An energy filter for high voltage electron microscopy

An energy filtering device has been designed for the 1.2MV high voltage electron microscope. It is made up of three magnetic prisms. Because the system has a plane of symmetry it has special properties with respect to stigmatism and achromatism. It can be operated at up to 1.2MV as either a transmitted electron energy analyzer or an image energy filter. In the first mode, a 3eV energy resolution has been measured at 1MeV allowing the study of various types of inelastic scattering with energy losses up to a few thousand eV. When the system is used as a filter, images have been obtained by selecting electrons having energy losses of up to a few hundred eV. The general quality of the image is preserved. The spatial resolution remains that of the unfiltered image. The filtered image is free of aberrations for an imaged area a few microns in diameter