Electron Energy Loss Spectrometry in the Electron Microscope

The main point of spectrometry performed point-by-point using an electron probe of nanometre dimensions is to acquire chemical and electronic information about the defects and interfaces which control structural, electronic and optical properties of materials. According to some, our civilisation now depends upon electrical current sheets travelling along the interfaces between silicon and its oxide; others claim that it depends upon load transfer across the interfaces between weak, ductile metals bonded to strong but brittle fibres. Every polycrystalline material depends upon its grain boundaries, whether for strength or for optical transparency. Analytical electron microscopy, particularly EELS acquired using STEM, is the unique experimental method available to probe the interfacial density of states as well as the chemistry and the structure of such interfaces. Although it is a relatively new technique still improving, it has already solved a number of problems which could not otherwise be tackled. However, its main fundamental limitation is the damage caused to the material by the intense focused probe of electrons in the time required to extract the desired information.