What is the principle of transmission electron microscopy?
Electron microscope and optical microscope imaging principle is basically the same, the difference is that the former with an electron beam as a light source, with an electromagnetic field as a lens. In addition, due to the electron beam penetration is very weak, so the specimen used for electron microscopy must be made of ultrathin sections with a thickness of about 50nm. Such slices need to be made with an ultramicrotome. Electron microscope magnification up to nearly a million times, by the illumination system, imaging system, vacuum system, recording system, power supply system consists of five parts, if subdivided: the main part of the electron lens and imaging recording system, placed in a vacuum by the electron gun, condensing mirror, object chamber, objective, diffracting mirror, intermediate mirror, projection mirror, fluorescent screen and camera. An electron microscope is a microscope that uses electrons to visualise the interior or surface of an object. The wavelength of high-speed electrons is shorter than that of visible light (wave-particle duality), and the resolution of a microscope is limited by the wavelength it uses, so the theoretical resolution of an electron microscope (about 0.1 nanometres) is much higher than that of an optical microscope (about 200 nanometres). Transmission electron microscope (Transmission electron microscope, abbreviated TEM), referred to as transmission electron microscope, is an accelerated and aggregated beam of electrons projected onto a very thin sample, where the electrons collide with the atoms in the sample and change direction, resulting in steric angle scattering. The size of the scattering angle is related to the density and thickness of the sample, so that different light and dark images can be formed, and the image will be displayed on the imaging device (such as fluorescent screen, film, and photocoupling components) after magnification and focusing. Due to the very short De Broglie wavelength of electrons, the resolution of transmission electron microscope is much higher than that of optical microscope, which can reach 0.1~0.2nm, and the magnification is tens of thousands~millions of times. Therefore, the use of transmission electron microscopy can be used to observe the fine structure of a sample, or even the structure of just one row of atoms, tens of thousands of times smaller than the smallest structure that can be observed by an optical microscope.TEM is an important analytical method in many fields of science related to physics and biology, such as cancer research, virology, materials science, as well as nanotechnology, semiconductor research and so on.
