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

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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.