Making Graphene Membranes in Electron Microscopy Liquid Cells

• Main Authors: Yu-Ting Hong, 洪郁婷
• Other Authors: Cheng-Yen Wen
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/vw5p8t

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 106 === The development of liquid cells has marked a milestone of in-situ observation. It is a very useful tool in many research fields, such as observing cells in aqueous solution in the field of biology, and watching the growth and coalescence behavior of nanoparticles in materials science. Recently, the invention of graphene liquid cell provides a better resolution for observing liquid samples in an electron microscope. The outstanding physical properties of graphene, including its high strength, high electron transparency, high chemical stability, and the thickness of one atomic layer, are utilized as the membrane material in the liquid cells. On the other hand, the process to use silicon nitride as the window membrane on liquid cell microchips is already mature. Besides, other functions, e.g. liquid flow, electrical biasing, or heating, can be integrated. However, the thickness of the silicon nitride membrane lowers the image resolution. In this research, we aim to make a graphene liquid cell microchip, which exhibits the merits of liquid cell microchips and the graphene liquid cell. We replace the silicon nitride window membrane with a multilayer graphene film in order to obtain better image resolution, and, meanwhile, the possibility of integrating multiple functions on silicon-based microchip is preserved. The first step in the fabrication process of graphene liquid cell microchip is wafer dicing and cleaning. The second step is to produce the holey pattern of the silicon nitride supporting window membrane by means of photolithography and reactive ion etching of the standard semiconductor processes. Than silicon substrate underneath the silicon nitride membrane is removed by anisotropic etching using potassium hydroxide solution. Finally, CVD graphene sheets are transferred onto the microchip layer by layer to make a multilayer graphene film as the membrane on the microchip. Scanning electron microscope, transmission electron microscope and Raman spectrometer are used to examine the coverage and quality of graphene on the holey supporting window. A holder is designed for the graphene liquid cell microchip for testing the leakage in vacuum and the observations of dispersed gold nanoparticles in aqueous solution in a scanning electron microscope.