Liquid containing specimens can be stabilized for observation in the Environmental Scanning Electron Microscope (ESEM). It is also possible to examine systems that are primarily liquid, such as colloidal suspensions and gels, or even possess a multi-component liquid microstructure as in emulsions.(l) In order for such investigations to be useful, an understanding of the origins of secondary electron contrast in liquids is necessary. Our aim here is not to produce a complete theory of secondary electron emission in these systems, but to provide general guidelines for discriminating between two liquids based on relative contrast.Secondary electron emission from a substance is determined by three processes: creation, transport through the material, and escape from the surface.(2) Contrast between two regions will be due to differences in one or more of these processes. Initial generation of secondary electrons is primarily a function of the ionization cross-sections of the substance and its density.
