Transmission electron objective aperture

We typically view grids in a JEOL lOOCX transmission electron microscope operated at 80 kV with a 40-/Am objective aperture. Use of a low illumination when scanning grids helps to minimize film breakage and specimen contamination. Photographs should be taken as soon as a region of potential interest is spotted to minimize its contamination by the electron beam. 

As in the field of condensed matter sciences, polymer research has made extensive use of conventional transmission electron microscopy (CTEM) ever since its invention. Polymer research focuses on materials that mainly consist of carbon and other light elements. These materials are relatively weak electron scatterers and therefore give low mass thickness and phase contrast. Mass thickness contrast may be enhanced using an objective aperture, staining, and/or low... 

After the radiation has passed through the specimen, the scattered radiation is collected by an objective lens. This lens is the most critical, and imperfections in it will affect the image quality directly. An aperture associated with the objective lens, the objective aperture, is often used in transmission electron microscopy. In optical microscopy the size of the objective lens usually acts as the limiting aperture. 

Transmission electron microscopy illumination has two important differences from light microscopy. One is practical in the TEM the lens powers are continuously variable, but the apertures can be varied only in large steps. This is exactly the opposite of the optical case. The other is that the TEM most often needs a nearly parallel beam of illumination, rather than the strongly convergent beam needed to fill the objective in the optical microscope. 

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