Electrons are used in transmission electron microscopy (TEM) because the wavelength of electrons is shorter than the visible light. In quantum mechanics, electrons may be considered as particles or waves. Finally, electron diffraction patterns of new materials are investigated. The basic diffraction patterns and the fine structure in the patterns including specimen tilting experiments, orientation relationship determination, phase identification, twinning, second phases, crystallographic information, dislocation, preferred orientation and texture, extra spots and streaks are described in detail. Practical comparisons between various methods of analysing diffraction patterns are also described. The known and unknown materials are identified by indexing patterns. The procedure for indexing simple, complicated and imperfect patterns as well as Kikuchi lines and a combination of Kikuchi lines and spots is outlined. Types of diffraction patterns such as ring pattern, spot pattern and Kikuchi pattern, and general and unique indexing diffraction patterns are explained. The scattering process by an individual atom as well as a crystal, the Bragg law, Laue conditions and structure factor are also discussed. At first, a general introduction including a geometrical and quantitative approach to electron diffraction from a crystalline specimen, the reciprocal lattice and electron diffraction in the electron microscope are presented. Electron diffraction patterns are used to obtain quantitative data including phase identification, orientation relationship and crystal defects in materials, etc. Electron microscopes are usually supplied with equipment for obtaining diffraction patterns and micrographs from the same area of a specimen and the best results are attained if the complete use is to be made of these combined facilities.
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