electron microscope

The electron microscope represents an important variant of the classic microscope. With the help of electrons it can image the surface or the interior of an object.

What is an electron microscope?

In earlier times the electron microscope was also called Over microscope. It serves as a scientific tool that allows objects to be visually enlarged by the application of electronic rays, which enables more thorough investigation.

With an electron microscope, much higher resolutions can be achieved than with a light microscope. In the best case scenario, light microscopes can achieve a magnification of two thousand times. If the distance between two points is less than half the light wavelength, the human eye is no longer able to see them separately.

An electron microscope, on the other hand, achieves a magnification of 1: 1,000,000. This can be traced back to the fact that the waves of the electron microscope are considerably shorter than the waves of light. In order to eliminate disruptive air molecules, the electron beam is focused on the object in a vacuum using massive electric fields.

The first electron microscope was created in 1931 by the German electrical engineers Ernst Ruska (1906-1988) and Max Knoll (1897-1969). Initially, however, no electron-transparent objects were used as images, but small grids made of metal. Ernst Ruska also constructed the first electron microscope in 1938, which was used for commercial purposes. In 1986, Ruska received the Nobel Prize in Physics for his super microscope.

Over the years, electron microscopy has continuously been subjected to new designs and technical improvements, so that the electron microscope has become an indispensable part of science today.

Shapes, types & types

The most important basic types of electron microscopes include the scanning electron microscope (SEM) and the transmission electron microscope (TEM). The scanning electron microscope scans a thin electron beam over a massive object. Electrons or other signals that emerge from the object or are scattered back can be detected synchronously. The intensity value of the image point that the electron beam detects is determined by the detected current.

As a rule, the determined data can be displayed on a connected screen. In this way, the user is able to follow the structure of the image in real time. When scanning with the electronic beams, the electron microscope is limited to the surface of the object. For visualization, the instrument directs the images over a fluorescent screen. After taking pictures, the pictures can be enlarged up to 1: 200,000.

When using a transmission electron microscope made by Ernst Ruska, the object to be examined, which must be appropriately thin, is irradiated by the electrons. The appropriate thickness of the object varies between a few nanometers and several micrometers, which depends on the atomic number of the atoms of the object material, the desired resolution and the level of the accelerating voltage. The lower the acceleration voltage and the higher the atomic number, the thinner the object must be. The image of the transmission electron microscope is created by the absorbed electrons.

Further subtypes of the electron microscope are the cyroelectron microscope (KEM), which is used to examine complex protein structures, and the high-voltage electron microscope, which has a very high acceleration range. It is used to represent large objects.

Structure & functionality

The structure of an electron microscope seems to have little in common with a light microscope. But there are parallels. The electron gun is located on the top. In the simplest case, it can be a tungsten wire. This is heated and emits electrons. The electron beam is focused by electromagnets that have an annular shape. The electromagnets are similar to the lenses in the light microscope.

The fine electron beam is now able to independently knock electrons out of the sample. The electrons are then captured again by a detector, from which an image can be generated. If the electron beam does not move, only one point can be imaged. However, if an area is scanned, a change occurs. The electron beam is deflected by electromagnets and guided line by line over the object to be examined. This scanning enables an enlarged and high-resolution image of the object.

If the examiner wants to get closer to the object, he only needs to reduce the area from which the electron beam is scanned. The smaller the scanning area, the larger the object is displayed.

The first electron microscope to be constructed magnified the objects it examined 400 times. Nowadays, the instruments can even magnify an object 500,000 times.

Medical & health benefits

The electron microscope is one of the most important inventions for medicine and scientific fields such as biology. Fantastic examination results can be achieved with the instrument.

Particularly important for medicine was the fact that viruses could now also be examined with an electron microscope. Viruses are many times smaller than bacteria, so that they cannot be shown in detail with a light microscope.

The inside of a cell cannot be precisely explored with the light microscope either. However, with the electron microscope this changed. Today, dangerous diseases such as AIDS (HIV) or rabies can be researched much better with electronic microscopes.

However, the electron microscope also has some disadvantages. For example, the objects being examined can be affected by the electron beam because it heats up or the rapid electrons collide with entire atoms. In addition, the acquisition and maintenance costs of an electron microscope are very high. For this reason, the instruments are mainly used by research institutes or private service providers.