Scanning Electron Microscope

The electron microscope is an expensive, bulky and complex instrument. It uses electrons instead of visible light as the illumination source, and uses electromagnetic lenses instead of glass lenses to deflect electrons. It must have strong and stable voltage and current as well as extremely high The degree of vacuum is required for normal operation, and the handling of samples is even more stringent. In addition, precise calibration, proper maintenance and dedicated operation are also necessary conditions for the use of electron microscopes. When electrons are irradiated on the sample, if the sample is thin enough, the electrons may pass directly through the sample without encountering any obstacles, which is called transmitted electrons; if they impact the nuclei of the constituent atoms on the sample, due to the interaction between the electrons and the nuclei The mass difference between the two is very large. The electrons will be deflected or rebounded at a considerable angle. The rebounded electrons are called backscattered electrons. If they hit the electrons surrounding the component atoms in the sample, they will not be ejected except themselves. In addition to deflection, other electrons may also be knocked out of their original electron orbits. Such electrons that are separated from the atom due to impact are called secondary electrons. According to the above-mentioned method of irradiating electrons on the sample and the type of information received and displayed, electron microscopes can be divided into transmission electron microscopes (Transmission Electron Microscope, TEM) and scanning electron microscopes (Scanning Electron Microscope, SEM). Transmission electron microscopes use penetrating electrons to create images; scanning electron microscopes use secondary electrons or backscattered electrons to create images.

A transmission electron microscope is mainly composed of a main body, a vacuum system and an electronic system. The main body also includes a column and some control buttons. The column is the main part of the electron microscope. The most important parts, from top to bottom, are the illuminating system, image forming system and image translating system. The vacuum system includes a vacuum pump and a cooling system. As for the circuit system, in addition to providing the powerful accelerating voltage and current of the electron microscope to accelerate and deflect electrons, it also controls the operation and calibration of the microscope.