Scanning electron microscope is an instrument that uses electron beams and electronic lenses instead of light beams and optical lenses based on the principle of electron optics, so that the fine structure of the substance is imaged at a very high magnification.

In recent years, the research on scanning electron microscope and scanning electron microscope manufacturing has made great progress: on the one hand, the resolution of the electron microscope has been continuously improved, the point resolution of the transmission electron microscope has reached 0.2-0.3nm, and the lattice resolution has reached 0.1nm From left to right, through electron microscopy, people have been able to directly observe atomic images; on the other hand, in addition to transmission electron microscopy, many kinds of electron microscopy have been developed, such as scanning electron microscopy, analytical electron microscopy, and so on. Although the resolving power of the electron microscope is far better than that of the optical microscope, the electron microscope needs to work under vacuum conditions, so it is difficult to observe living organisms, and the irradiation of electron beams will also damage biological samples.

Three major components and characteristics of electron microscope

The electron microscope consists of three parts: an electron optical system, a vacuum system and a power supply system. The following editor will briefly introduce the three parts:

1. Electron optical system

1. The electronic optical system mainly consists of electronic gun, electronic lens, sample holder, phosphor screen and camera mechanism, etc. These components are usually assembled from top to bottom into a cylinder.

2. The electron gun is a component composed of a tungsten wire hot cathode, a grid and a cathode. It can emit and form an electron beam with uniform speed, so the stability of the accelerating voltage is not less than one ten thousandth.

The electron lens is the most important part of the electron microscope lens barrel. It uses a spatial electric or magnetic field symmetrical to the axis of the lens barrel to bend the electron track to the axis to form a focus. Its function is similar to that of a glass convex lens to focus the beam, so it is called electron lens. Most modern electron microscopes use electromagnetic lenses, and the electrons are focused by a strong magnetic field generated by a very stable DC excitation current through a coil with pole shoes.

2. Vacuum system

In order to ensure that the entire channel only interacts with the sample and does not collide with air molecules, therefore, the entire electronic channel from the electron gun to the camera chassis must be placed in a vacuum system, the general vacuum degree is 10-4 ~10-7 mmHg.

3. Power supply system

Transmission electron microscope needs two parts of power supply: one is to supply the high voltage part of the electron gun, and the other is to supply the low voltage steady current part of the electromagnetic lens. The stability of the power supply is an extremely important indicator of the performance of the electron microscope. Therefore, the main requirement for the power supply system is to generate a high and stable acceleration voltage and the excitation current of each lens. In addition to the above-mentioned power supply, modern instruments also have automatic operation program control systems and data processing computer systems.