What principle is used in an electron microscope to magnify an object?
An electron microscope is an instrument that uses an electron beam and an electron lens instead of a light beam and an optical lens according to the principle of electron optics to image the fine structure of a substance at a very high magnification.
The resolving power of an electron microscope is expressed by the minimum distance between two neighbouring points that it can resolve.In the 1970s, the resolution of a transmission electron microscope was about 0.3 nanometres (the resolving power of the human eye is about 0.1 millimetres). Nowadays, the maximum magnification of an electron microscope is more than 3 million times, while the maximum magnification of an optical microscope is about 2,000 times, so that the atoms and crystals of certain heavy metals can be directly observed through an electron microscope with a neatly arranged array of atomic dots.
Although the resolution of the electron microscope has been far better than the optical microscope, but the electron microscope needs to work in vacuum conditions, so it is difficult to observe the living organisms, and the irradiation of the electron beam will make the biological samples by irradiation damage. Other problems, such as the brightness of the electron gun and the improvement of the quality of the electron lens also need to continue to study.
The electron microscope consists of three parts: the mirror barrel, the vacuum system and the power supply cabinet. The barrel mainly has an electron gun, electron lens, sample holder, fluorescent screen and camera mechanism and other components, these components are usually assembled from top to bottom into a column; vacuum system consists of a mechanical vacuum pump, diffusion pumps and vacuum valves, etc., and through the pumping pipeline connected to the barrel of the mirror; power supply cabinet consists of a high-voltage generator, the excitation current stabiliser and a variety of regulatory control units.
Electron lens is the most important part of the electron microscope barrel, it is symmetrical to the axis of the barrel of the space electric field or magnetic field so that the electron track to the axis of the formation of the focusing of the role of the glass convex lens to make the role of the beam of light focusing is similar to the role of the glass, so it is called an electron lens. Most modern electron microscopes use electromagnetic lenses, which focus the electrons by a strong magnetic field generated by a very stable DC excitation current through a coil with a pole shoe.
