Electron scattering experiments using a post-column imaging electron energy filter

An imaging electron energy filter in combination with a conventional electron microscope is used to record the intensity distribution of elastically scattered electrons. To automate the intensity acquisition to a high degree and to allow pixel-precise operations, the whole system is operated under remote control by external computers using a script-based program. The intensity is recorded on a slow-scan CCD camera with high linearity, and integration of pixel intensities results in a high S/N ratio. Subsequent acquisition of parts of the diffraction pattern yields a high dynamic range (19 bits), and large scattering lengths of 300 nm(-1) can be achieved. The intensities are used to calculate the pair distribution function (PDF) with an accuracy of 0.03 nm in real space. Atomic pair distances up to I nm can be determined. The method is tested at polycrystalline gold and nickel films, and it is applied to vitreous silica and amorphous carbon. The results are in very good agreement, for example to the PDF obtained from neutron scattering at vitreous silica. (C) 1998 Elsevier Science B.V. All rights reserved.