CONTRAST IN THE ELECTRON SPECTROSCOPIC IMAGING MODE OF A TEM .2. Z-RATIO, STRUCTURE-SENSITIVE AND PHASE-CONTRAST

The ratio of inelastic‐to‐elastic total cross‐sections has been measured in an energy‐filtering electron microscope for different elements. Formulae for the transmission of elastically and inelastically scattered electrons in part I were used to calculate the optimum conditions for a Z‐ratio contrast in the electron spectroscopic imaging mode. Structure‐sensitive contrast can be observed for all non‐carbon atoms in biological sections when filtering with an energy loss at ΔE ∼ 250 eV below the carbon K edge. Model experiments with evaporated layers of different elements on a carbon film allow measurement of the contrast increase. Filtering with the carbon plasmon loss shows a lower phase contrast than with zero‐loss filtering. This can be explained by calculating contrast transfer functions for inelastically scattered electrons. 1990 Blackwell Science Ltd