Development of TEM specimen Holder Enabling Atomic Level Observation under One Atomospheric Pressure

环境电池(EC)技术可用于研究不同环境气氛下的水合和催化样品等。在本研究中，我们开发了一种薄膜密封型EC，它可以在一个大气压下进行原子级观测。所研制的电镜柱具有连接电镜柱和镜筒外部的通道，因此，可以通过调节气体流量来控制样品环境的气体压力。通常情况下，EC必须有一些窗口以供电子束通过，并且需要一些覆盖在窗口上的密封膜来保护气体泄漏到显微镜柱中。EC最重要的部件是密封膜。薄膜必须承受大气压以上的压力，并保持薄膜的高电子透过率、无定形性等性能。在本研究中，我们成功地制备了一种厚度为20 nm的碳膜，它可以承受一个大气压或更大的压力。在碳膜和金属支撑栅之间夹有一层厚度约150 nm的三乙酰纤维素(TAG)缓冲层，有效地实现了对气体压差的抵抗。此外，还研制了一种将电子显微镜样品夹持器插入EC的装置，并在一个大气压下成功地观察到了二氧化钛粉末样品。通过向样品中引入反应气体，可以在原子尺度上观察到二氧化钛的催化行为。对达到的分辨率的精确评估现在正在检查作为大气压力和密封膜厚度的函数。高速电子入射产生的等离子体有时会对被观测样品造成损伤，目前正在进行基于蒙特卡罗计算机模拟的研究。

An environmental cell (EC) technique is useful for the study of hydrated and catalytic specimens etc. under various environmental atmosphere by a transmission electron microscope. In the present study, we have developed a film-sealed type EC which enables atomic level observation under one atmospheric pressure. The developed EC has the passages connecting the EC and the outside of the microscope column, therefore, the gas pressure of the specimen environment can be controlled by adjusting the gas flow. In general, the EC must have some windows for electron beam passage and some sealing films covering the windows are necessary to protect the gas leakage into the microscope column. The most important component of the EC is the sealing film. The film must withstand above atmospheric pressure with maintaining properties such as high electron transmittance, amorphousness of the film and so on. In the present study, we succeeded to make a carbon film of 20 nm thick which,withstands the pressure of one atmospheric pressure or more. A buffer layer of triacetylcellulose (TAG) film of about 150 nm in thickness was sandwiched between the carbon film and the metal supporting grid, which works very effectively to realize the resistance to the gas pressure difference. An apparatus to insert the TEM specimen holder with the EC was also developed and TiO2 powder sample was successfully observed at one atmospheric air pressure. By introducing reaction gas to the sample, catalytic behavior of TiO2 might be possible to observe in atomic scale. Precise evaluation on the achieved resolution is now under examining as a function of the atmospheric pressure and the thickness of the sealing film. Plasma induced by high speed electrons incidence sometimes gave damages to the observed sample, which is under investigation based on Monte Cairo computer simulations.