Contrast in the electron spectroscopic imaging mode of a TEM

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Abstract
When the zero‐loss transmission falls below 10−3 for biological sections of mass‐thickness greater than 70 μg/cm2, the energy window in the electron spectroscopic imaging (ESI) mode of an energy‐filtering electron microscope (EFEM) can be shifted to the most‐probable energy loss of the electron energy‐loss spectrum. This enables mass‐thicknesses up to 150 μg/cm2 or thicknesses of 1·5 μm to be examined. Electron energy‐loss spectra of thick carbon films calculated by a Fourier method agree with experimental spectra. Measurements of the electron energy‐loss spectroscopy and ESI image intensities with an additional platinum film confirm a scattering model for the calculation of the image intensity. This model considers the angular broadening at the most‐probable energy loss by introducing an effective illumination aperture of the order of the full‐width at half‐maximum of the angular distribution.