What is a transmission electron microscope? What is its final image called?
In TEM a finely focussed beam of electrons from an electron gun is passed through a specially prepared ultra thin section of the specimen. The beam is focussed 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 focussed 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