Several differences between scanning electron microscopes and metallographic microscopes
In material analysis experiments, we often use scanning electron microscopes and metallographic microscopes. What are the differences in the use of these two devices? Tianzong Testing (SKYALBS) has summarized some information here for reference and shares it with everyone.
A metallurgical microscope is a microscope that uses incident illumination to observe the surface (metallic structure) of a metal sample. It is developed by perfectly combining optical microscope technology, photoelectric conversion technology, and computer image processing technology. A high-tech product that can easily observe metallographic images on a computer, thereby analyzing, rating, and outputting and printing images.
Scanning electron microscopy (SEM) is a microscopic morphology observation method between transmission electron microscopy and optical microscopy. It can directly use the material properties of sample surface materials for microscopic imaging. Secondary electron signal imaging is mainly used to observe the surface morphology of the sample, that is, an extremely narrow electron beam is used to scan the sample, and various effects are produced through the interaction between the electron beam and the sample, the main one being the secondary electron emission of the sample. Secondary electrons can produce an enlarged topographic image of the sample surface. This image is established in time sequence when the sample is scanned, that is, the enlarged image is obtained using point-by-point imaging.
The main differences between the two microscopes are as follows:
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.
In general, optical microscopes are mainly used for observation and measurement of micron-level structures on smooth surfaces. Because visible light is used as the light source, not only the surface tissue of the sample can be observed, but also the tissue within a certain range below the surface can also be observed, and Optical microscopes are very sensitive and accurate for color recognition. Electron microscopes are mainly used to observe the surface morphology of nanoscale samples. Because SEM relies on the intensity of physical signals to distinguish tissue information, the images of SEM are all black and white, and SEM is powerless to identify color images. However, the scanning electron microscope can not only observe the organizational morphology of the sample surface, but can also be used for qualitative and quantitative analysis of elements by using accessory equipment such as energy spectrum analyzers, and can be used to analyze information such as the chemical composition of sample micro-regions.
