Some details about Electron Microscope

Electron Microscope

                An electron microscope permits the observation of structures as small as 1 mm. This high resolving power is due to the fact that, these microscopes use electrons instead of ordinary light rays. The wave length of visible light's ray is 5000 angstroms. Whereas an electron microscope uses electrons having wave length of only about 0.05 angstroms. This is 100,000 smaller than the wavelength of visible light. 

              In an electron microscope the electrons travel within a vacuum. An electron microscope is built with the following basic structures. 

1. Illumination Source : A cathode filament capable of emitting narrow beam of electrons.

2. Condenser lens : It is an electromagnetic structure capable of collecting and focusing electron beams on the object.

3. Stage : It is meant for holding the specimen. 

4. Objective lens : An electromagnetic structure meant for collecting electrons passing through the specimen. This structure may enlarge the image.

5. 'Eye piece' lens : An electromagnetic projector which further magnifies the image of the specimen and projects it on viewing screen

         Magnification of the image can be increased or decreased by varying current in the projector lens.

Transmission Electron Microscope (TEM)

          A transmission electron microscope just enlarges the object several thousand times. It reveals only the two dimensional image of the specimen being examined. A three dimensional idea of a specimen can be constructed only by taking 1000 to 3000 serial sections of the specimen. Hence it is not possible to visualize the structure of a whole cell.

Scanning Electron Microscope (SEM)

          This microscope produces a three dimensional image of a specimen. In this microscope instead of just recording the electrons passing out of the specimen, the secondary electrons released from the specimen are focused back into the emerging electrons. This arrangement provides a scanning effect.