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The Electron Microscope

As scientists have explored tinier parts of our world, they have needed more and more powerful microscopes. Compound light microscopes served this purpose for many years, but as they could only efficiently magnify up to 2000 times, scientists searched for a way to see even smaller objects. Two German physicists in the 1920s figured out a way to get even greater magnification using a process of electron bombardment.

Diagram of how an electron microscope works.

The idea behind an electron microscope is to fire a stream of electrons with a very small wavelength at the object in question. This allows smaller objects to be distinguished than is possible with light. (The wider wavelength of light allows very small objects to be missed.) This stream of electrons is focused using metal apertures and magnetic lenses1. These beams pass through the specimen and through a series of lenses in the same manner as in a bright field, or standard compound microscope. This allows for magnifications of up to 100,000 times.

The transmission electron microscope shown in the diagram at left is a common type. It generally uses an electron gun to fire monochromatic electrons toward the specimen. From the specimen, they are directed through two condenser lenses that help to focus the beam onto the specimen after it passes through the condenser aperture. It is then directed through the objective and selected area apertures, which enhances contrast and allows the viewer to see ordered arrangements of atoms. The beams are then passed through a series of lenses that ultimately project the image on a screen. Other arrangements allow for different methods of viewing, including on a computer screen.

Next Page: How to Mount Specimens on a Glass Slide

1. UNL on the Electron Microscope

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