Electron microscope
An electron microscope is a scientific instrument which uses a beam of electrons to examine objects on a very fine scale. In an optical microscope, the wavelength of light limits the maximum magnification that is possible. As electrons have a smaller wavelength, they can achieve a higher magnification, and can see very small objects - typically around 1,000 times smaller than those seen in an optical microscope. The outline of objects, as revealed by the flow of electrons, is changed into a picture using visible light for people to see. Electron microscopes were invented in Germany in the 1930s.
Types of electron microscope
Transmission Electron Microscope (TEM)
A beam of electrons is sent towards the specimen - some electrons are reflected, while some pass through. Those that pass through are detected and used to form an image of the specimen at a magnification of about 500,000 times. This microscope is more powerful than a light microscope.
Reflection Electron Microscope (REM)
Similar to a Transmission Electron Microscope, but the reflected electrons are detected. By measuring the reflected electrons, some information about the surface of the specimen can be gathered.
Scanning Electron Microscope (SEM)
Electron Microscope Media
A transmission electron microscope from 2002
An image of an ant in a scanning electron microscope
Reproduction of an early electron microscope constructed by Ernst Ruska in the 1930s
Operating principle of a transmission electron microscope
A cross-sectional, simplified diagram of a transmission electron microscope.
Operating principle of a scanning electron microscope
Image of Bacillus subtilis taken with a 1960s electron microscope
An insect coated in gold for viewing with a scanning electron microscope (SEM)
Freeze-fracturing helps to peel open membranes to allow visualization of what is inside
External face of bakers yeast membrane showing the small holes where proteins are fractured out, sometimes as small ring patterns.
A narrow beam of electrons is moved across the specimen and a picture is built up piece by piece by detecting how the electrons are reflected or absorbed as it moves.
Scanning Transmission Electron Microscope (STEM)
It combines the high magnification of TEM with the better surface detail of SEM. It can be used to perform complex analysis on the specimen, which cannot be done using TEM alone.