Analysis of Complex, Beam-Sensitive Systems by Electron Microscopy

Complex, electron-beam sensitive systems include organic crystals, polymers, hybrid organic-inorganic materials, some inorganic materials such as hydrates, as well as multiphase solid/liquid and solid/gas systems. Arguably they constitute the majority of systems of current interest across a wide range of scientific and engineering disciplines. We review the use of analytical transmission electron microscopy (TEM) for the characterisation of such beam-sensitive materials and complex, multiphase systems in-situ or close to their native state. Such materials are prone to damage by radiolysis which cannot be eliminated or switched off, requiring TEM analysis to be done within a dose budget so as to achieve an optimum dose-limited resolution and reliable, artefact-free results [1]. We highlight the importance of determining the damage sensitivity of a particular system in terms of characteristic changes that occur on irradiation under both an electron fluence and flux. We discuss the choice of electron beam accelerating voltage and detectors for optimizing resolution and outline the different strategies employed for low-dose microscopy in relation to the damage processes in operation. In particular, we discuss the use of scanning TEM (STEM) techniques for maximizing information content from high-resolution imaging and spectroscopy of materials and the use of cryogenic sample preservation methods. As an example, we describe studies of crystallization processes in the calcium sulfate system using a correlated approach: a combination of liquid cell TEM (LCTEM), in-situ Raman spectroscopy and cryogenic TEM (cryo-TEM). Recent studies have suggested that the calcium sulfate polymorph gypsum (CaSO 4