An electron microscope is a device for watching with a very high resolving power, which allows you to take a close look at samples of sizes extraordinarily small, almost infinitesimal, thanks to the wave properties of one or more electron beams.
The main features of an electron microscope
In parallel with the geometrical optics we have seen the development of a new branch of optics that p was called optical electronics and taking Foundation by the thought of physical scientist called De Broglie. It was 1024 when the scholar was based on the concept of photon, which assigned in light of material properties, to formulate the hypothesis that the material particles could behave like light beams, and can then be equipped with wavelike properties.
Based on this thinking it was possible to create an electron microscope that works by sending the sample to be analyzed an electron beam and analyzing the figures of diffraction which arose. The main advantage of this type of instrument obviously lies in a very high resolving power, which becomes as big as big is the wavelength de beam of light used. Visible light has a wavelength whose value is around an average of around 5000 in, while an electron beam accelerated to about 100 kV has a wavelength of approximately 0.05 to: This means a greater resolving power of about 100,000 times!
This powerful tool allows us, therefore, to observe the minimum facilities and the smallest details that it would be impossible to capture using a normal light microscope, however powerful it may be. The amazing results of an electron microscope are amazing especially as regards studies in biology, metallurgy and medicine.
As regards the technical characteristics, this instrument consists of an electron source, a lens that acts as a magnetic capacitor and that serves to focus the electron beam on the sample you want to observe, from a magnetic lens that acts as a lens, from another magnetic lens always acting as projector and blocking electrons in optical system field , and finally from an item you need to collect the images returned from the microscope, which can then be a photographic plate, a film or a fluorescent screen. The entire system is maintained under vacuum to prevent unwanted electron beam disturbances may occur.
How does the electric microscope
The source of electrons in an electron microscope is represented by a very thin tungsten filament V-shaped, whose negative potential difference is maintained between 30 and 100 kV. The electrons then pass into magnetic capacitor through a hole that is in the anode; the capacitor is intended to adjust the intensity of the electron beam convergence.
The electron beam must be hitting the sample to be observed, which then undergoes the diffraction. Sample parts that cause greater deviation of radiation are thicker and denser ones, which are then darker in the resulting image. To adjust the sharpness of the image you make a current regulation, more precisely in the winding magnetic lens. By replicating this action on the projector you can adjust the magnification of the image.
Scanning electron microscope (SEM)
In this variation of electron microscope, electron beam strikes the sample causes the emission from the same sample of many particles, among which there are also secondary electrons. They are to be identified by a special detector, before being converted into electrical impulses. In this tool the electron beam is not fixed but scanned: ç passes, that is, the sample line by line, into a sequence of rectangular areas.
The transmission electron microscope (TEM)
In this type of electron microscope on the electron beam, before hitting the sample, pass in an area where it has been artificially created a vacuum, and only after passing through the test material.
The ion microscope
The ion microscope is a variation of the electron microscope, built in 1936 by a scholar named Muller. The microscope is the most powerful of all ion microscopes and provides resolutions of the atomic level, with a magnification of about 1.000.000 of diameters.
The ion microscope consists of a cathode with a needle-like tip, on which is sited the specimen to be observed, contained in a small spiral. Then there is a heating which allows a vacuum evaporation; This process creates a very strong electric field between the cathode and the anode, which is intended to accelerate positive ions that originate from the sample to be examined. These ions then strike a fluorescent screen that allows you to view an enlarged image of the area being examined.
This complex instrument is used primarily to examine the surfaces of compound patterns conductors, metals and alloys, as well as for examining phenomena such as catalysis.