18.6 Electron Microscope
Electron microscope uses the wave nature of electrons whose de Broglie wavelength is thousand times shorter than the wavelength of visible light. Which enables the electron microscope to see final details not visible to the optical microscope. The electrons from a source are passed through the electromagnetic lens called condenser which focuses as the beam on the specimen. The beam is accelerated on applying the voltages of several megavolts. The higher is the speed of electrons, the shorter is the wavelength and hence, higher is the resolution. An electromagnetic lens (objective lens) form the image of specimen. The image is further magnified by the electromagnetic projector lens to photograph the image on a film, called micrograph. A three dimensional image of remarkable quality can be achieved by modern versions called scanning electron microscopes. As stated above, electron microscope can see much smaller details down to nano-metric i.e., about the atomic levels of various materials. The uses include study of cell structure, viruses and bacteria in microbiology, investigation of metal fractures, materials and crystal structure.
(Fig. 18.8: A schematic diagram of the transmission electron microscope.)