the most crucial process. Developing a reliable graphene transfer process is one of the major focuses in this study. Finally, we show the improved image resolution by comparing the scanning electron microscopy images of several kinds of nanoparticle solutions taken respectively from the GLC microchip and the conventional liquid cells.