Principles of Electron Microscope Composition
The electron microscope consists of three parts: the mirror barrel, the vacuum system and the power cabinet. The lens barrel mainly has 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 mechanical vacuum pump, diffusion pump and vacuum valve, and through the pumping pipe connected with the lens barrel; power supply cabinet consists of a high-voltage generator, excitation current regulator and a variety of regulatory control unit.
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, by a very stable DC excitation current through the coil with a pole shoe generated by the strong magnetic field to focus the electrons.
The electron gun is a component consisting of a tungsten hot cathode, a gate and a cathode. It emits and forms an electron beam with uniform velocity, so the stability of the accelerating voltage is required to be not less than one part in ten thousand.
Electron microscopes can be divided into transmission electron microscopes, scanning electron microscopes, reflection electron microscopes and emission electron microscopes according to their structure and use. Transmission electron microscope is often used to observe those with ordinary microscopes can not distinguish the fine structure of the material; scanning electron microscope is mainly used to observe the morphology of solid surfaces, but also with the X-ray diffractometer or electron spectrometer combined to constitute the electron micro-is formed by the sample of the atoms to the scattering of the electron beam. Thinner or less dense parts of the sample have less scattering of the electron beam, so that more electrons pass through the objective lens light bar and participate in the imaging, appearing brighter in the image. Conversely, thicker or denser parts of the sample appear darker in the image. If the sample is too thick or dense, the contrast of the image deteriorates and can even be damaged or destroyed by absorbing energy from the electron beam.
Uses of Electron Microscopes
Electron microscopes can be divided into transmission electron microscopes, scanning electron microscopes, reflection electron microscopes and emission electron microscopes according to their structure and use. Transmission electron microscope is often used to observe those with ordinary microscopes can not distinguish the fine structure of the material; scanning electron microscope is mainly used to observe the morphology of the solid surface, but also with the X-ray diffractometer or electron spectrometer combined to form the electron microprobe, used for the analysis of the material composition; emission electron microscope for the study of the surface of the self-emission of electrons.
