Analytical transmission electron microscopy

Abstract

Analytical transmission electron microscopy (TEM) is used to reveal sub-micrometer, internal fine structure (the microstructure or ultrastructure ) and chemistry in minerals. The amount and scale of the information which can be extracted by TEM depends critically on four parameters; the resolving power of the microscope (usually smaller than 0.3 nm); the energy spread of the electron beam (of the order of an electron volt, eV); the thickness of the specimen (almost always significantly less than 1 μm), and the composition and stability of the specimen. An introductory text on all types of electron microscopy is provided by Goodhew et al. (2001), while more detailed information on transmission electron microscopy may be found in the comprehensive text of Williams and Carter (2009). ### Basic design of transmission electron microscopes (TEM) The two available modes of TEM—CTEM and STEM—differ principally in the way they address the specimen. Conventional TEM (CTEM) is a wide-beam technique, in which a close-to-parallel electron beam floods the whole area of interest and the image (or diffraction pattern), formed by an imaging (objective) lens after the thin specimen from perhaps 106–107 pixels on a digital camera, is collected in parallel . Scanning TEM (STEM) deploys a fine focused beam, formed by a probe-forming lens before the thin specimen, to address each pixel (here, a dwell point) in series and form a sequential image as the probe is scanned across the specimen. Figures 1 and 2 summarize these different instrument designs; here it should be noted that many modern TEM instruments are capable of operating in both modes, rather than being instruments dedicated to one mode of operation. In both types of instrument analytical information from a small region is usually collected using a focused beam. The smallest region from which an analysis can be collected is defined by the diameter of …