Low-Temperature Transmission Electron Microscopy

Abstract

During the past 60 years, the transmission electron microscope (TEM) has been used to investigate the fine structure of practically all the main categories of the inorganic and organic components of our planet and—in some notable instances—a few extraterrestrial objects. All these investigations have made use of the very high spatial resolution available in the microscope, which currently hovers around 2–3 Å. The physical events on which TEM relies are well characterized and need not concern us here except to appreciate that the processes of imaging and recording involve energy transfer to the sample and will also damage the sample, particularly those of an organic constitution. Scherzer (1949) calculated that an electron dose of 10,000 e ⁻ nm⁻² is needed to take a high-resolution image with sufficient contrast; we now know that in some cases, only 100 e ⁻ nm⁻² are needed to damage a specimen. The images of most organic and biological material examined in the TEM have a very low amplitude contrast, which can only be ameliorated by staining with heavy metals. The presence of water in almost all biological material was solved by the draconian expedient of removing it and then replacing it with plastic.