Why is the resolution of an electron microscope so much higher than that of an optical microscope?
Because electron microscopes use electron beams and optical microscopes use visible light, and the wavelengths of electron beams are shorter than those of visible light, electron microscopes have much higher resolution than optical microscopes.
The resolution of a microscope is related to the cone angle and wavelength of the electron beam passing through the sample.
The wavelength of visible light is about 300 to 700 nanometers, while the wavelength of the electron beam is related to the accelerating voltage. According to the principle of wave-particle duality, the wavelength of high-speed electrons is shorter than that of visible light, and the resolution of the microscope is limited by the wavelength it uses, so the resolution of electron microscopes (0.2 nanometers) is much higher than that of optical microscopes. (200 nm).
The application of electron microscope technology is based on the basis of optical microscope. The resolution of optical microscope is 0.2μm, and the resolution of transmission electron microscope is 0.2nm. times.
Although the resolution of an electron microscope is much higher than that of an optical microscope, it has some disadvantages:
1. In an electron microscope, the sample must be observed in a vacuum, so live samples cannot be observed. With the advancement of technology, environmental scanning electron microscopes will gradually realize the direct observation of living samples;
2. When processing the sample, it may produce structures that the sample does not have, which aggravates the difficulty of analyzing the image afterward;
3. Due to the strong electron scattering ability, it is prone to secondary diffraction, etc.;
4. Because it is a two-dimensional plane projection image of a three-dimensional object, sometimes the image is not unique;
5. Since transmission electron microscopy can only observe very thin samples, it is possible that the structure of the surface of the material is different from the structure of the interior of the material;
6. For ultra-thin samples (below 100 nanometers), the sample preparation process is complicated and difficult, and the sample preparation is damaged;
7. The electron beam may destroy the sample by collision and heating;
8. The price of electron microscope purchase and maintenance is relatively high.
