What is the working principle of Scanning electron microscope?
Due to the fact that transmission electron microscopy is used for TE imaging, it is necessary to ensure that the thickness of the sample is within the size range that the electron beam can penetrate. To achieve this, various cumbersome sample preparation methods are needed to transform large-sized samples to a level acceptable for transmission electron microscopy.
The goal pursued by scientists is to directly utilize the material properties of sample surface materials for microscopic imaging.
Through efforts, this idea has become a reality - Scanning electron microscope (SEM).
SEM - Electron optics instrument that scans the surface of the observed sample with a very thin electron beam, collects a series of electronic information generated by the interaction between the electron beam and the sample, and images after conversion and amplification. It is a beneficial tool for studying three-dimensional surface structures.
Its working principle is:
In the high vacuum lens tube, the electron beam generated by the electron gun is focused into a fine beam by the electron convergence lens, and then scans and bombards the sample surface point by point to generate a series of electronic information (Secondary electrons, back reflection electrons, transmission electrons, absorption electrons, etc.). The detector receives various electronic signals, amplifies them by the electronic amplifier, and then inputs them into the picture tube controlled by the picture tube grid.
When scanning the surface of the sample with a focused electron beam, due to the different physical and chemical properties, surface potential, elemental composition, and concave convex morphology of the surface at different parts of the sample, the electronic information excited by the electron beam is different, resulting in the constant change of the electron beam intensity of the imaging tube. Finally, an image corresponding to the surface structure of the sample can be obtained on the fluorescent screen of the imaging tube. According to the different electronic signals received by the detector, the backscattered electron image, Secondary electrons image and absorption electron image of the sample can be obtained respectively.
As described above, a Scanning electron microscope mostly has the following modules: Electron optics system module, high-voltage module, vacuum system module, micro signal detection module, control module, micro displacement table control module, etc.
