Difference between electron microscope metallurgical microscope
The world's first electron microscope was built in Berlin in 1931 by M. Knoil and E. Rusk by adapting a detachable high-speed shadow tube oscilloscope with three lenses, a transmission electron microscope using a cold cathode electron source, and in 1934 M. Knoil and E. Rusk increased the resolution to 500 Å. The scanning electron microscope (SEM), abbreviated SEM, is a complex system that condenses electron-optical techniques, vacuum techniques, and fine mechanical structures.
Scanning Electron Microscope (Scanning ElectronMicroscope ), abbreviated as SEM, is a complex system; condensed electron-optical technology vacuum technology, fine mechanical structure and modern computer control technology. SEM is an accelerated high-voltage effect of the electron gun emitted by the electron through a multi-stage electromagnetic lens convergence into a small beam of electrons. Scanning in the specimen surface, excitation of a variety of information, through the reception of this information, amplification and display imaging, in order to analyse the specimen surface. The interaction of the incident electrons with the specimen produces the types of information shown in Figure 1. The two-dimensional intensity distribution of this information varies with the characteristics of the specimen surface (these characteristics are surface morphology, composition, crystal orientation, electromagnetic properties, etc.), is a variety of detectors to collect the information in order, the ratio of the information converted into a video signal, and then transmitted to the simultaneous scanning of the picture tube and modulation of its brightness, you can get a response to the surface of the specimen scanning map. If the signal received by the detector is digitised and converted into a digital signal, it can be further processed and stored by a computer. Scanning electron microscopes are mainly designed for the observation of thick block specimens with large height differences and rough unevenness, and are therefore designed to highlight the depth-of-field effect, and are generally used to analyse fractures as well as natural surfaces that have not been artificially treated.
Electron microscope and metallurgical microscope
First, the light source is different: metallurgical microscope using visible light as a light source, scanning electron microscope using electron beam as a light source imaging.
Second, the principle is different: metallurgical microscope using geometric optics imaging principle for imaging, scanning electron microscope using high-energy electron beam bombardment of the sample surface, excitation of a variety of physical signals on the surface of the sample, and then the use of different signal detectors to accept the physical signals converted into image information.
Third, the resolution is different: metallurgical microscope because of the interference and diffraction of light, the resolution can only be limited to 0.2-0.5um between. Scanning electron microscope because the use of electron beam as a light source, the resolution can reach between 1-3nm, so the tissue observation of metallurgical microscope belongs to the micron level analysis, scanning electron microscope tissue observation belongs to the nanometer level analysis.
Fourth, the depth of field is different: general metallurgical microscope depth of field between 2-3um, so the surface smoothness of the sample has a very high degree of requirements, so its sampling process is relatively complex. While the scanning electron microscope has a large depth of field, large field of view, imaging rich in three-dimensional sense, can directly observe a variety of specimens uneven surface microstructure.
