In this article we will discuss about the design of transmission electron microscope, explained with the help of a diagram.
In TEM a finely focused beam of electrons from an electron gun is passed through a specially prepared ultra thin section of the specimen. The beam is focused on a small area of the specimen by an electromagnetic condenser lens. The specimen to be observed is placed on a copper mesh grid. Finally, the electrons are focused by an electromagnetic projector lens (instead of an ocular lens as in a light microscope) on a screen or photographic plate.
The final image in a TEM is known as transmission electron micrograph. The salts of some heavy metals, e.g., lead; osmium, tungsten and uranium are often used for staining. These heavy metal stains are used to increase the contrast between ultra structures and the background. The metals can be fixed on to the specimen and is referred to as positive staining while if used to increase the opacity of the surrounding field it is called negative staining (Fig. 3.4 and Fig. 3.5).