Imaging diffraction

The major STEM analysis modes are the imaging, diffraction, and microanalysis modes described above. Indeed, this instrument may be considered a miniature analytical chemistry laboratory inside an electron microscope. Specimens of unknown crystal structure and composition usually require a combination of two or more analysis modes for complete identification. 

In electron-optical instruments, e.g. the scanning electron microscope (SEM), the electron-probe microanalyzer (EPMA), and the transmission electron microscope there is always a wealth of signals, caused by the interaction between the primary electrons and the target, which can be used for materials characterization via imaging, diffraction, and chemical analysis. The different interaction processes for an electron-transparent crystalline specimen inside a TEM are sketched in Eig. 2.31. 

The most comprehensive textbook on TEM is that by Williams and Carter (1996). It is written for the microscope operator, and, as well as explaining the use of the instrument for imaging, diffraction and spectroscopy, it also gives an account of the principles of specimen production, and the reader is encouraged to turn to that book for a fuller account of the subject. 

Fig. 2. (a) Ray diagram in the electron microscope under imaging (microscopy) conditions. E electron source C condenser lens S sample O objective lens bfp back focal plane of O I intermediate lens P projector lens, (b) Structural imaging, diffraction and compositional functionalities of TEM. 

TEM Crystal structure and cluster shapes and size No -Direct imaging of clusters -Simultaneous imaging -Diffraction, and analysis -UHV required... 

Surface functionalities mainly for oxygen Fringe imaging, diffraction, light and dark field Atomic distances and coordination chemistry Crystallite sizes, carbon-carbon distribution... 

The most commonly used real space method is transmission electron microscopy (TEM), which can be used for imaging, diffraction or spectroscopy, with spatial resolution on the nanometer to sub-nanometer scale. 

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