Scanning transmission electron microscopy

Since its practical realisation by Crewe, STEM utilising a field emission source has become a versatile technique offering many types of signal which can reveal chemical and structural information at the atomic or near-atomic level. Chemical information can be obtained from the electron energy loss spectrum at a spatial resolution which now permits analysis of individual atomic columns. Furthermore the fine structure in these spectra can in many cases rival the structure in X-ray absorption spectra from synchrotron sources. The highly coherent source permits phase relations to be deduced from convergent beam patterns and promises to allow images in both amplitude and phase to be formed at a level of resolution not subject to the usual diffraction and aberration limit. There are a very wide range of applications within solid state science. Finally, the use of the beam to write tailor-made structures for electron optical components and other purposes introduces a wide range of activity requiring FEG STEM. (orig.)