Why does an electron microscope require a vacuum system?
Due to the slow movement of electrons in air, it is necessary to maintain the vacuum degree of the electron microscope through a vacuum system. Otherwise, molecules in the air will obstruct the emission of the electron beam and prevent imaging. Connect two types of vacuum pumps in series to obtain vacuum in the electron microscope tube. When the electron microscope is started, the first stage rotary pump obtains low vacuum as a pre vacuum for the second stage pump; The second stage uses an oil diffusion pump to achieve high vacuum.
Scanning electron microscopy uses high-energy electron beams to scan and image objects. To ensure imaging resolution, the electron beam needs to be collimated and focused like a beam. If it weren't for the vacuum or insufficient vacuum degree, high-energy electron beams would be absorbed or scattered when they hit air molecules, disrupting their collimation and making it impossible to image.
Vacuum has two functions: one is to prevent air molecules from scattering electrons, which can lead to poor focusing of the electron beam; Another is to avoid the loss of electron energy after collision with air molecules.
The importance of vacuum for electron microscopy: Vacuum plays a very important role in electron microscopy. When the electron microscope is working, the entire electron beam path and the sample to be analyzed will be placed in a high vacuum environment. If the vacuum degree is not high enough, inter electrode discharge may occur between the gate and anode of the electron gun, which may burn out the filament. Collisions between the electron beam and residual air particles can also cause scattering, which can prevent electrons in the electron beam from reaching the sample or distort the analysis.
The vacuum requirements of electron microscopes: In order to allow the electrons in the electron beam to move as smoothly as possible, the vacuum degree of electron microscopes usually needs to reach a high vacuum of the order of 1E-7mbar, or even an ultra-high vacuum of the order of 1E-10mbar; In addition to the vacuum degree, the vibration level during the operation of the vacuum pump is also crucial. Due to the small cross-section of the electron beam, the positioning accuracy on the sample is very high, and this accuracy can only be maintained in an environment with extremely low vibration levels; In addition, to avoid oil vapor contamination of the sample or internal components of the microscope, it is best to use an oil-free dry vacuum pump.
