Electron microscopy of frozen water and aqueous solutions

Abstract

SUMMARYThin layers of pure water or aqueous solutions are frozen in the vitreous state or with the water phase in the form of hexagonal or cubic crystals, either by using a spray‐freezing method or by spreading the liquid on alkylamine treated films. The specimens are observed in a conventional and in a scanning transmission electron microscope at temperatures down to 25 K. In general, the formation of crystals and segregation of solutes during freezing, devitrification and evaporation upon warming, take place as foreseen by previous X‐ray, thermal, optical and electron microscopical studies. Electron beam damage appears in three forms. The devitrification of vitreous ice. The slow loss of material for the specimen at a rate of about one molecule of pure water for every sixty electrons. The bubbling in solutions of organic material for doses in the range of thousands of e nm−2. We propose a possible model for the mechanism of beam damage in aqueous solutions.The structural and thermal properties of pure frozen water important for electron microscopy are summarized in an appendix.