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TRANSMISSION ELECTRON MICROSCOPY
Pages 12 (3012 words)
Transmission Electron Microscopy has revolutionized the field of microscopy, touching a variety of aspects, both biological and physical. Transmission Electron Microscopes (TEMs) comprise a range of different instruments that make use of the properties of electrons, both as particles and as waves.
1. You will be provided with a bright field image (Fig. 1), a dark field image (Fig. 2) and selected area diffraction pattern (Fig. 7) from the same sample. With the support of ray diagrams explain how the images were obtained. Your explanation must include comments about the location and use of the objective and selected area apertures. A TEM consists of condenser lenses to focus the electron beam on the specimen, an objective lens to form diffraction in the BFP (Back focal plane) and the image in image plane, and other lenses to magnify the image or the diffraction pattern on screen. In order to obtain images in TEM, we either focus on the central spot (direct beam), or on the scattered electrons (diffracted beam). This is done by inserting an aperture (selected area aperture) into the BFP of the objective lens followed by selecting the appropriate beam. Bright field image (Figure 1) The given micrograph depicts a dark MgO crystal on a light and bright background. The topography on the face of the crystal is very clear. Such an image is called a bright field image and has a very high contrast. ...
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