Electron microscopes have been commercially available for almost 50 years, and there are now several tens of thousands worldwide, being used in many different fields.

The first electron microscope was a transmission microscope, however it was the scanning microscope that really revolutionized electron microscopy. Currently there is a whole family of electron microscopes that emerged after the numerous investigations carried out in the last twenty years.

These devices combine the possibility of obtaining high-resolution images with chemical analysis of small areas of the material, which is why the field of application of this technique has been greatly increased.

The resolution limit of an optical microscope is determined by the wavelength of light with which the lens is illuminated. The resolution limit can be lowered if you use radiation with a shorter wavelength ( l ).

The effective wavelength of a strongly accelerated electron beam is many orders of magnitude less than that of visible light and even that of ultraviolet light (0.004 nm at 100 kV versus 800-200nm for light). The advantage that electrons on other small particles l is that electrons are easily accelerated by a potential difference and it is possible to being loaded, modify its trajectory in the presence of electric or magnetic fields.

Electron microscopy always works in a vacuum. This is because as it operates with electrons that travel with a predetermined path from the source to their destination, it is essential that this path is not deviated by the presence of atoms or molecules other than those of the sample to be analyzed.

Therefore the column must be as free as possible of gas molecules, this is achieved with powerful vacuum pumps. The pressures at which it works oscillate between 10 -7 and 10 -10 bars, that is, the pressure is reduced below one millionth of the atmospheric pressure.

The interaction of the incident electrons with the sample produces a series of secondary radiations: secondary electrons, backscattered electrons, transmitted electrons, X radiation, Auger electrons, cathodoluminescence and absorbed energy (by the sample). The use of one or the other allows us to obtain different information about the sample.

Types of microscopes

The basis of electron microscopy is the use of an accelerated electron beam as a light source and its focus on the surface of the sample using condenser lenses.

There are different types of electron microscopes, but two are the best known and used: the "Transmission electron microscope (TEM)" or transmission electron microscope and the "Scanning electron microscope (SEM)" or scanning electron microscope .

Both differ greatly in the operating principles as well as in the results obtained with their use. There is also a combination of the previous two, STEM with which a thin sample is analyzed by sweeping its surface. To know more, check out: Advantages of electron microscope

Other lesser-known electron microscopes are:

The ion emission microscope (FIM) that allows observing the atomic structure of the surface of some samples (binding energies of absorbed atoms, corrosion of metal surfaces, crystalline imperfections of some metals).

The tunnel effect microscope (STM) with which an atomic-scale topographic image is obtained (reconstruction of numerous surfaces of materials of great technological interest).