Scanning Electron Microscope, abbreviated as SEM, is a complex system; Concentrated electronic optical technology, vacuum technology, fine mechanical structure, and modern computer control technology. Scanning electron microscopy is the process of combining electrons emitted by an electron gun under accelerated high pressure into a small electron beam through a multi-stage electromagnetic lens. Scan the surface of the sample to excite various information, and analyze the surface of the sample by receiving, amplifying, and displaying imaging of this information. The interaction between the incident electron and the sample produces the type of information shown in Figure 1. The two-dimensional intensity distribution of this information varies with the characteristics of the sample surface (such as surface morphology, composition, crystal orientation, electromagnetic properties, etc.). It is the process of sequentially and proportionally converting the information collected by various detectors into video signals, and then transmitting them to synchronously scanned picture tubes and modulating their brightness to obtain a scanning image that reflects the surface condition of the sample. If the signal received by the detector is digitized and converted into a digital signal, it can be further processed and stored by the computer. Scanning electron microscopy is mainly used to observe thick block specimens with large height differences and roughness, thus highlighting the depth of field effect in design. It is generally used to analyze fractures and natural surfaces that have not been artificially treated.
1, Different light sources: A metallographic microscope uses visible light as the light source, while a scanning electron microscope uses an electron beam as the light source for imaging.
2, The principle is different: a metallographic microscope uses geometric optical imaging principles for imaging, while a scanning electron microscope uses high-energy electron beams to bombard the surface of the sample, stimulating various physical signals on the surface. Then, different signal detectors are used to receive physical signals and convert them into image information.
3, Different resolutions: Due to the interference and diffraction of light, the resolution of a metallographic microscope can only be limited to 0.2-0.5um. Due to the use of an electron beam as the light source, scanning electron microscopy can achieve a resolution between 1-3nm. Therefore, the microstructure observation of metallographic microscopy belongs to microscale analysis, while the microstructure observation of scanning electron microscopy belongs to nanoscale analysis.
4, Different depth of field: Generally, the depth of field of a metallographic microscope is between 2-3um, so it has extremely high requirements for the surface smoothness of the sample, so its sample preparation process is relatively complex. Scanning electron microscopy, on the other hand, has a large depth of field, a wide field of view, and a three-dimensional imaging effect. It can directly observe the fine structures of various uneven surfaces of samples.
