Electron microscopy and structure images

The intensity of a powder diffraction ring is then written as  

In essence, a powder diffractogram contains as much information as a single crystal experiment. When the intensity and the positions of the diffraction pattern are taken into account, the pattern is unique for a single substance. The X-ray diffraction pattern of a substance can be likened to a fingerprint. In effect, the pattern of lines on the powder diffraction pattern of a single phase is virtually unique, and mixtures of different crystals can be analysed if a reference set of patterns is consulted. 

Another correction factor arises because the X-ray beam is absorbed as it passes through the sample. The effect of this is to reduce the intensities of reflections that pass through large volumes of sample compared to those that pass through small volumes. Correction factors will depend upon sample shape and size, and a general formula applicable to all sample geometries can- 

It is apparent that, given a crystal structure, it is quite an easy matter to compute both the positions, the intensities and the phases of the diffracted beams that arise when the crystal is irradiated. The main task that faces the crystal-lographer, however, is to derive an unknown crystal structure from experimentally collected diffraction data. To understand the physical 

4There are a number of different types of electron microscope, but for the present purposes they can be divided into two categories, scanning and transmission. Scanning electron microscopy, broadly speaking, is used to reveal surface topography, while transmission electron microscopy is of more relevance to crystal structure determination. This is the only type of electron microscopy considered here. 

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