The electron microscope represents a significant variation of the classic microscope. With the help of electrons, it can image the surface or interior of an object.
What is an electron microscope?
The electron microscope represents a significant variation of the classical microscope. In earlier times, the electron microscope was also known as the supermicroscope. It serves as a scientific instrument through which objects can be magnified pictorially by the application of electronic beams, allowing for more thorough examinations. Much higher resolutions can be achieved with an electron microscope than with a light microscope. Light microscopes can achieve a magnification of two thousand times in the best case. However, if the distance between two points is less than half the wavelength of light, the human eye is no longer able to distinguish them separately. An electron microscope, on the other hand, achieves a magnification of 1:1,000,000. This can be attributed to the fact that the waves of the electron microscope are considerably shorter than the waves of light. To eliminate interfering air molecules, the electron beam is focused on the object in a vacuum by massive electric fields. The first electron microscope was developed in 1931 by the German electrical engineers Ernst Ruska (1906-1988) and Max Knoll (1897-1969). Initially, however, small metal gratings rather than electron-transparent objects served as images. Ernst Ruska also constructed the first electron microscope used for commercial purposes in 1938. In 1986, Ruska received the Nobel Prize in Physics for his supermicroscope. Over the years, electron microscopy has been continuously subjected to new designs and technical improvements, so that in the present day it is impossible to imagine science without the electron microscope.
Shapes, types and kinds
The main basic types of electron microscope include the scanning electron microscope (SEM) and the transmission electron microscope (TEM). The scanning electron microscope scans a thin electron beam across a solid object. Electrons or other signals that re-emerge from the object or are backscattered can be detected synchronously. The detected current determines the intensity value of the pixel that the electron beam scans. As a rule, the determined data can be displayed on a connected screen. In this way, the user is able to follow the buildup 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 across a fluorescent screen. After photography, the images can be magnified up to 1:200,000. When using a transmission electron microscope, originated by Ernst Ruska, the object to be examined, which must have an appropriate thinness, is irradiated by the electrons. The appropriate thickness of the object varies from a few nanometers to 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 accelerating voltage and the higher the atomic number, the thinner the object must be. The image of the transmission electron microscope is formed by the absorbed electrons. Other subtypes of the electron microscope include the kyroelectron microscope (KEM), which is used to study complex protein structures, and the high-voltage electron microscope, which has a very high acceleration margin. It is used to image extensive objects.
Structure and mode of operation
The structure of an electron microscope seems to have little in common with a light microscope on the inside. Nevertheless, there are parallels. For example, the electron gun is located on the top. In the simplest case, this can be a tungsten wire. This is heated and emits electrons. The electron beam is focused by electromagnets, which have a ring-like shape. The electromagnets are similar to the lenses in a light microscope. The fine electron beam is now able to independently knock electrons out of the sample. The electrons are then collected 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 the scanning of a surface takes place, a change occurs. The electron beam is deflected by electromagnets and guided line by line over the object to be examined. This scanning enables a magnified and high-resolution image of the object. If the examiner wants to get even 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 that was constructed magnified the examined objects 400 times. In modern times, the instruments can magnify an object even 500,000 times.
Medical and health benefits
For medicine and scientific branches such as biology, the electron microscope is one of the most important inventions. Thus, fantastic examination results can be obtained with the instrument. Particularly important for medicine was the fact that viruses could now also be examined with an electron microscope. Viruses, for example, are many times smaller than bacteria, so they cannot be imaged in detail by a light microscope. Nor can the inside of a cell be fathomed in detail with light microscopes. However, this changed with the electron microscope. Nowadays, dangerous diseases such as AIDS (HIV) or rabies can be investigated much better with electronic microscopes. However, the electron microscope also has some disadvantages. For example, the objects examined can be affected by the electron beam because of heating or because the speeding electrons collide with complete 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.
