The ability to observe directly and at high spatial resolution the interactions between environments and materials affords the material scientist new and unique opportunities. This capability is realized in the Environmental Cell Transmission Electron Microscope Facility which has been installed as part of the Center for Microanalysis of Materials at the Materials Research Laboratory of the University of Illinois at Urbana-Champaign.The Facility is based on a JEOL 4000EX equipped with a specially designed pole piece. An aperture limited, differentially pumped, environmental cell has been installed in this pole piece. The system is shown schematically in Figures 1 and 2. Figure 1 is a plan view of a section through the objective lens pole-piece, with the microscope axis perpendicular to the plane of the paper, showing the cell enclosing the sample rod, the gas handling system and the location of the magnetically levitated Turbo-Molecular pumps. Figure 2 shows a cross-sectional view of the environmental cell and the gas handling system. As shown in Figure 2 the electron beam passes through a series of five apertures which allow the column vacuum to be maintained while the cell pressure is increased. The actual cell apertures are located at the apex of cones to minimize the gas path length, allow maximum tilt and still permit high- angle diffraction data to be obtained. Differential pumping of the cell is achieved by the four turbo- molecular pumps, the location of which can be seen in the Figures. With this arrangement the environmental cell is capable of supporting 400 torr of N2 gas which has no noticeable effect on the microscope operation. This allows the microscope to be operated with a LaB6 filament. The gas handling system was designed to handle a variety of environments including corrosive ones.
