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Schematic cross-section through a scanning
electron microscope
Seeing Better with Electrons
Just like light, electrons can be bundled and shot at an object. Researchers have
already used this characteristic of electrons in several inventions, such as electron
microscopes that can magnify objects up to 2 million times. One of these micro-
scopes is the scanning electron microscope, or SEM for short. All of the impressive
images shown here were made using one.
To do this, the object of study is bombarded with an extremely thin beam of
electrons. The beam moves over the object in a scanning motion, line by line. De-
pending on the height of the object at any one point, more or fewer electrons are
released from the object by the electron beam hitting it. These electrons are then
registered by a detector and translated into an image by a computer. Black-and-
white images are produced using this method, which are then colored artificially
on the computer.
Despite all advantages and possibilities that an SEM offers, even this device has
its limits. As lively as the pictures of ants or other animals may look, they were
already dead at the time at which the images were made. In order to be observed
in the SEM, the objects have to be coated with an extremely thin layer of gold and
are in a vacuum while they are being observed. With an SEM, you can only dream
of simply going out into nature and studying a pond sample with living organisms
in it like you can do with your light microscope.
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