The difference between electron microscopy and metallographic microscopy
Scanning electron microscope principles
Scanning ElectronMicroscope, abbreviated as SEM, is a complex system that condenses electron optical technology, vacuum technology, fine mechanical structure and modern computer control technology. The scanning electron microscope collects the electrons emitted by the electron gun into a small electron beam through a multi-stage electromagnetic lens under the action of accelerating high voltage. Scanning on the sample surface stimulates various information, and by receiving, amplifying and displaying the information, the sample surface can be analyzed. The interaction between incident electrons and the sample produces the types of information shown in Figure 1. The two-dimensional intensity distribution of this information changes with the characteristics of the sample surface (these characteristics include surface morphology, composition, crystal orientation, electromagnetic properties, etc.), which is a sequential and proportional conversion of the information collected by various detectors. The video signal is converted into a video signal and then sent to a synchronously scanning picture tube and its brightness is modulated to obtain a scanned image reflecting the surface condition of the sample. If the signal received by the detector is digitally processed 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 specimens with large height differences and rough unevenness. Therefore, the design highlights the depth of field effect. It is generally used to analyze fractures and natural surfaces that have not been artificially processed.
Electron Microscope and Metallurgical Microscope
1. Different light sources: Metallographic microscopes use visible light as the light source, and scanning electron microscopes use electron beams as the light source for imaging.
2. Different principles: Metallographic microscopes use geometric optical imaging principles to perform imaging, while scanning electron microscopes use high-energy electron beams to bombard the sample surface to stimulate various physical signals on the sample surface, and then use different signal detectors to receive the physical signals and convert them into images. 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. Because the scanning electron microscope uses electron beams as the light source, its resolution can reach between 1-3nm. Therefore, the tissue observation under the metallographic microscope belongs to micron-level analysis, while the tissue observation under the scanning electron microscope belongs to nano-level 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 complicated. The scanning electron microscope has a large depth of field, a large field of view, and a three-dimensional image, and can directly observe the fine structures of the uneven surfaces of various samples.
