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This paper discusses the development of a new energy filter (gamma-filter) for improving the image resolution and enhancing the contrast of transmission electron microscope (TEM) images. The energy filter consists of two compact sector magnetic fields and is built into the TEM column.
After being transmitted through a specimen, the electrons travel through the filter in gamma-shaped trajectories. Electrons in a specific range of energies are selected and focused to produce an image.
The energy filter was incorporated into a TEM for observation of unstained biological specimens. With a 1-micrometer thick specimen, zero-loss electrons produced a sharper, or less chromatically aberrant, image as compared with conventional TEMs. On the other hand, with a thin specimen less than 0.1-micrometer thick, 250-eV loss electrons produced a sharp image, while zero-loss electrons did not.
Observations show that a TEM equipped with the new energy filter is useful for microscopy of fine structures of biological specimens under natural conditions.