How Electron Microscopes Work
by Peter Emerson
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Electron microscopes are among the most powerful magnifying tools on the planet. They use beams of electrons rather than conventional light to illuminate objects. The two main types of electron microscopes are transmission electron microscopes and scanning electron microscopes.
Ernst Ruska and Max Knoll constructed the first electron microscope in 1931. They needed an instrument that could examine tiny specimens like components of cells, and conventional light microscopes were not nearly powerful enough. They took the basic principles that guided conventional microscopes and used an electron beam instead of a regular light for illumination. Electron microscopes can enlarge objects up to one million times.
Electron microscopes magnify when electron source creates an electron stream. The electron source is often made of an element like tungsten that is heated until it gives off electrons. The electrons are focused into a stream and the stream is pointed at the object on the stage. There are two kinds of electron microscopes: transmission and scanning.
Transmission electron microscopes give a highly detailed two-dimensional view of tiny objects. They function in a way similar to slide projectors. The subject is placed on a slide. The electron beam is shined through the slide and the electrons that pass through the object are recorded on the other side of the slide, giving the viewer an impression of what the object looks like. Magnetic fields and different apertures are used to focus the electron beam. The subject examined must be sliced extremely thin to provide an accurate representation.
Scanning electron microscopes give a three dimensional view of their subject. Scanning electron microscopes are good for viewing the surface topography of the subject. The electron beam does not pass through the subject, but rather passes over it, scanning the entire surface and projecting a black and white picture onto the screen. Samples need to be placed in a vacuum when using these microscopes to prevent the electrons from being scattered by air or water molecules.
Electron microscopes are used in a number of scientific disciplines. Biologists, chemists, and physicists all use electron microscopes, as well as people in the medical profession. Electron microscopes can magnify objects that are as small as an atom.
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