Phase contrast imaging transmission electron microscop

Figure 14.1. Schematic diagram showing the principle of image formation and diffraction in the transmission electron microscope. The incident beam/o illuminates the specimen. Scattered and unscattered electrons are collected by the objective lens and foeused back to form first an electron diffraction pattern and then an image. For a 2D or 3D crystal, the electron-diffraetion pattern would show a lattice of spots, eaeh of whose intensity is a small fraetion of that of the incident beam. In praetiee, an in-focus image has no eontrast, so images are recorded with the objeetive lens slightly defocused to take advantage of the out-of-focus phase-contrast mechanism.

Phase contrast also appears in electron microscopy. The passage of the wavefront through a specimen causes a phase shift which can be converted into image intensity by interference between the retarded wave with another wave. Components which cause phase contrast have been tried in the transmission electron microscope and do work, but they are impractical. 

FIGURE 1.10 Transfer function calculated for optimum contrast (a) Reproduction of the phase shift sin % from Scherzer (1949) in case of optimum contrast, usually improperly called the extended Scherzer plateau (at 870 A defocus position for the high-resolution transmission electron microscopy used), (b) Effect of defocus on cos %. (Adapted from N. Uyeda et al. Molecular image resolution in electron microscopy. J. Appl. Phys. 43, 5181-5189 (1972). With permission.) (c) Scherzer plateau calculated for Philips CM 20 (200 kV, Cj = 1.2 mm). (From O. Scherzer. The theoretical resolution limit of the electron microscope. J. Appl. Phys. 20, 20-29 (1949). With permission.)... 

Microscopy. Particle size, shape and structure of emulsion droplets can be visualized by various microscope techniques, such as phase contrast light microscopy, confocal scanning light microscopy (CSLM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray microtomography (XRT), atomic force microscopy (AFM) and imaging techniques. 

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